That is the Question.

By Roger V. Morrison, PF, RRC, Deer Ridge Consulting, Inc.

The spray polyurethane foam (SPF) community has been installing unvented-conditioned attic in homes for decades.  But with the changes in the International Residential Code, which were first implemented in the 2004 Supplement, the code now recognized the practice, and unvented-conditioned attics are broadly accepted.  The SPF community has embraced this development because SPF’s combination of high R-value and low air permeability make it an ideal insulation for this application.

But, do unvented attics always make sense?  In my opinion, the answer is an unequivocal “No”.

Advocates of unvented attics claim they save energy over vented attics, but these savings occur only under certain circumstances.  There are good reasons to install unvented attics, but there are also good reasons to insulate the attic floor and vent.

When considering whether or not to vent an attic, my default position is to vent.  That is, install SPF insulation on the attic floor and provide the classic soffit, ridge, and/or gable ventilation that the building codes require.

The main reason behind my opinion lies in the geometry and thermodynamics of attics.  The relationship between heat loss and insulation means that increasing either the area or the temperature difference increases heat transfer proportionally. 

Consider, for example, a simple rectangular, one-story house, 35 feet (10.7 m) wide by 70 feet (21.3 m) long, with a 6:12 pitch shingle roof that has its axis parallel to the length of the house and the gable ends.

Should we insulate the attic floor or the roof line?

First, take a look at the comparative areas that must be insulated.  The footprint of the attic floor is 1,750 square feet (162.6 m2), but the footprint of the roof line and gable ends adds 513 square feet (47.7 m2), increasing the total insulated area to 2,263 square feet (210.2 m2).  The roof line and gable ends add 29 percent more area that needs to be insulated.  And since heat transfer is proportional to area, insulating the roof line and gable ends contributes 29 percent greater heat loss and/or gain.

Next, take a look at the comparative temperature differences.  Temperatures of shingles and attics depend on many factors, far too complex for the scope for this article.  But the net effect is that the temperature difference across the insulation of an unvented-conditioned attic will be much greater than the temperature difference across insulation on the attic floor with venting.

Why is this?

The temperature difference across insulation in a vented attic (insulation is placed on the attic floor) depends on the attic temperature and the interior temperature.  And when the attic is vented, its temperature is lowered by the air circulation in to and out of the attic.  So on typical sunny, summer day when shingle temperature is 165 F (73.9 C), attic temperature may be in the neighborhood of 120 F (48.9 C).  With an interior temperature of 75 F (23.9 C), the temperature difference would be 120 – 75 = 45 F (7.2 C).

In an unvented-conditioned roof, with insulation applied to the underside of the roof deck, the exterior side of the insulation will be close to the temperature of the shingles (and shingles over an insulated deck will be slightly higher than those over a vented deck).  The underside (interior) temperature of the insulation will be close to the interior temperature.  So on a hot, sunny day, the shingle temperature may be 170 F (76.7 C) while the interior temperature is around 75 F (23.9 C).  Allowing for the insulating effects of air films, roof decking, ceiling, etc., the net temperature difference across the insulation would be approximately 165 – 80 = 85 F (29.4 C).

The temperature difference across the insulation in the unvented attic is almost twice as much as the vented attic, and this temperature difference means more heat transfer. 

If we assume, in both cases, that the insulation has an R-value of 30, the heat gains for each case are:

A= A x Δ T         Qvented = 1750 x 45 = 2630 Btu/hr      Qunvented= 2263 x 85 = 6410 Btu/hr              

          R                                         30                                                                           30

As can be seen, the combined effects of greater area and greater temperature difference in the unvented-conditioned attic result in a heat gain of 3,780 Btu/hr more than the vented attic.  This is equivalent to almost 1/3 of a ton (302.4 kg of air equal to 12,000 Btu/hr).  Obviously, this example represents extreme conditions, not those a house would really experience with daily and annual temperature fluctuations, but it still demonstrates the point.

Based on this analysis, the obvious answer to “should we insulate the attic floor or the roof line?” would be:  “Insulate the attic floor.”

 But not so fast.  There are important factors I haven’t mentioned.

In spite of the greater heat transfer (and energy consumption) that unvented-conditioned attics will experience, there are some excellent reasons to install them.

• Ductwork: Probably the most widely mentioned reason for unvented-conditioned attics is the energy savings that result from HVAC duct losses.  Then ducts are run through an attic, the energy losses from phusical and thermal leaks can be considerable.  In fact, by moving the duct work within the thermal envelope (as in an unvented-conditioned attic), the net energy savings can be dramatic.
• Recessed Lights:  With an unvented-conditioned attic, recessed or can lights can be installed without the expensive need to separately air seal and insulate them.
• Additional Floor Space: Often unvented attic space can be converted to occupied space with little additional cost.  Space can be added to a home this way either during initial construction or as later remodeling project.  Either way, this “harvesting of space” can add considerable value to the house.
• Wind and Water Mitigation: Hurricane-prone areas and other regions subject to high winds and wind-driven rain benefit from having SPF applied to the roof line.  Wind uplift resistance is enhanced and the likelihood of rain penetrating vents is reduced.
• Wild land-Urban Interface Zones: Wind can drive embers and burning brands into attic vents, starting fires and causing catastrophic damage.  Unvented-conditioned attics eliminate the vents, reducing this fire hazard.
• Ice Damming: One of the most common causes of ice dams is having a non-uniform temperature profile of the roof surface can eliminate these temperature differences and the subsequent ice buildup and damming.
• Architectural Options: The attics of some house designs are impractical (or impossible) to vent.  By designing unvented-conditioned attics, architects can be much more creative with roof lines and configurations.
• Construction Scheduling:  The insulation  package can be installed in a single visit; vented attics require that the insulation contractor return after the dry wall has been installed
• Installation Access: Installing SPF insulation to the underside of roof decks before the drywall ceiling is installed simplifies access, speeds up the insulating installation, and avoids difficult-to-insulate tight spots.

So, should we insulate the attic floor or the roof line?

Simple answer: Insulate the roof line with one or more of the factors discussed above are applicable; otherwise, insulate the attic floor.  SPF can be applied in either configuration and will provide excellent long-term insulation and an air seal in one product.

It’s perhaps one of the greatest challenges of a homeowner’s life: getting and keeping your home organized. As those who have many years of home ownership under their belts know, it only gets tougher to keep your house, closets and drawers in working order as life gets busier and stuff gets acquired. The good news is that there are plenty of simple, affordable and effective ways to not only get organized but stay that way as well, no matter how overwhelming the task may seem right now.

A good place to start is by designing a closet to your needs and Toler Insulating on Airpark Drive in Lynchburg knows this process better than most. This locally-owned, eco-friendly business employs a closet specialist by the name of Anders Sunwall. Owner Wayne Toler has been in business for 15 years but, recently, he decided to provide customers with “after paint products.” This includes things like closet shelving and light fixtures; basically the finishing touches to any new home or remodeling project. Sunwall, a Lynchburg native, came on board in 2007 to focus on designing and remodeling closets.

Toler offers Rubbermaid shelving products, which carry the “Green Guard” stamp and provide the client with the choice of coated wire or melamine shelving systems. The latter comes in a variety of colors from stark white to cherry wood finish.

“We have worked very hard to provide our customers with these products for less than you can buy them at Lowes,” Sunwall said, and this effort to offer a discount includes the cost of planning and installation.

Sunwall can plan a fully interchangeable and flexible shelving system to fit your changing needs. He even provides a nifty 3D digital image of your design before he installs it.

So how does the process work? First, Sunwall comes to your home to identify your needs and assess your budget.

