Spray Foam Attic Insulation

[John Evans]

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?

[Russell J. Hensel]

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

[Rodney Misener]

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.

[John Evans]

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

[Jeffrey Moore]

Mr. Evans,

Here ya go

http://www.foam-tech.com/products/ur...losed_cell.htm

[Brian A. MacNeish]

Originally Posted by rmisener

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.

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.

[John Evans]

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.

[bdoles2]

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.

[Larry D. Kage]

Originally Posted by bdoles2

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.

[David P. Valley]

Originally Posted by jevans

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.

Attachment 35077

Attachment 35078

John,

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.

[rspermo]

John,

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!

[Roy D. Cooke, Sr]

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

http://forums.jlconline.com/forums/s...ad.php?t=31050

[John Evans]

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.

[Russell J. Hensel]

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.

[Merwin T. Scruggs]

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.