Spray Foam Attic Insulation

I had photos, but for the very first time I inadvertanly deleted all images by adjusting the formating, from my morning water intrusion investigation. Another lesson learned. Anyway, the attic was recently spray foamed completely covering the underside of the roof and gable ends except for the gable vents. The foam is about 6 inches thick. In my opinion, covering the sheathing and rafters is not acceptable due to inadequate ventilation for the roof covering. Any opinions related to the use of spray foam? :neutral:

There should be NO ventilation with this insulation. The attic is considered conditioned air space. The entire attic should be enclosed. To include any access panels. Google Icynene

Here we call it a “hot roof”. Works quite well, I have seen alot of this application. I do believe that it must be a closed cell sprayfoam, or an open cell sprayed to certain thicknesses can create an air barrier as well.

Difference between open and closed cell? Is there a visual difference? No impact on roofing warranties?

Mr. Evans,

Here ya go


If it is open cell and in a cold climate, then the interior humidity must be kept under control or it be sprayed/covered with an air/vapour barrier.

Energy Design Update had an article a few years back about a small house in upstate New York, I believe, that suffered severe moisture problems/beginning rot 3 years after construction. It was sprayed with a popular brand name open cell foam and had poor interior house ventilation.

To clarify: The attic floor was insulated with standard fiberglass batt insulation. The roof structure including gable ends, minus cable vents, was completely covered with the foam. Could not see any rafters as they were covered. This system reverses the traditional attic/roofing ventilation requirements. How is the sheathing going to “breathe”? We have been told thhat even a second shingle layer impacts roof expectancy, this seems to be far worse than a two layer roof. How are roof leaks going to be detected?
I did manage to take the two thermal images, as I lost the digital images. :neutral:

In most cases rafters are sprayed with open cell. Open cell foam will allow trapped water/moisture to pass through. Ultimately revealing a water stain.

I would think that this open cell consideration would be important for leak detection.


Ventilation is not required for the sheathing’s ability to breath, it’s simply required so the asphalt roof shingles do not rapidly deteriorate from a hot 130 F. attic cavity space.

When a spray foam insulation is applied to the roof sheathing (which is highly recommended for newer tighter homes), it now insulates the attic space from the extreme 130 F heat that once radiated right thorough the hot shingles and roof sheathing. The severe attic temperatures no longer exist in the attic space with spray foam insulation application. It now acts as a barrier so the hot sun will not radiate into the attic cavity and affect the underside of the asphalt roof shingles.

In short, the attic now becomes a “conditioned” space of the house that is just as comfortable as any other room in the home.


One of the problems with spray foaming the rafters of an existing building is the size of the air conditioning unit(s). If the units were properly sized for the old insulation method (and their ability to rid the house of moisture) foaming the roof will actually allow for a smaller A/C unit. Too large a unit (the original?) may have difficulty removing the moisture. New foam insulation contractors need to work closely with the HVAC technician and they do not!

More Info
http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation/?searchterm=uninsulated attics


Thanks for all of the very good information. The foam attic insulation must not be a common installation in my area. It is sometimes difficult to change the thought process, after reading so much information regarding the need for proper attic ventilation. I know that 99% of my inspections will still require evaluation of adequate ventilation with standard insulation. If I ever encounter the foam again, at least I will have a better understanding of the requirements. :stuck_out_tongue:

John - To me this is an improper installation and one that I have not seen at all. I only see it here in Florida and there is NO insulation on the rafter and spray foam. There is ABSOLUTELY no ventilation and the house is SEALED. I am saying I have seen about 500 homes with this foam and most here is Icynene. NONE of them have been installed in this manner that you state.

My report would state that this is an unorthodox manner of installation and to have the proper licensed tradesman evaluate the installation and determine if the process is correct or not and to fully document it for the future owners reference.

CYA - I would note it and defer to having a properly licensed tradesman evaluate the installation and determine if the process is correct or not and to fully document it for the future owners reference.

I did refer out in the report. Thanks.

Looks improper to me. If they were trying to create a conditioned attic, they got it wrong. They now have two building envelopes and a recipe for condensation problems.

For conditioned attic, there must be no attic ventilation, air impermeable insulation must be applied directly to the underside of the roof sheathing, there must be NO vapor barrier between the attic and the living space (e.g., kraft backed fiberglass on the ceiling), insulation must be thick enough to maintain monthly avg temps of at least 45 degrees F on the condensing surface (underside of the foam) in your area.

Requirements are laid out in IRC 2006 R806.4

Yes leaks are hard to find - the insulation manufacturer’s say that it minimizes interior damage due to leaks.

This is a new system and is not yet fully time proven. It will be interesting to see what the future holds when reroofing of a large percentage of these is done. That installation you described is wrong, in my opinion, unless the home is constructed with the intent to install this insulation system retrofitting it in is gonna be a mistake.

I have applied Polyurethane Foam closed-cell insulation materials. It’s materials offer high R values, one can use a thinner foam board to have the required thermal resistance one desires. This can be extremely helpful if there are space limitations involved. This strength involved the ability of the foam to resist deformation and the ability to main its shape when forced or loaded down.It can handles a wide temperature range, which makes it effective as a roof insulation. When combined with laminated aluminum foil facing, it is also an effective moisture and vapor barrier.for the last 10 years faced no problem at all.