“We work to fit anybody’s price range,” he explained, adding that in today’s economy, he feels it is important to offer ideas for lower cost products without sacrificing quality. “I don’t want to sell something I don’t believe in… Right now, I can go home knowing I’ve not only offered a service by helping the customer get organized, but I’ve also saved them money doing it.”

If you are like many women, you might run into a shoe dilemma (as in, having far too many!) when it comes to your closet. For this problem, Sunwall suggests making use of the closet’s side wall. By installing Rubbermaid wire racks that hang them upside down and at a slant (where the back lip becomes the shoe holder), your closet suddenly begins to look much like a department store’s racks. This gives shoe lovers the option of stacking three pairs of shoes across each shelf and, therefore, quickly cleaning up closet floors.

Of course, hiring a consultant may not be a realistic option for everyone, in which case, you should consider clearing out any excess first before organizing yourself. Just don’t take it all to the dump! There are plenty of ways your cast-offs can help out our community, like the numerous Goodwill stores in the area. With the very important mission of “Helping people and families in our community achieve a better life through work and independence,” last year alone, the local branch of Goodwill served 18,225 individuals in our community, with 92 cents out of every dollar of revenue going directly to support training and employment programs for individuals with disabilities and disadvantages.

Suni Heflin, Goodwill of the Valleys Market Manager, says there is a myth circulating that Goodwill stores are simply places for the economically challenged.

“We help people who need a hand-up, not a hand-out,” she said.

Many people don’t realize that the stores not only train disabled and disadvantaged workers, but they also help bring area youth and senior citizens into the workforce. Last year alone, they assisted more than 1,000 local people who lost their jobs due to company closings and layoffs through job training and placement.

Heflin says all of the local stores accept donations every day of the week, and all of the centers’ hours are listed at http://www.goodwillvalleys.com/. The stores don’t just accept clothing, but also shoes and accessories, house wares and small appliances, electronics, furniture, toys and games. They will not accept large appliances, mattresses or anything that has a motor and runs on gasoline because they are unable to dispose of these things responsibly. But, you need not only donate your nicer items.

A surprising fact: Goodwill Industries of the Valleys is also eco-friendly, having kept over 11 million pounds of materials out of area landfills through their retail and salvage operations. Although they resell the gently used items in their retail stores, they also take torn and broken items for their salvage and recycling operations. This includes all old computers and electronic parts. Heflin says they participate in the Reconnect Program with Dell which works to recycle any brand of computer in any condition in order to reuse the parts. Both Goodwill and Dell are committed to recycling these parts and keeping them out of our landfills.

The YWCA of Central Virginia is also happy to accept donations.

“Anything ladies or girls like would be gratefully received by the residents of the YWCA,” JoAnne Nickerson said, adding that this only includes very gently used items, if used at all. “Our motto is empowering women. These women are not homeless or destitute. They pay monthly rent and work to earn a living.”

In addition to clothes, the YWCA also accepts furniture, house wares, and hygiene items.

If you find yourself having a hard time getting rid of sentimental items, earning some extra cash might help you to let go. In this case, consider one of the many local consignment stores in town. For instance, “Nice as New” on Linkhorne Drive accepts donations by appointment only and all items must be gently used, freshly laundered and on hangers. Nice as New accepts up to 35 items at one time but does not accept items with stains, tears or wrinkles. Items will be held in the store for two months. If they sell, you get 40 percent. The only catch is remembering to pick the items up by the specified date. Otherwise, they will be donated to local charities. The same is true of many other local shops of this nature like “On Second Thought” on 221 and “New to You” on Old Forest Road.

After you’ve cleaned out your closet’s overstock, it’s time to get creative. Star Hansen of HGTV suggests sorting remaining items into categories of long-term and short-term storage and immediate use. Those items for long-term storage, like the skinny jeans you just can’t bear to get rid of can be placed into vacuum sealed bags. These affordable bags slim down into easily stackable small packages, once the air is vacuumed out of them. They can then be stacked on the high, harder-to-reach shelves or in the basement or attic. Short-term storage like sweaters and boots for next fall can be placed into plastic storage bins stacked on the floor or shelves. Bins with rollers are also very useful since they slide easily under the bed.

Sunwall says one of the common problems with closets is the failure to use the vertical space, so he suggests installing a simple double hanging rod, which provides double the amount of space for clothing. While you are at it, replace all wire hangers with plastic ones to keep from damaging the shape of your clothing. Hansen also suggests making use of the affordable variety of hanging shoe racks, belt and tie hangers, and adjustable purse hangers for the backs of doors or the closet side walls.

Once you have that closet cleaned and your house de-cluttered, you might consider additional ways to keep your home neat and organized for the rest of the year. For this, Sharon or Michael Sprague at Merry Maids may be just the ticket. With 11 years of experience in the Lynchburg area and a great reputation, they specialize in helping people who are “overworked and out of time” by taking care of those pesky cleaning chores around the house. Although they don’t do closets, they will help keep the rest of the house neat and clean, and they offer “customized service to each home,” which includes working within your budget. For more information, check out http://www.merrymaids.com/.

No matter what stage of life you are in, there are many affordable ways to get organized. Remember that spring and summer are the best times of the year for many people for a thorough cleaning, making it the perfect time to donate your unwanted clutter and overstock from around the house. While you’re at it, don’t forget to take advantage of the many local businesses who will work hard to help you stay organized this year.

Five Easy Steps for Cleaning Out the Junk Drawer

1. The first step to take when tackling the dreaded junk drawer is to immediately dump out all of its contents. This will not only give you a better idea of what has been lurking in there, but it will help you form two piles�”what to keep” and “what to toss.”
2. Exploring the contents of your junk drawer will no doubt reveal some interesting finds. Resist the temptation to keep anything that is not important, useful or that you did not know was missing in the first place. Throw away everything in your “toss” pile.
3. Divvy up the contents of your “keep” pile. Everything has a place but the “Catch All” drawer is just where they tend to collect. The best strategy is to divide the items by the rooms they belong in. When you are finished, immediately take those items to their proper places.
4. Realistically, you are still going to have lost items that don’t seem to have a place elsewhere. These items, and these items only, are then left to reside in the “Catch All” drawer.
5. Purchase a desk divider, silverware holder or anything else with separate compartments and then take the remaining items and neatly organize them. Be sure to label anything that is not immediately recognizable (like parts to a piece of equipment). Finally, try your best to keep this drawer as clean as possible by constantly placing items that do not belong in the “Catch All” drawer in their respective spots.

One of the largest growing uses of spray polyurethane foam (SPF) insulation is in residential attics and crawl spaces.  As with all other foam insulation applications, this use is regulated by building codes to assure that occupants are properly protected from the risk of fire.  In order to demonstrate compliance with these requirements, the spray foam supplier typically performs fire tests, the results of which are submitted to an evaluation organization, such as the International Code Councils Evaluation Services (ICC-ES), for review.  A product’s performance is assessed against an Acceptance Criteria meant to clarify code requirements or to provide a technical basis for products or systems that are alternates to what is specified in the code.  Through a public hearing process, the ICC-ES developed the Acceptance Criteria for Spray-applied Foam Insulation (AC 377).

Recent modifications to the fire testing portion of AC377 were approved by the ICC-ES Committee in June 2009.  The new protocol is based on code-compliant assemblies, and creates a credible standard for flammability performance for SPF installed in attic and crawl space applications.  (Note: Performance in flammability tests does not necessarily predict how a material will perform in an actual fire.

