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Icynene Insulation

Neal Lewis

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This is the first time I have seen icynene insulation installed covering the entire roof deck and raming. The only venting at the gables were blockedoff completely and the side walls were covered with icynene. Only a thin layer of original insulation in the attic floor. Not sure about a vapor barrier.

Inspected the house lastweek and did not notice any moisture. Was in the attic today to check the A/C and there was a definite smell of moisture/mildew or something. Bathrooms have exhaust fans discharging to the exterior. No moisture in house and oly a minor puddle in the basement after the 8 inches of rain a week ago.

I have tried to research this type of installation and have found nothing negative about it. What is your opinion about covering the wood and zero ventilation? Thanks

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Like any engineered material, there are a lot of "if's", meaning if all the installation criteria are met, it does not need ventilation.

It does need a Class II vapor retarder. Practically speaking, that's drywall properly detailed & installed, a coat of sealer, and 2 coats of low perm paint (I think I got that right). Roofing, siding, and all other building envelope waterproofing details need to be installed properly.

Go to http://www.buildingscience.com and download "Vapor Barriers and Wall Design". After that, download and read BSD-106 Understanding Vapor Barriers (just recently updated). It's required reading before one can understand any of this stuff satisfactorily.

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Originally posted by Scottpat

A problem with Icynene is that it covers everything and if you do have a water leak they are most difficult to find. With the musty smell, it sounds like you could have a leak in the attic.

Or they may have created a nice tight home but didn't bother to do anything to balance the humidity in the home and now excess water vapor that used to diffuse into that attic and got carried away by the attic vents is now becoming trapped in the attic.

Icynene is permeable but remember it's intended to be an air barrier. Without some means to balance that interior atmosphere, moisture will build up on the interior faster than it can diffuse through the shell and they could end up with musty conditions.



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