Replacing roof - vent or not vent? I'm SO very confused

ctaylors6May 31, 2009

We are about to replace our roof. We live in Dallas and our A/C bills are huge for several months of the year. In conjunction with the roof replacement we want to insulate our attic. It currently has about 6" of loose insulation on the floor. There's nothing on the rafters or on the walls. It's a standard gable shape with one dormer. There are currently 2 triangular gable vents.

The house is brick on the first 2 floors; wood siding on the gables and dormer.

The attic has 2x6 rafters. No trusses, just a handful of collar ties (I think that's correct term) pretty near the top of the roof.

The A/C and furnace for the second floor are located in the attic, as is all the ductwork for the 2nd floor. The ducts are very old flex kind, probably needs to be replaced. We can't relocate any of the HVAC equipment or ducts to another floor.

We'd like to finish out the attic in 3-5 years. We've had contractors tell it's definitely feasible. The ridge is about 10.5 feet above the floor, and the roof is fairly well steeped. The attic floor is about 34' x 37'. (We've checked floor strength and space for stairs). We just can't spend that kind of money now to finish the attic. So for now, we just want to make sure we take that (the future attic finish) into consideration when we insulate now.

Finally, we're happy to replace the siding and insulate the attic walls (basically the gable and dormer walls). There's a visible crack between the top of the brick and the bottom of the siding. Kinda scary how there's so little insulation and protection from the elements. The buckets help with the rain.

I've read tons of information on roofs and insulation this weekend, including several things in Building Science. I'm so confused about what to do with the roof. Should we plan on putting in a great soffit/ridge venting system and then leave about 1" of air space then insulate then drywall? Or should we have no venting and just spray everything with closed cell foam (or other foam spray)? It's very hot and humid for half the year, but it does ice/snow a few times each year. Also, as I said before, we need to keep the HVAC units in the attic.

Please help! I feel like I'm going in circles. Thank you!!

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alphonse

I'm surprised no one answered your question.
There are two issues here. One, insulating living space,or future living space. Two, addressing proper roof function.
Soffit and ridge venting deal with the second but are complicated by the first. If the rafter bay is to be insulated, asphalt & some other roof materials require temperature control beneath them. The typical strategy is the use of "chutes" below the sheathing in consort with soffit/ridge.
"Or should we have no venting and just spray everything with closed cell foam (or other foam spray)?"
No venting, with any insulation sounds like trouble as regards issue number two. The advantage of the spray ins is inherent vapor barrier. Look into a new roof on sleepers with that plan. That would enable full depth insulation AND roof venting.

    Bookmark   June 6, 2009 at 5:46AM
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