Code Requirements

According to the International Building Code (IBC 2603.4)  and the International Residential Code (IRC R316.4), all foam plastic insulation must be separated from the interior of the building by an approved 15 minute thermal barrier, such as ½ inch (1.27cm) gypsum wall board or equivalent material.  This thermal barrier may be omitted if certain conditions are met in attics and crawl spaces.  Specifically, entry must be restricted to service of utilities AND the foam plastic must be protected from ignition with a code specified material. 

Section 316.5.3 of the IRC prescriptively defines the following six materials as ignition barriers:

• 1 ½ – inch (3/81 cm) mineral fiber insulation
• ¼ – inch (0.64 cm) wood structural panels
• 3/8 – inch (0.95) particleboard
• ¼ – inch (0.64) hardboard
• 3/8 – inch (0.95) gypsum wall board
• 16 mil (0.41 mm) corrosion resistant steel

Note that these materials used as ignition barriers are not necessarily as protective as thermal barriers.  Unlike thermal barriers, these materials are not required to limit the average temperature rise on the unexposed surface to less than 250 F (121.11 C) after a 15 minute exposure to an ASTM E 119 temperature curve, not is there a requirement for these materials to stay in place for at least 15 minutes when subject to specific fire tests.

Special Approvals Allowed By Code

The use and implementation of the prescribed ignition barriers over SPF insulation in attics and crawl spaces have proven to be awkward and inefficient.  Fortunately, the building codes allow for special fire tests to prove equivalent performance of alternate assemblies.  In general, these fire tests must be related to the end-use configuration, and the finished foam plastic assembly must be tested in the maximum thickness and density intended for use.

Options exist in the building codes to perform testing on the assembly to qualify SPF without a thermal barrier.  Passing these tests, with more stringent requirements that tests for ignition barrier equivalence, would allow the assembly to be used in lieu of the thermal barrier.  Specific testing includes NFPA 286 (with criteria from IRC R302.9.4), UL 1040, UL 1715 or FM 4880.  Assemblies passing these tests can also be used as an alternate to using code-prescribed ignition barriers. 

The building codes also allow code-prescriptive ignition barriers to be substituted with an assembly that can show at least equivalent performance.  Again, these fire tests must be related to end-use configuration.  Typically, the baseline is set based on performance of a prescribed ignitions barrier over the SPF in question.

The Route to Special Approvals of Alternate Assemblies

Although the ICC-ES officially came into being on February 1, 2003, it has a history of over 70 years.  The previously existing four building product evaluation services in the US combined their operations into one, the ICC-ES.  The ICC-ES evaluates building products for compliance with the code and issues reports on these products free of charge to code officials, contractors, and any others with an interest in the building industry.  These reposts are only advisory since it is only the code official or other authority having jurisdiction that can grant final approval for product use.

The foam plastic industry has worked with the ICC-ES to develop specific Acceptance Criteria (AC) for its products.  These ACs are important because they can address products that fall under code provisions that are not sufficiently clear, such as fire testing and approval of alternate assemblies in attics and crawl spaces.  These foam plastic specific ACs are:  AC12 for Foam Plastic Insulation and AC377 for Spray-Applied Foam Plastic Insulation.

Note that these ACs are intended solely for the use in development of the ICC-ES evaluation reports.  The ICC-ES has not approved AC usage by other evaluation entities in publishing code-compliance reports or for product certification activities.

Complications of Comparative Testing

By definition, comparing performance of a test assembly to a baseline assembly requies two fire tests.  Selection of an appropriate code complying baseline is important to the credibility of the test.  This was the case in the original AC377, where a comparative crawl space test, SwRI 99-02, developed at Southwest Research Institute, was used to eliminate the ignition barrier over foam plastic insulation altogether.  In April 2000, the International Conference of Building Officials Evaluation Service (ICBO ES) allowed for testing to qualify an alternate ignition barrier material or system utilizing the comparative crawl space test, SwRI 99 – 02, with Kraft paper faced fiberglass batts as an ad hoc baseline assembly [1].

As long as the foam plastic outperformed the fiberglass, the construction was approved for use in attics and crawl spaces.  This policy was later adopted by ICC-ES.  Although the ICBO mentioned three acceptable protocols for testing, the Kraft-faced fiberglass was chosen as the baseline by many companies.  Passing performance in this test allowed for omission of the prescribed ignition barrier.  One problem with the ICBO-ES, and later ICC_ES policy, was that the orientation of the Kraft paper was not specified.  Leaving the Kraft paper exposed is a non-compliant construction (IRC R302.10.1 and Exception 1, IBC 719.2.1 and 719.3), and it is not a prescriptive ignition barrier.

Another complication factor was that passing the comparative crawl space test also allowed elimination of the ignition barrier in the attic space, despite the differences in crawl space size and geometry compared to an attic space.

An Interim Solution

The ICC-ES took action in late 2007 by asking SPFA to propose a new approach for fire performance testing of attics and crawl spaces.  SPFA formed an Attics and Crawl Space Task Force in early 2008 to address this request.  Based on a recommendation from SPFA, ICC-ES adopted a fixed time to flame threshold for performance in SwRI 99-02 in May 2008 thereby eliminating the need for two comparative tests and providing a consistent baseline [2].  This recommendation became known as AC377 Appendix B and was seen by ICC-ES as an interim solution.  It allowed SPFA time to develop a more rigorous proposal to meet the intent of the code.  All new and renewed  evaluation reports issued after May 2008 and before June 2009 were subject to the interim requirements.  Appendix B as a fire test option expired in June 2009.

The SPFA Task force Protocol

The SPFA, with funding from member companies and the Center for the Polyurethanes Industry, initiated a study to find a code compliant solution for testing spray foam for attic and crawl space applications.  Other foam plastic insulation industries were consulted during protocol development.  Recognizing that the spray foam industry would use the same test baseline, the SPFA embarked on development of a large scale fire test protocol based on a widely-accepted room corner test, a modified NFPA 286.

NFPA 286 is a room corner fire test, utilizing an eight-foot (2.44m) high, eight-foot (2.44m) wide by 12 foot (3.66m) long room with a controlled sand gas burner ignition source in the corner.  A code approved prescriptive ignition barrier was investigated as the comparative baseline:  SPF covered with ¼-inch (0.64cm) plywood.  Based on an average time for room flash-over from six of these tests, a Pass/Fail time threshold was assigned.

Tests were also preformed on SPF without the plywood to uncover any testing issues specific to SPF.  Because of the uneven surface of SPF, and based on heat-flux mapping of various ignition sources and their distance to the wall, the task force added a requirement for the SPF in the corner able the flame to be within a certain distance from the burner assembly.

Another requirement in the protocol is that the product or assembly being tested for approval must be uniform on both the walls and the ceilings.  For example, there is no option to apply an intumescent coating to the wall, but not the ceiling of the attic.  If a coating is used, it much be uniformly applied to both surfaces.

Attics can be made with carious slopes in the ceiling.  Instead of testing each possible slope for approval, this room corner test is conservative in that it evaluates the extremes of vertical wall and horizontal ceiling, eliminating the need to test each possible slope.

Currently, some manufacturers have ICC_ES reports that allow approval to cover only the vertical (wall) surface and leave the ceiling foam exposed.  In the extreme case, this approval would inadvertently allow exposed foam on the ceiling of the attic to be installed on a slope all the way to the floor of the attic.  The figure on page 32 uses a schematic to explain this point further.  Because most attic ceilings are not eight feet (2.44m) from the floor at their lowest point, like the test configuration, testing only the ceiling in a room corner test does not adequately represent attic use.  The requirement in the protocol that any thermally resistive coating be applied uniformly to all surfaces (Vertical and horizontal) eliminates the need to limit the approval to a specific configuration.  ICC-ES is allowing generic comparative room corner tests until June 2010, but will apply the SPFA test protocol requirements to any new submitted test data.  In addition, testing horizontal ceiling will no longer gain approval for sloped under-roof decks.

