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Spray Foam Benefits by RLC Engineering

Opinion paper on the benefits of Spray Foam Insulation by Craig DeWitt, Ph.D., PE of RLC Engineering LLC

Monday, October 30, 2017

What is this opion paper about?

The opinion paper is a 3rd party opinion paper written by Craig DeWitt, Ph.D., PE of RLC Engineering LLC discussing the benefits of spray polyurethane foam insulation. Topics covered:

  • Structural Benefits
  • Thermal and Air Benefits
  • Roof Benefits
  • Crawl Spaces Benefits

Below you can read excerpts from each section. You can download the full paper at the bottom of this page.


Expanding spray-in-place foam insulation products such as those based on a polyurethane formulation have several beneficial aspects over other forms of insulation. Spray foam insulation currently costs more than alternative insulation products, but this additional upfront cost can be overcome when the other benefits of spray foam are utilized and realized. These aspects include benefits associated with increased structural/strength properties, enhanced thermal insulation capabilities, and reduced air infiltration properties.

Structural Benefits of Spray Foam Insulation

Clemson University has been researching the use of spray foam as an enhanced attachment system for roofing. This research centers on how to retrofit or construct buildings to be more resistant to hurricane and other high wind events. Clemson’s research shows that spray foam can significantly improve the attachment of roof sheathing to trusses and rafters, similar to the way construction adhesives help bond a floor system together. In a retrofit case, foam can be sprayed on one or both sides of the sheathing/rafter intersection from inside the finished roof. In new construction, spray foam can be applied to the entire roof system. The spray foam makes a significantly stronger roof than either nails or screws alone.

Thermal and Air Benefits

A second aspect of spray foam is the enhanced thermal insulation characteristics. The stated R-value, or thermal resistance value, of insulation is measured under laboratory conditions. Real-life in-use R-values are quite different. An R-13 rated insulation batt installed improperly may only provide R-9. Whole wall Rvalues may be even less because of voids, wood, headers, etc. in the wall. Spray foam can provide a higher whole-wall R-value because of its ability to better fill wall cavities around electrical, plumbing, and other obstructions within the wall. The Oak Ridge National Lab has tested several whole-wall R-values for various wall/insulation combinations...

Typical loose fill or batt insulation works well if installed correctly, and if installed in conjunction with an air barrier. Good installation is difficult to do, however. The insulation is often packed too tight or too loose, cut too short or too long, gapped around plumbing and wiring, or left out because of access problems.

Spray foams claim a couple benefits. First, they fill gaps and voids better. Second, they perform well as air flow retarders. The result is a higher in-the-wall R-value. Infiltration is also reduced, so that component of a building’s energy use is reduced. Both of these benefits result in raising the "effective" R-value of spray foam when compared to typically installed loose fill or batt insulation.

Roof Benefits

Insulating the underside of a roof rather than a ceiling creates many other benefits as well. Historically, we ventilated roofs in an attempt to prevent moisture problems and reduce heat build-up.

Current research shows that much of the moisture in attics comes from damp basements or crawl spaces, as well as from the living space. Research also shows that if we address crawl space, basement, attic and living space moisture, we do not need to ventilate an attic. In fact, by ventilating an attic, we can often make a moisture problem worse...

In a standard insulation system, ceiling insulation reduces the transfer of heat from the attic to the living space (in the summer). Attic temperatures can often approach 140F during the day. Most of this heat enters the attic space through a multi-step process. First, solar energy warms the shingles and sheathing. The hot sheathing then transfers heat to the rest of the attic through conduction, convection and radiant heat transfer. The 140F temperature of the underside roof surface drives the heat transfer process

By insulating the roof surface with spray foam, the surface temperature exposed to the attic (the temperature driving the heat transfer) is reduced by as much as 40F.

The benefits of including the attic in the insulated space are:

  • Duct leakage and heat loss/gain from ducts is much less of an issue
  • Air sealing is easier in the roof that in the ceiling
  • Dust and loose insulation are less likely to migrate down to the living space
  • Tests show energy costs are lower when the attic is sealed

Crawl Space Benefits

Batt insulation is usually installed between the floor joists over a crawl space foundation. Problems associated with this installation technique include incomplete thermal barriers from obstructions such as wiring and plumbing, ductwork, and narrow or wide joist spacing. Batts are often compressed during installation due to the use of wire insulation hangers. Open web floor trusses create additional problems in that the open webs create pathways for air to move around the batts. During the summer, warm humid air can flow around the batts and create condensation, mold and decay problems in the floor system. In my opinion, open web floor trusses are impossible to adequately insulate with batts.

The full opinion paper by Craig DeWitt, Ph.D., PE can be downloaded below.

Download Benefits of
Spray-in-Place Polyurethane Foam Insulation

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