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Improving ventilation/insulation in existing finished attic

Improving ventilation/insulation in existing finished attic


Old 10-23-01, 06:34 AM
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I recently moved into a 1922 2-1/2 story colonial in Baltimore, MD (hot, humid summers and fairly cold winters). The previous owner did a poor job of insulating when he finished the attic this past year; he stuffed R-19 faced fiberglass between the 2x6 rafters directly against the roof sheathing and covered it with drywall (the FG facing is correctly placed to the inside). There is no venting at all in the attic - the roof is a "hip roof" (?) with no gable ends and has a large dormer on each side. This summer, temperatures in the attic were stifling, even with the A/C running full bore, and I am concerned about moisture problems in the winter. The problem is the room design is very complex and I do not want to take down the existing drywall as this would be a monstrous undertaking. I have consulted many sources for advice, including two local insulation contrators. The first contrator visited my house and said I basically could do nothing, and that he didn't think I would have a problem with roof rot. The second recommended pumping PolyMaster plastic foam to completely fill all the void cavities between the existing fiberglass insulation and the roof sheathing, including over the eaves and to the roof peak, basically closing off all air gaps between the the roof and the finished room. The thinking is that the foam will both prevent moisture from reaching the roof in the winter and will prevent superheated air from being trapped against the roof in the summer. The cost would be $1800, which seems very expensive, and I have not seen this practice suggested anywhere else. Does anyone have any recommendations on:

1. Will foaming in against the roof solve the problem (cost not withstanding), that is protect against winter moisture and summer heat build up?
2. Are there any other possible solutions? My top choices have been to either leave it alone and take my chances, or to try to cut a hole in the drywall between each rafter and try to shove something (PVC, etc) between the FG and the roof to add an air gap, then install continuous soffit and ridge venting. This would greatly compress my existing insulation and minimize its effectiveness.
3. Could I paint the ceiling with a type of paint that would prevent moist air from penetrating the drywall/FG and reaching the roof in the winter? Although the insulation is faced, from what I can see the previous owner did a poor job and left some gaps.

Sorry if I was long winded, but I have researched long and hard on this issue to no avail. Please help!!!

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Old 10-24-01, 03:13 AM
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Sounds pretty complicated to me...

I can't figure how he got the drywall in the attic to install on the underside of the roof rafters...

So I assume that there is a large access hole or doorway. and that most the attic is walkable.

If so even though it is a big undertaking, I would remove everything he has done.. The foam idea sounds kind of iffy to me and for a lot less than 1800 dollars I would assume you could have the installed fiberglass and sheet rock removed by a contractor..

As for creating venting behind the installed fiberglass by cutting holes in the drywall.. I would think this would be next to impossible..You will find it very hard to slide anything along that area to create a void for air flow..The biggest problem is going to be all the roofing nails sticking through will restrict anything from sliding easily.. It is a theory that if the entire cavity is completely filled with insulation fiberglass or cellulose that condensation will not occur... I believe that venting is always best.

Blown in Cellulose or Fiberglass R-38 runs about 80 cents a square foot in this area..S.E. Michigan

Good Luck

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