Generic Comparative Room corner Test (A1.2.2): Additional Conditions and Eventual Deletion

ICC-ES decided to allow AC377 appendix A1.2.2 to remain in place until June 2010.  During this period, any new tests submitted using this generic comparative room corner test will have the following additional criteria applied (based on SPFA recommendations from their development work):

• Care shall be taken to provide as smooth a surface as possible especially in the wall areas adjacent to, as well as above, the flame source
• For testing on walls, the maximum deviations of distance between the flame source and the foam surface are as described in AC377 Appendix X, Figure 3
• If approval is sought for the underside of roof deck only, approval will be granted only for use on horizontal surfaces at heights equal to or greater than the ceiling height tested
• If coverings are used over the foam, they shall be applied at the same thickness or minimum coverage rate to all foam surfaces

Option Available For Meeting Code Attics

The following options are detailed in AC377 for approved SPF use in attics:

• Use a code-prescribed ignition barrier (A1.1)
• Perform a special approval test “in lieu of thermal barrier” (A1.2.1)
• Perform a modified-NFPA 286 room corner test (Appendix X)
• Perform generic comparative room corner tests with ¼ inch (0.64cm) plywood baseline (A1.2.2, expires June 1, 2010)

Crawl Spaces

The following options are detailed in AC 377 for approved SPF use in crawl space:

• Use a code-prescribed ignition barrier (A2.1)
• Perform a special approval test “in lieu of thermal barrier” (A2.2.1)
• Perform a modified-NFPA 286 room corner test (SPFA Protocol, Appendix X)
• Perform comparative crawl space tests with ¼-inch (0.64cm) plywood baseline (A2.2.2 and Appendix C)

The acceptance of the SPFA Protocol by ICC-ES into the Acceptance Criteria for Spray-applied Foam Insulation (AC377, Appendix X) provides a number of credible options to demonstrate compliance with the code.  Furthermore, the testing options apply to a variety of SPF products and systems, including exposed spray foam or spray foam covered by an alternate ignition barrier, such as an intumescent coating.  Using the SPFA Protocol (Appendix X) allows an SPF supplier to gain acceptance of both attic and crawl space use from on test.

REFERENCE

1.  Gerber, B. “Recognition of Use of Foam Plastic Insulation in Attics and Crawl Spaces,” Subject MISC1-R2-0300 (MB/RK)  (Previously MISC2-0799).  International Conference of Building Officials Evaluation Services.  11 April 2000.

2.  Beaton, M.  “Proposed Revision to the ICC-ES Acceptance Criteria for Spray-Applied Foam Plastic Insulation.”  Subject AC377-0508-R1.  ICC-ES Evaluation committee memo, May 19, 2008.

Why Should You Be Concerned with Air Barriers?

Air Barriers control the unintended movement of air into and out of building enclosures.  A properly functioning Air Barrier System provides a barrier against both air leaks and diffusion of air caused by wind, stack, and mechanical equipment pressure.

When Air Barrier Protection is neglected it can cause an increase use in energy costs up to 30-40% in heating and 10-15% in cooling costs.  Not only is Air Barrier Systems energy sufficient but can also provide protection from pollutants.  Which includes water vapor leaks, the key component in formation of mold and smell.

With this reduction in both energy costs and cosmetic maintenance, a properly installed Air Barrier System will over time pay for itself!

Appropriate applications for open-cell and closed-cell foam insulation

Thermal insulation for low-rise residential construction has historically been dominated by loosefill and pre-formed blanket cavity-fill materials, primarily fiberglass and cellulose. With a new generation of building insulation materials and systems on the market, a careful assessment of their physical properties needs to be made in the context of potential applications to assure that performance matches expectations and that unintended consequences, in this case moisture related building-envelope failure, are avoided. This guideline focuses on performance benefits and the potential performance limitations of open-cell and closed-cell spray polyurethane foam.

SPRAY POLYURETHANE FOAM INSULATION

Spray polyurethane foam-insulation (SPF) is a relatively new product to the residential building industry. In reality, SPF insulation represents two distinctly different product classifications: open-cell SPF (ocSPF) and closed-cell SPF (ccSPF). Both categories of SPF are chemically similar and are applied in a two-part liquid spray consisting of polymeric MDI (methylene diphenyl diisocyanate) on one side, and a cocktail of polyol resins, surfactants, fire-retardants, and catalysts on the other. Compositionally, the most significant difference is in the blowing agents. Closed-cell foam primarily uses non-ozone depleting hydroflurocarbons (HFC’s), while open-cell primarily uses water. The formulations result in differing expansion reactions with closed-cell expanding about 35 to 50 times its original volume compared to open-cell which expands triple that to 150 times is original volume. In applying the foams, closed-cell is typically limited to 2”-3” thick layers per pass, with greater thicknesses made up of multiple layers. Opencell foam may be applied to full thickness in a single pass, generally up to 10”. Both types of SPF are excellent at air-sealing, a once overlooked, but critical aspect of insulated assemblies. The liquid-to-expanding foam process tends to fill gaps, cracks and voids responsible for uncontrolled air leakage. It is this attribute that makes SPF insulation performance superior to other typical insulations such as fiberglass or cellulose which are far less able to block air flow.  Both ocSPF and ccSPF are combustible, and as such are formulated with fire-retardants and other additives to decrease flame spread and smoke generation as measured by ASTM Standard E 84, Test for Surface Burning Characteristics for Building Materials. Each foam type generally falls into the area of less then 25 flame-spread index, and less then 450 on the smoke-developed index, dependant on thickness, manufacturer, and formulation.  Because of its categorization as combustible, SPF used in building assemblies is typically required to be fire-protected by a “thermal barrier” or an “ignition barrier”. The most relevant definition for that thermal barrier for our purposes is contained within the International Residential Code (IRC), which for most applications is a 15-minute thermal-barrier (the equivalent of ½” gypsum board) as tested under ASTM E 119. For some applications not within habitable space, such as attics and crawlspaces, an ignition barrier may suffice. Although similar in chemical composition, the differences represented by their respective physical properties and performance attributes are so significant, that potential applications need to be gauged separately: the two products are not interchangeable in all applications.

Open-Cell SPF 

Once installed, open-cell SPF consists of a three-dimensional matrix of interconnected open cells, hence the name. Alternately called half-pound foam, the finished material weighs approximately 0.5 PCF, and is soft and easily compressed. The material remains somewhat flexible, but once compressed will not fully expand back to its original shape as the open-cell voids are reduced through compaction. The resistance to thermal heat flow is obtained through the interconnected cell matrix which acts to inhibit air movement and conductive heat flow.

Typical R-values for open-cell SPF is approximately 3.6 per inch.

Open-cell SPF is excellent at blocking air-flow and is considered air-impermeable at typical application thicknesses. Although it is defined as air-impermeable, open-cell SPF is not vapor impermeable. At a typical thickness of 5”, open-cell foam is rated from 5 to 10 Perms (dependant on specific product). By definition, a vapor retarder has a Perm rating of 1.0 or less.

Open-cell SPF will also absorb and hold liquid water. The water source can be from pressure driven vapor diffusion, moisture from air leakage through finished wall and ceiling coverings, or bulk water through leaks. The amount of water capable of being held varies by specific product, but it can be significant; up to one-third by volume.

