Spray Foam Myths Debunked: Spray Foam causes moisture problems in the roof line

June 30, 2017 Anthony Naimo

As one of the most quickly adopted high-performance building materials available in the market, there has been a lot of noise made about spray foam insulation and its performance ability.  Much like the concern about fake news found on social media channels, noise about building materials such as spray foam insulation can create confusion among builders, architects, building owners and even, regulators. Reliable information from reliable sources, such as directly from spray foam manufacturers or from respected industry publications, allows the aforementioned individuals to make informed decisions about the materials they use in their buildings with confidence.

Icynene’s Building Genius will explore several myths about spray foam insulation that are being misrepresented as truth and help you separate fact from fiction.

Think spray foam insulation causes moisture problems or that spray foam can cause shingles to deteriorate?  In fact, spray foam insulation can help avoid problems like these.

Spray Foam Myth:  Insulating with spray foam insulation at the roof line will cause moisture problems with the roof sheathing.

In an unvented attic scenario, to limit air leakage as well as any associated condensation at the roof line, a continuous air barrier is required.  In colder climates, a Class II vapor diffusion retarder may also be required on the interior to help limit vapor diffusion. Spray foam insulation is considered an air impermeable insulation material due to its ability to insulate and air seal in one step. Air impermeable insulation can actually help protect the sheathing from damage.

When considering how to insulate an unvented attic, spray foam insulation does not necessarily have to be used. However, if spray foam insulation is not used, then certain aspects have to be considered to compensate such as:

  • How will the traditional insulation (as well as other elements) be secured in place in an unvented attic assembly?
  • What supplemental air barrier will be used?
  • What about diffusion vents?
  • How will attic ventilation be achieved?

Conventional, vented attics have their own set of problems too, including:

  • Attic floor can have numerous penetrations that are not air tight
  • Ductwork and mechanical equipment in the attic can contribute to  any air leakage and heat transfer issues
  • HVAC systems operate in adverse conditions and, as a result, are far less efficient than they should be. The graphic below shows how the HVAC equipment is operating in a hot 135°F attic. The continual operation of the HVAC equipment in a hot attic like this as it tries to maintain a comfortable temperature in the living space below leads to accelerated wear and tear on the equipment and limits its ability to function efficiently thereby adding to higher heating and/or cooling costs.
  • Venting has to be provided to help control moisture and other associated problems

Conventional vented attics have their own set of problems

When trying to address these problems, spray foam insulation as an insulating and air sealing material can help prevent them from occurring.

Icynene’s Building Science and Engineering experts can work with you to understand how spray foam insulation can be integrated into your current and upcoming residential and commercial projects, and help debunk the myth that insulating with spray foam insulation at the roof line will cause moisture problems at the roof sheathing.  Be sure to catch the next debunked spray foam myth on Icynene’s Building Genius blog. 

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