Extra Attic Insulation...Is it Wrong?


Old 03-17-03, 07:28 PM
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Extra Attic Insulation...Is it Wrong?


I have a typical ranch home with fiberglass batts in the floor of the attic. I would like to increse the R-value in the attic, but would prefer not to add insulation to the floor of the attic.

Is there anything wrong with insulating the underside of the roof in the attic just as if it were a cathedral ceiling...As long as I provide for sufficient airflow betwen the insulation and the roof, and add some soffit vents where possible? I have a ridge vent and gable end vent for ventilation.

Any information would be appreciated!
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Old 03-17-03, 08:48 PM
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Insulating between conditioned and unconditioned spaces.

The insulation in the attic floor is defined as part of the thermal boundary of the home. Whereas the roof and the attic space are considered to be 2 unconditioned spaces. There are no thermal benefits to insulating the underside of your roof. There is a disadvantage to doing so. That is the insulation will retain heat, especially during sunny days. This will impede the way the roofing materials expel heat and moisture. In other words the insulation applied to the underside of your roof will accellerate the deterioration of the roofing materials, such as your shingles, underlayment and even your rafters. This also explains why roofs belonging to cathedral ceiling do not last as long as regular roofs, even with adequate ventilation. The average difference is approximately 15 years. Heat deteriorates roofs and the greater degree of heat, the greater degree of deterioration. It is unwise to insulate the underside of a roof of an unfinished attic because of the aforementioned, coupled with the fact there is no thermal advantage towards the structure.
Old 03-18-03, 05:18 AM
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Thank you very much for the info. Your explanation makes a ton of sense and clears up a lot of confusion that was going on in my head.

Thanks again!
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