Open-cell SPF has a lower installed cost than ccSPF as its expansion ratio is higher given the same volume of liquid base ingredients. Retail installed cost of ocSPF varies but is generally in the $0.35-$0.40 per board-foot range or roughly $0.12 per R-1 per square-foot. 

Closed-Cell SPF   

At 2-lbs per cubic foot closed-cell SPF, alternately called 2-lb foam, is approximately four times denser than open-cell foam. Once set, the material remains rigid and more difficult to compress by hand-applied pressure. In compression closed-cell is ten times stronger than open-cell and  seven times stronger in tension. Closed-cell SPF is in fact utilized as structural adhesive at many modular-housing factories to glue gypsum board to wall studs and ceiling joists. Studies at the University of Florida and elsewhere have documented the structural advantage of using ccSPF to glue roof decking to trusses in hurricane-prone areas. Similarly studies have found that the racking strength of frame walls is substantially increased when ccSPF is used in the frame cavities: an advantage for seismic and hurricane zone construction. The largest difference however, is in the cell structure: Closed-cell foam maintains over 90% of its cells as closed, with the insulative gases contained within them trapped. Air or other gases do not communicate from one cell to the next. This property results in the key differences between open and closed-cell SPF’s: the R-value for typical closed-cell foam is R-6 per inch; the material is rigid and far more difficult to compress; and at typically applied thickness ccSPF is defined as a vapor-retarder, essentially moisture-vapor impermeable. Closed-cell SPF is hydrophobic and will not absorb water. Dependant on formulation, ccSPF can be appropriate for extreme cold-temperature applications such as liquefied-gas storage vessels, and rigorous-service building envelope uses such as low-slope (flat) roofs. Closed-cell SPF has a higher installed cost than ocSPF mainly because there is more material per volume due to the lower expansion ratio. Retail installed cost of ccSPF varies but is generally in the $1.10-$1.25 per board-foot range or about $0.20 per R-1 per square-foot (about 60 percent higher than open-cell for R-value achieved).  

CODE APPROVAL and FIRE-SAFETY 

Open-cell and closed-cell SPF are both organically based materials and are considered combustible. Its use is specifically regulated in model building codes including the IRC under Section R314 FOAM PLASTIC, (under which a maximum flame spread index of 75, and a maximum smoke generation index of 450 is allowed). As noted above, the IRC requires that for all applications in habitable space and in most applications in non-habitable accessible building cavities, SPF must be protected by a 15 minute thermal barrier, as determined by ASTM E 119.   Exceptions allowing exposed SPF without a thermal barrier are delineated in IRC Section 314.5.3 Attics, and Section R314.5.4 Crawl spaces. In these exceptions where “the space is entered only for the service of utilities” (no storage or other ancillary uses permitted), the SPF must be protected by an “ignition barrier”, or if the specific foam and specific assembly has beenitested and approved under “NFPA 286 with the acceptance criteria of Section R315.4, FM4880, UL 1040 or UL 1715, or fire tests related to actual end-use configurations.”

 What this means is the product manufacturer or representative must have the specific-assembly tested and approved for a specific-application if the ignition barrier is to be avoided for attics and crawl-spaces, and for what thickness the material may be applied. Because all manufactures have not done the same testing, acceptable applications will vary from product to product, therefore neither ocSPF, nor ccSPF can be treated generically. Individual product Evaluation Service Reports (http://www.icc-es.org/Evaluation_Reports/index.shtml) must be obtained from the product manufacturer to determine if a particular unprotected application of its product is acceptable.

 POTENTIAL APPLICATIONS of SPF IN RESIDENTIAL CONSTRUCTION

 Once the physical attributes of the two SPF’s are understood, we can start to look at specific applications to assess the potential risks and what other building-envelope assembly factors need to be accounted for to obtain the desired result: a safe, durable, high-performance thermal envelope. Potential applications for SPF insulation include all aspects of the residential thermal envelope where more convention types of insulation are currently used. Among these are: 

 Frame wall cavities

 Sloped roof rafters above living space or unvented attics

 Ceilings below vented attics

 Foundations and below-grade spaces

 Band joists and mudsills

 Cantilevered framing and living spaces over unconditioned space

In addition, non-traditional applications of SPF may be appropriate where conventional types of cavity fill insulation are not. These applications include:  

 Auxiliary HVAC duct insulation

 Behind brick veneer

 Hybrid applications in combination with traditional insulation fill methods such as “Flashand- Batt” 

REGIONAL CONSIDERATIONS

 In combination with where in the thermal envelope the particular insulation is to be placed, the climate-zone where the subject building is to be constructed must be considered. For the purposes of this analysis, the main issues are wet versus dry, and hot versus cold. Dry climates, causing relatively less moisture loading on building envelope components than wet climates, are the less rigorous of insulation applications. Conversely, thermal assemblies in wet climates will be subjected to higher moisture loading and more rigorous moisture scenarios. Very cold climates, having the greater temperature gradient from inside to out (and therefore the greatest potential change in relative humidity for a given volume of air), present more challenging conditions than do warm climates.

We must also consider that the thermal and moisture driving forces are significantly different in cold climates versus warm climates. Assembly wetting and drying mechanisms will be different under peak load conditions, with warm climate moisture (generally) emanating from the exterior of the building and cold climate moisture emanating from the conditioned interior spaces.

Consortium for Advanced Residential Buildings

Steven Winter Associates, Inc.

SPECIFIC APPLICATIONS of SPF IN RESIDENTIAL CONSTRUCTION

The intent of this guideline is to provide usable, implementable information on acceptable uses of ocSPF and ccSPF in specific applications in residential construction. For that purpose, each of the above potential applications will be considered within a climate-zone context, and opined to be “preferred”, “acceptable”, or “not acceptable”. Each specific application and opinion of appropriateness will be followed by a brief commentary. 

SPF in Frame-Wall Cavities, Cold-Climates 

Open-Cell SPF: Preferred

Cold-climate use of ocSPF in frame wall cavities is an effective application of this insulation material with excellent air-sealing characteristics and reasonable R-value per inch. OcSPF is nearly always applied to full cavity depth: a 5-1/2” cavity providing approximately R-20. 

Critical Factors: Three critical factors need to be accounted for: interior vapor retarders; interior air sealing; and exterior vapor permeance. Contrary to some ocSPF manufacturers recommendations, interior finish-surface air-sealing and vapor retarders are critical to long-term durability and moisture control. High interior relative-humidity combined with pressure-drive and air-flow can cause ocSPF to become wet, even to the point of saturation. A vapor-retardant at the interior finish surface, such as vapor-retarder primer or multiple coats of latex paint will suffice. An exterior enclosure surface which is not vapor permeable will not allow drying to the exterior, potentially holding moisture gained from the interior. At least one reported moisture related catastrophic failure has been reported (in Northern Vermont) due to the combination of no interior air/vapor retarder and a moisture impermeable exterior.

 Closed-Cell SPF: Preferred 

Cold-climate application of ccSPF in frame wall cavities is an effective application of this insulation material with excellent air-sealing characteristics and high R-value per inch. Installed to full depth (5” in a 5-1/2” cavity) R-values would exceed R-30. More typical applications would leave a 1”-2” air space in the stud cavity depending on the R-value target for the assembly.  These wall systems would be neither air nor vapor permeable and would perform much like a polyurethane structural-insulated-panel (SIP). Due to its high cost per volume, most uses will likely continue to be a hybrid application such as “flash-and-batt” with a coating of ccSPF on the interior surface of the exterior sheathing, and the remaining cavity filled with fiberglass batt  insulation. Other insulation fill materials are also appropriate including blown-in-fiberglass or cellulose.

