Building Science

Additional Applications

Benefits – Residential and Commercial

Sprayfoam allows for lower construction costs, it meets and generally exceeds today’s building code requirements, and provides your customers with the benefits of spray foam.

Likely Lower Construction Costs

Spray foam acts as both insulation and an air barrier that seals the building envelope, reducing the need for additional air sealant materials. You can also reduce your framing costs due to the higher R-values of Spray foam over fiberglass. Also, some jurisdictions require air tightness tests to prove compliance. A spray foam building assembly can be tested before the drywall is applied, which could save you time and avoid costly repairs if defects are found.

Meet or Exceed Building Code Requirements

States and localities continue to adopt codes that encourage or mandate increased energy efficiency. Spray foam insulation can help you meet or exceed the 2015 IECC energy codes.

Performance vs. Prescriptive R-values Let us show you how to correctly design the HVAC system with a spray foam envelope and save you and your customers money while providing a better product!

Provide Your Customers with the Benefits of Spray Foam

Whether it’s a home or office building, strip mall or corner store, building managers and owners are concerned about building performance and energy efficiency. Spray foam can help you provide long-term value to your customer. With spray foam, your customers can enjoy the benefits of spray foam insulation including energy efficiency, increased structural integrity, pest resistance, leak-resistance and draft-free homes or buildings. Spray foam is an excellent way that you can provide energy reductions to your customers.

Building Science

Ducts in Conditioned Space

The location of the duct system can have a significant impact on the overall performance of the system–both the utility use and the ability to provide comfort. The energy loss from the ducts for forced air heating and cooling systems can be significant, depending on the location of the ducts, and how well the ducts are sealed against air leakage. Though it is conceptually easy to imagine sealed duct systems, tight duct systems are unfortunately all too rare - duct leakage values of 20% of system flow are common. In many houses, the distribution duct work is located either in a vented crawlspace or in a vented attic –effectively outdoors. With the ducts located outside of the thermal envelope of the home, any leakage and conductive losses from the duct work is lost directly to the outside. Even worse, whenever air is leaking out or the ducts due to the system running, air is coming into the house to replace the lost air—resulting in forced air leakage whenever your furnace or air conditioner runs. Moving the duct work and air handlers inside the thermal enclosure can be used to help prevent this energy loss to the exterior. Alternately, the thermal enclosure can be extended to include areas such as crawlspaces and attic as part of the conditioned space of the house. In general, the placement of the mechanical equipment will depend on the design of the house. For houses with conditioned crawlspaces and basements, it is often logical to place the air handler or furnace in those locations. For slab on grade designs or elevated floors, available space can become a limitation. In these cases, unvented conditioned and semi-conditioned attics provide for a convenient location for the mechanical equipment and ducts. Otherwise, the equipment and / or ducts can be located in a dropped ceiling or in closets.

This Information Sheet has been prepared by Building Science Corporation for the Department of Energy’s Building America Program, a private/public partnership that develops energy solutions for new and existing homes. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

For more information about Building America go to

Venting and shingle temperature. It's a common misconception that code-required venting significantly lowers the summer temperature of the roof surface. In fact, tests have shown that it lowers the surface temperature of asphalt shingles by at most about 5°F.

For many years, roofing manufacturers required that shingles be installed over vented substrates, but today, several companies — including Elk and CertainTeed — will guarantee shingles installed over properly constructed unvented roofs.

High Performance Housing — FAQ

2009 IRC

Conditioned Attics

Q: I want to make my attic into living space by moving the insulation to the underside of the roof deck between the joists? How do I meet the roof venting requirements of the building code if I do this?

A: There are two ways that this can be accomplished:

  • A ventilated roof assembly
  • An unvented attic assembly (a.k.a. “compact” assembly or “hot roof”)

Ventilated roof assembly

You can insulate the rafter space provided that you leave a ventilation space between the top of the insulation (typically fiberglass batts or blown cellulose) and the underside of the roof sheathing ( Section R806.1 Ventilation required ). The minimum net free area of the ventilation space is described in Section R806.2 Minimum area and Section R806.3 Vent and insulation clearance .

Figure 1: Vented cathedral roof assembly

In practical terms, one of the issues is to ensure a continuous ventilation channel along all rafter bays, from eave to ridge (or roof-wall interface). This is especially challenging at roof interruptions such as skylights, dormers, or hip rafters (in hip roofs).

In addition, maintaining an air barrier between the interior and the ventilation channel is critical. In cold climates, air barrier failures here can result in condensation damage, ice damming, and increased energy use.

Unvented attic assembly

Alternately, an unvented attic assembly can be implemented, based on the requirements of Section R806.4 Unvented attic assemblies . This section was originally appended in the 2007 Supplement to the International Residential Code (IRC).

The underlying goal behind this section is to raise the temperature of the cold-side inner surface (i.e., underside of the roof deck, or inner foam surface) sufficiently that condensation will not occur, if interior air comes in contact with that surface.

This is done by using what is referred to as “air impermeable insulation,” such as rigid foam board or spray foam.

Two acceptable assemblies are shown below: one with air impermeable expanding spray foam insulation installed at the underside of the roof deck (as shown in Figure 2), and the other with rigid board foam plastic insulation installed above the roof deck (as shown in Figure 3).

In both assemblies, air permeable insulation (such as batt or loose fill) is used to increase overall insulation value. This is by no means a requirement; however, it is typically the most economical way to achieve target (or code minimum) R-values. Alternately, “air impermeable insulation” alone could be used for the entire insulation thickness, assuming that all requirements below are met.

Figure 1: Vented cathedral roof assembly

Figure 2: Spray foam unvented roof assembly

Figure 3: Rigid board foam unvented roof assembly

High Performance Housing FAQ

In the assembly shown in Figure 3, a structural nail base would typically be required over the rigid foam for a roof cladding such as asphalt shingles.

The minimum required thickness of the “air impermeable insulation” is stated in Table R806.4 Insulation for condensation control , which provides prescriptive requirements for minimum rigid board or air impermeable insulation R-values based on climate zone, in order to manage the condensation potential in the assembly.

Several other key requirements of R806.4 are as follows:

  • If wood shingles or shakes are used, a minimum 4” vented air space must be used between the shingles/shakes and the roofing underlayment (R806.4.3).
  • In climate zones 5 through 8, the “air impermeable insulation” must be a vapor retarder (Class II; 1.0 perm dry cup or less), or have a vapor retarder coating or covering in direct contact with the underside of the insulation. For instance, an air impermeable but vapor permeable spray foam (0.5 pounds/cubic foot) would not meet this requirement, unless a vapor retarder coating were applied (R806.4.4).

Applicable Code Sections

2009 International Residential Code for One- and Two-Family Dwellings

  • R806.1 Ventilation required
  • R806.2 Minimum area
  • R806.3 Vent and insulation clearance
  • R806.4 Unvented attic assemblies
  • Table R806.4 Insulation for condensation control

Figure 4: Table of minimum rigid board/air impermeable insulation per climate zone

Conditioned Attics 2 of 2

This Information Sheet has been prepared by Building Science Corporation for the Department of Energy’s Building America Program, a private/public partnership that develops energy solutions for new and existing homes. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

For more information about Building America go to

Additional Applications

Pole Barns

Sub Slab or under slab

Storage Tanks

Slab Jacking

Foundation Restoration/ Repair

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