A newer approach that appears to be rarely used around here (Green Key Village notwithstanding) is to apply spray foam (either open or closed cell) insulation to the underside of the roof sheathing. I opted for this approach in a previous home. The attic is then sealed and doesn't require ventilation. There is no additional insulation on the floor of the attic. Typically, the attic will be no warmer than 10 degrees higher than the living spaces of the house. With this approach, you essentially reduce the amount of heat entering the structure. It effectively acts as a radiant barrier also as the roof sheathing is not presented to the attic as a hot, long wave radiation source. There are a couple of downsides. With the closed cell, you may not know about any roof leaks until a substantial amount of damage has been done. Also, the foam is created by the chemical reaction of two materials (mixed at the hand sprayer) and any malfunctions could leave you with an uninhabitable home. It is best done during the original construction of the house (that is I what I did) as a retrofit may be difficult and/or expensive.
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Originally Posted by DangeloInspections
Great topic.
There are different opinions on this, but for the record, I have taken many classes on the subject, and have no ulterior motives here. I am not selling anything.
I'll try to keep this brief, but as a person who is in over 400 attics a year inspecting, I will share with you my views.
The newer homes have radiant barriers installed on the underside of the roof sheathing during construction. That is fine and does help. Cost increase in minimum and it does not disturb the insulation, etc.
Aftermarket radiant barriers are cost prohibitive. Engineers say that at best you may save 5-10% on your electric bill. Often, portions of it fall down after a few years. If the top of it gets dusty, (and it will) you will lose effectiveness. Basically not recommended. Very long payback time, if any.
You would be better off after having everything you want done aftermarket in your attic, (solar tubes, can lights, etc) adding another 4-6 inches of insulation to go from an R-30 to at least an R-38.
The experts views on attic insulation and ventilation are changing everyday. I believe that ten years from now you will see big changes on how we handle both in a new home.
Frank
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