Critical Factors: Closed-cell SPF at typical thicknesses is a vapor retarder: Frame walls will not be able to dry effectively to the exterior. Because of this, a minimum thickness of 1-1/2” of ccSPF should be used in hybrid system applications. This will keep the interior surface of the SPF above the dew point in most climates, preventing condensation. In climates above 6,000 heating degree days, a minimum of 2” should be used. Additional SPF thickness may sometimes be required. A simplified hygrothermal calculation or equivalent should be performed during the design process to ensure the durability of the wall assembly. Like ocSPF, air-sealing and interior vapor control is essential with hybrid systems, however the thicker the foam, the less critical this becomes. Interior visqueen (polyethylene) vapor retarders should be avoided. Air-sealed and latex painted drywall is preferred. If required by code officials, variable permeance Class II vapor-retarders such as kraft-faced batts, smart membranes, or vaporretarder primers may be used.

SPF in Frame-Wall Cavities, Hot-Humid Climates 

Open-Cell SPF: Acceptable

The insulation levels provided by ocSPF are typically adequate to provide a high-level of thermal performance given the relatively low delta-T between inside and outside. Excellent airsealing capabilities can control air-leakage assuring that the insulation performs up to its potential.

Critical Factors: Open-cell SPF is moisture permeable, and in this potentially rigorous application, moisture flow must be controlled. Conditioned buildings in hot-humid climates require that the excessive interior moisture be removed by the mechanical air-conditioning system. This means the interior space will be dryer than the exterior and that the vapor drive through the thermal envelope is exterior to interior. If that flow is impeded by an interior-side vapor retarder higher relative humidity, potential condensation, and mold may develop. Exterior wall surface bulk-water and water-vapor control is also critical. It is possible that leaks and vapor pressure drive can wet the ocSPF assembly beyond the point the HVAC system can effectively dry it. In this climate, HVAC systems may not run enough to provide adequate dehumidification during shoulder months and may be turned off completely when “snow-bird” occupants head north for the summer. Brick-veneer siding installed over housewrap should also be avoided with ocSPF in hot-humid climates. Solar driven moisture (from wet brick) can be pushed into the frame cavity and overwhelm the drying capacity of the wall. Exterior drainage planes and bulk water management need to be well planned and executed.

 Closed-Cell SPF: Preferred

In hot-humid climates, the ideal scenario is effective air-sealing and moisture-vapor control at the exterior of the wall assembly. This is provided by ccSPF in both full R-value thickness or hybrid system installations. For flash-and batt, the thickness of the ccSPF application on the interior side of the exterior sheathing is not critical as in cold climates, but a minimum of 1” is preferred to achieve at least semi-vapor permeable status. The air-sealing, vapor control, and the high R-value of the “flash”, in combination with fiberglass fill provides a thermally efficient, forgiving wall system. Exterior drainage planes and bulk water management need to be well planned and executed. Unlike ocSPF, the ccSPF can provide a redundant moisture control layer keeping water out of the cavity in the event of a leak or drainage plane failure.

Consortium for Advanced Residential Buildings

Steven Winter Associates, Inc.

Critical Factors: Closed-cell SPF is vapor-impermeable at typical thicknesses. In hot-humid climates, interior vapor-retarders must be avoided. Otherwise a double vapor-retarder condition would result with the potential to trap moisture within the cavity. Because the impermeable ccSPF will be directly behind the exterior sheathing, if the sheathing gets wet from bulk water leaks, drying must be accommodated to the exterior. The drainage plane and siding assemblies must account for this.

SPF in Frame-Wall Cavities, Hot-Dry Climates 

Open-Cell SPF: Preferred

The insulation levels provided by ocSPF are typically adequate to provide a high-level of thermal performance given the relatively low delta-T between inside and outside. Excellent airsealing capabilities can control air-leakage assuring that the insulation performs up to its potential. 

Critical factors: Hot-dry is generally a forgiving climate in terms of moisture loading. Interior vapor retarders must be avoided none-the-less. Some hot-dry regions are subjected to periodic substantial rain events, such as El Nino, so exterior drainage planes remain critical. 

Closed-Cell SPF: Preferred

Closed-cell SPF in either full R-value thickness or hybrid system scenarios is highly effective in hot-dry climates. By providing air-sealing and redundant moisture control at the exterior and vapor permeance at the interior excellent air and moisture control may be provided.  

Critical factors: With the exterior vapor-retarder inherent to the ccSPF, an additional interior vapor retarder must be avoided. If the exterior sheathing does get wet though bulk water leaks or other mechanisms, drying must be allowed to occur to the exterior. The drainage plane and siding must provide for this.

 SPF in Sloped Roof Rafters

 Open-Cell SPF, Cold Climate: Acceptable

Open-cell SPF has a growing market presence in sloped roof applications in both sealed (unvented) attics, and with finished interior spaces defined by the roof slope (cathedral ceilings). Applying ocSPF directly to the sloped roof deck achieves the basic goal of both these approaches: providing full insulation at the roof deck, and blocking air-infiltration.

 Critical factors: The thickness of ocSPF allowed is dependant on individual manufacturer Evaluation Service Reports and varies between 5-1/2” and 10”. Even though the ocSPF is considered air-impermeable, it is not moisture-vapor impermeable. On the exterior roof deck, a vapor-retarder covering (such as Grace Tri-Flex 30) should be used, unless the roof surface is not moisture permeable, such as with standing seam metal. In cold-climates, interior relatively humid control is essential, or an interior-side vapor-retarder becomes critical in this application. If left exposed (unvented attic) a latex based vapor-retarder paint may be used. If covered by aceiling finish, the vapor-retarder may be the ceiling paint finish. Dependant on manufacturer, a thermal or ignition barrier may be required to cover the SPF. Roofs are rigorous-service assemblies and as such are more prone to failure than are walls. When leaks occur in ocSPF the material will become wetted, but will dry given time and dry conditions.  

Open-Cell SPF, Hot-Humid Climate: Acceptable

Same as above, except that a vapor retarder should not be added to the interior surface of the ocSPF. The exposed foam or its finish surface should remain moisture permeable to allowing drying to the interior. 

Closed-Cell SPF, All Climates: Preferred

Both unvented attics and cathedral ceilings can be accomplished with ccSPF. The high R-value per inch means required assembly R-values are achievable even given the limits to allowable thicknesses. As noted earlier in this paper, roof structure and wind-storm resistance are enhanced with roof deck applied ccSPF. Like ccSPF in walls, applications may be full depth, or a hybrid system augmented by a fiberglass blow-in blanket (BIB) system or Johns Manville Spider (self-adhered) spray fiberglass. Closed-cell SPF of at least 2” is not vapor permeable so in cold-climates a separate vapor retarder is not needed. As discussed in cold-climate framewall cavities, the ccSPF must be thick enough to prevent dewpoint condensation on its interior surface.

Critical factors: Dependant on manufacturer, a thermal or ignition barrier may be required to cover the SPF. Roofs are rigorous service assemblies and as such are more prone to failure than are walls. When leaks occur in ccSPF they may not be immediately apparent as the water will not penetrate the insulation. In the case of a catastrophic roofing failure, such as may occur in a hurricane, this can be a benefit. In the case of a worn roof, it will make the leak more difficult to locate.

 Ceiling below Vented Attic Space  

Open-Cell SPF: Acceptable

Although not a common application for ocSPF, insulating at the ceiling plane of a vented attic does provide a number of potential benefits. Air-leakage between the living space and vented attic is a commonly overlooked, and easy to rectify problem in typical building envelope. OcSPF can be very effective at providing the excellent air-sealing at this location. The R-value per inch is, however not much higher than far less expensive choices such as cellulose and fiberglass.

Critical factors: To be truly effective the ocSPF must seal at all ceiling penetrations like recessed electric boxes, fan covers, etc. Most ocSPF is not rated for such applications. Individual products will differ in their code-compliance. From a moisture and thermal viewpoint this is not a rigorous application, but in cold climates a vapor retarder should be included at the ceiling plane.

 Closed-Cell SPF: Preferred

Like ocSPF, placing full depth ccSPF at the ceiling plane of a vented attic is not a common practice. The use of ccSPF in a similar fashion to wall hybrid system applications does have major advantages. A thin coating of ccSPF will provide excellent air sealing between the vented attic and the conditioned living space. In combination with the latex painted ceiling, an effective vapor retarder assembly will be established, critical for cold climates.

Critical factors: For some ceiling penetrations a fire-stop rated ccSPF may be required. The two formulations are compatible so the critical spots may be coated first with the fire-stop, followed by the standard SPF for the rest. Blown in fiberglass insulation to a minimum 1.5” depth is considered an adequate ignition barrier by the IRC, so no other ignition barrier is required.

Consortium for Advanced Residential Buildings

Foundations and Below Grade Spaces 

Open-Cell SPF: Not acceptable

The moisture permeable nature of ocSPF renders it incompatible with the requirements of below-grade thermal insulation in many cases. Basement and crawlspace foundations are, essentially, holes in the ground with fail-proof moisture control measures very difficult if not impossible to implement. The presence of unintended bulk water may cause significant water absorption by the ocSPF. As a finished surface would need to be present covering the insulation, short-term drying would be impeded, leading to water-damaged finishes and other moisture related problems.

 Closed-Cell SPF: Preferred

Research on basement insulation systems by Steven Winter Associates and other organizations has concluded that the most consistently effective system places a water-tolerant insulation directly against the interior surface of the foundation walls. This accomplishes two major benefits: the insulation is air-sealed against the foundation wall so moist, interior air cannot come in contact with it, and condense out moisture; and the moisture resistant insulation is protected in case of unanticipated water entry. CcSPF can also be used effectively on the exterior of the foundation, but above grade covering remains a challenge.  

Critical factors: In basements, the ccSPF must be covered by an acceptable thermal barrier. In crawl spaces not used for storage, an ignition barrier may suffice, including an approved intumescent paint. For basement spaces intended to be finished, a 2” layer of ccSPF applied against the foundation may be followed by framing, additional batt insulation and gypsum drywall.

 Band Joists and Mudsills

 Open-Cell SPF: Acceptable

Perimeter band-joist locations where floor joists intersect the exterior perimeter are notoriously difficult to insulate. Typically, batt insulation is stuffed into the voids with no regard for airsealing or gaps. OcSPF provides a good  lternative at this critical area. Being a relatively small area, this is also an excellent place to use ocSPF where the budget is limited and less expensive insulations are called for elsewhere.

 Critical factors: Band joists between floors are most often concealed, so no other thermal barrier is required. For hot-humid, or extreme cold climates ccSPF is preferred to ocSPF in this application.

Closed-Cell SPF: Preferred

Perimeter band-joist locations where floor joists intersect the exterior perimeter are notoriously difficult to insulate. Typically batt insulation is stuffed into the voids with no regard for air-sealing or gaps. CcSPF provides an excellent alternative at this critical area. Being a relatively small area this is also an excellent place to use ccSPF where the budget is limited and less expensive insulations are called for elsewhere.

 Critical factors: Band joists between floors are most often concealed, so no other thermal barrier is required. The IRC also allows for ccSPF to be left exposed in basement and crawlspace band-joist applications in thicknesses less than 3-1/4”. Consortium for Advanced Residential Buildings

Steven Winter Associates, Inc.

Cantilevered Framing and Living Spaces Over Unconditioned Space

 Open-Cell SPF: Acceptable

This application is similar to a typical frame-wall application, though in a less rigorous configuration. Since there is no additional drainage plane to be concerned with, just a soffit or a ceiling below, the ocSPF can adequately meet thermal and moisture requirements under most conditions. Depending on the R-value needed the framing void can be completely filled or left with a void at the bottom.

 Critical factors: If a void is left in the assembly it must be at the bottom and not at the top against the conditioned space. In hot-humid climates a vapor-retarder should be employed below the insulation. Latex vapor-retarder paint will suffice.  

Closed-Cell SPF: Preferred

Closed-cell SPF may be applied in this location as either full depth, partial depth, or as a hybrid flash-and-batt type application. The ccSPF is applied against the bottom of the floor decking to a minimum thickness (see cold climate walls), or the cavity receives enough depth of material to equal the wall insulation R-value.

 Critical factors: With a partial-fill application, the SPF must be placed against the bottom of the floor decking leaving a void at the bottom of the assembly. The hybrid application requires that the remainder of the cavity should be completely filled with insulation leaving no voids (similar to walls).  

Auxiliary HVAC Duct Insulation

 Open-Cell SPF: Not acceptable

Providing HVAC ducts with additional levels of thermal insulation and air-sealing using SPF insulation is a relatively new technique in residential construction. The technique can provide substantial benefits when ducts are placed outside-of-condition-space, such as in attics, (a common installation). Attics can be harsh environments with large temperature swings and very high humidity, so additional thermal protection and decreased leakage can drastically improve HVAC efficiency.

 Critical factors: When placing HVAC ducts on the attic floor, placing SPF over them, and then burying them in loose fill insulation a set of very specific dynamics come in to play. Cooled air form the air-conditioning air-handler will be in the range of 50-55 degrees F. Attic air, during the cooling season will be very warm and potentially very humid. If the outside surface of the (cooling) ducts is below the dew-point, condensation will occur causing a moisture problem. If the SPF on the ducts is moisture permeable (ocSPF) the material would become wetted from the condensate, adding to the problem. 

Closed-Cell SPF: Preferred

The additional air-sealing and thermal protection provided by ccSPF to HVAC ducts placed on the attic floor and buried in loose fill insulation is substantial. The 2007 Supplement to the IRC (Section M1601.3) contains specific language pertaining to this application including limitations and required minimum ccSPF characteristics.

 Critical factors: There are two key factors which need to be accounted for in order to safely gain the additional thermal and air-leak prevention benefits: dew-point on the exterior duct surface, and vapor retarder placement. Under design conditions in hot-humid attics during peak cooling loads, the exterior surface of the insulation-buried ducts must be kept above the dewsS point. This means that the amount of insulation placed on them is critical. SWA  as determined that when using R-6 flex ducts, an additional R-9 (1-1/2” of ccSPF) for a total of R-15 will prevent the dew-point from being reached in nearly all typical conditions. The 1-1/2” of ccSPF is also an effective vapor retarder inhibiting moist attic air from penetrating into the insulation where the dew-point might be met.

 Behind Brick Veneer in Wood Frame, light-Gauge Steel, or CMU Construction

Placing one-inch or more of SPF over the structural sheathing or CMU surface within a brick veneer cavity can provide multiple benefits: Air-sealing, thermal break (especially over CMU or steel-studs), and drainage plane.

  Open-Cell SPF: Not acceptable

Open-cell SPF is not able to function as a drainage plane, but rather must be fully protected from bulk water and water-vapor loading. 

Closed-Cell SPF: Preferred

Several formulations of ccSPF are specifically designed for use as combination airbarrier/drainage planes in brick veneer applications. The closed-cell and continuous nature of the product is ideally suited for this use. Other similar systems rely on two-part applications such as a spray on drainage plane/air-sealant followed by rigid board insulation.

Critical factors: Not all ccSPF will be appropriate for this application; confirm specific product availability with individual manufacturers. For thermal performance and condensation control in cold-climates, a minimum 1-1/2” thickness should be applied. In regions over 6,000 heating degrees days, 2” minimum thickness is recommended.

 Limits of Liability and Disclaimer of Warranty:

Steven Winter Associates, Inc. makes no representations about the suitability of this document for all situations. The accuracy and completeness of the information provided by the author and the opinions stated herein are not guaranteed or warranted to produce any particular results and the advice and strategies contained herein may not be suitable for all applications. This document is provided “as is”’ without express or implied warranty. Steven Winter Associates, Inc. shall not be liable in any event for incidental or consequential damages in connection with, or arising out of, the furnishing, performance, or use of this documentation. The information presented in this article is for use with care by professionals.

© 2009 Steven Winter Associates, Inc.
All rights reserved.

A: To better understand why spray polurethane foam (SPF) is a viable solution for non-vented attic insulation in both hot and cold conditions, let’s take a look back at the origins and science behind the traditional vented attic.  Attics are vented to: remove moisture, reduce the potential for ice damming, and vent excess heat.

The basic idea behind code requirements for attic ventilation is to remove moisture-laden air that leaks into the attic from living spaces before it has a chance to condense on a cold roof deck.  Most homes have the living space insulated at the ceiling or attic floor level.  The roof deck, then, is cold because the insulation is on the attic floor and the attic space is exposed to outdoor air conditions.  Even with traditional cathedral ceilings, a one-inch air space is usually found between the top of the insulation and the bottom of the roof deck for ventilation.  In non-vented attics, the air space is not needed because the SPF creates attic conditions almost identical to living spaces.

Cold Climate Issues

Heat migrates from warmer areas to colder areas.  Warm air is lighter and more buoyant than cold air, and, as a result, in cold weather, the heated air inside your home rises into the attic via hundreds of attic bypasses or air leaks in your ceiling.  Attic by-passes — holes into attics such as can lights, wire and plumbing penetrations, and gaps between drywall and framing — are pathways for air (that you paid to heat or cool) to flow into attics.  Therefore, attic ventilation is supposed to provide a path for this warm, moisture-laden air outside before it can accumulate on the bottom of roof sheathing and cause moisture problems.

This air flow can cause other problems, too.  Ice dams occur when warm air ex-filtrating through attic by-passes warms the bottom of the roof deck. The snow on the roof melts and flows down until it freezes at the colder overhang area of the roof.  This ice slowly dams up, and water can work its way up under shingles, which creates leaks.

The bottom line is: To make a vented attics work, make sure you have enough ventilation equally distributed throughout the attic to remove moisture-laden air that may get into attics.

Today’s roofs are more complex and more difficult to ventilate well.  Homes today also are tighter and, therefore, have higher humidity levels than before.  High moisture levels can create mold and moisture problems in attics.  Ultimately, attic ventilation is oftern inadequate in solving moisture problems.  This is where a proactive approach on your part comes into play.

Spray foam insulation can be an effective solution in dealing with moisture issues in today’s roofs, as well as making a home more energy efficient.  SPF helps in the following areas:

1. Moving the insulation or thermal barrier from the attic floor to the toof sheathing creates a warm attic and a cold roof deck.  The result is that the bottom of the insulation is warm, and if you have enough insulation, there will be little chance of condensation on the exterior of the building.  In terms of condensation and heat loss, this is no different from an exterior wall.

2.  Often, duct work is lovated in attics.  If you have return air duct leaks in a traditional vented attic, you are drawing non-conditioned outdoor air into the HVAC system, which drives up heating and cooling costs.  With SPF, non-vented attics with insulation on the underside of the roof deck can turn the attic area into a conditioned space, thus reducing the negative effects of cold or hot air that is drawn into the HVAC system.

3.  SPF can reduce ice damming, which can help prevent warm air from coming in contact with the roof deck or sheathing.  this can substantially reduce — if not eliminate — the potential for ice dams.

4. When properly pretected against fire, SPF in a non-vented attic can create a semi-conditioned space that is more climate-friendly for treasured belongings.

5.  Closed-cell SPF greater than about two inches (5.1 cm) thick is a vapor retarder with a permeeance rating less than one perm.. Any moisture in the attic space stays in a vaporous state and can’t diffuse through it.  With traditional insulation, air easily blows through insulation.  As it does, it scavenges away heat and reduces its effective R-value.  This wind-washing should not degrade the R-value of SPF.

No matter what type of attic you have or insulation  you choose, it’s always important to control the moisture at its source.  Most moisture in homes comes from baths, kitchens, and humidifiers.  The use of bath fans with controls that automatically run for a preset time may help to ventilate excess moisture.  Also, instructing homeoweners not to over-humidify their homes can be beneficial.  In cold weather, the indoor relative humidity shouldnt reach above 40 to 45 percent.  Some health experts recommend that humidity not get about 30 to 35 percent.

Warm Climate Issues

In warm climates, vented attics termperatures can easily reach 140 °F (60 °C).  Many attics have return air ducts, which draw this hot and often humid air into the HVAC system.  The result is higher air conditioning costs.  It takes a lot more energy to cool 140 °F (60 °C) air than 90 °F (32.2 °C) air.

Non-vented attic spaces insulated with spray foam, on the other hand, are going to be cooler than attics insulated with other products.  This is becuse SPF attics will essentially be the same temperature as the indoor air.  Un traditional ventilated attics, the relative humidity in the attic is the same at the outdoor relative humidity.  Surface relative humidity greater than 70 percent is more conducive to mold growth.  Non-vented attics insulated with SPF would have lower terperatures and humidity than attics without SPF.  They are also tighter and, as a result, have less air infiltration by warm, moisture-laden outdoor air.

Additional Benefits

Closed-cell SPF has been proven to increase the up-lift or blow-off resistance of roof decks.  This is of value in storm-prone areas.  Dr. David PRevatt at teh University of Florida conducted research that shows that closed-cell  spray foam sprayed to the underside of roof sheathing will effectively bond the roof deck to the roof framing.  He found that spraying three inches of foam created a 300 percent increase in uplift resistance.

Both open- and closed-cell spray foam can be useful products for non-vented attics.  An advantage of closed-cell foam in non-vented attics is that it absorbs negligible amounts of moisture and acts as an air barrier.  Closed-cell SPF has been used on commercial roof decks for 50+ years with great success.

However, under a sloped roof deck, insulation can raise the temperatures of shingles.  There have been several studies that show this increase in temperature ranges from 2 °F (-16.6 °C) to 7 °F (-13.9 °C), depending on the location.  While increased surgace temperature can decrease the life of asphalt shingle roofs, the increase in shingle temperatures caused by non-vented attics may only decrease the service life by five to 10 percent.  This cost should be wighted against the energy savings provide by non-vented attics.

These studies also show that other more significant factors affect shingle temperature and service life, including  solar exposure and roof color.

Contractors should always discuss the shingle warranty witht he homeowner and builder before applying SPF under a roof deck.

Tips for success:

1. Make sure the surfaces are dry.  SPF will not adhere to wet or damp surfaces.

2. Use iginition barriers as required by codes.

3. Ensure applicators are properly trained and have experience with spraying non-vented attics.  Retrofitting existing attics with SPF requires extra safety considerations for the contractor.

By Steve Easley, Owner of Steve Easley & Associates Inc.

Steve Easley has specialized in helping builders reduce construction defects, reduce call-back costs, and refine construction practices for over 30 years.  He was a professor of building construction a nd contracting at Purdue University 10 years, where he received severeal teaching awards.