I’ve recently purchased a 1980 vacation cottage near a lake, 1200 sq. ft. main floor, finished basement, propane and whole house A/C with ducts between floors. 6×12″ beams, 8′ apart, with support through to the basement floor every 12′. The ceiling throughout is T-111 siding throughout. Above that are 2×8″ rafters. Between the rafters is a product I haven’t seen before: 1″ of what seems to be cellulose board, bonded to 1″ of what seems to be isocyanurate foam, glued to 6″ of fiberglass, with kraft paper on top of that. As best as I can tell, this came as a complete system. Above that is sheathing. There is no vapor barrier between the ceiling and the insulation. I don’t know what the original roofing was, but it leaked, and there are stains on the T-111 in places, and it’s clear that at some point water ran down the T-111 in places and ran out at the low point in the roof. The owners had roll roofing installed–perhaps over whatever was on the roof already–I don’t know. (The slope of the roof is barely 2 in 12.)
When I bought the house, I was bothered by a sort of wet wood smell, but the home inspector doesn’t think it’s rot. I removed the 29 year old carpets and pads, which helped, and ventilation and air conditioning have helped some. I think that the house sat uncompleted for a winter with the floor deck on it, as it’s clear that water has run down between the joints in the plywood flooring and down the joists. But no real rotting. A few sheets of plywood are black underneath. The inspector said I should spray on a 2% solution of bleach and water to kill any mold, then paint the underside of the plywood and the joists with a paint with mildewcide in it (should I?).
I removed a sheet of the T-111 ceiling in the bedroom where the smell is the worst. Apart from some rusty nails and some rot on the edges of the T-111 in the worst spot where the water ran out, I didn’t see any rot. But the insulation seemed damp. When I reached up into the fiberglass, it was very humid. The sheathing above it seemed solid. Remember, there is NO ventilation in this roof, and the fiberglass and kraft paper are against the sheathing. After a few days, the exposed insulation seemed nice and dry. And the smell is decreasing.
What should I do? How do I dry out the humidity in the insulation? I had thought that perhaps I should cut slots or holes in the sheathing and kraft paper to allow for ventilation, then install a cold roof above it by nailing 2x2s to the rafters through the sheathing, nailing on new sheathing, then an inch of foam, followed by EPDM roofing. This would let moisture escape, but I’ve read that this could cause a problem by letting it condense on the bottom of the cold roof. Plus, it’s pretty expensive. I’ve read recently that warm roofs are the new requirement for cathedral ceilings (the ceilings in this simple house run from 7′ to 10′). But they also require carefully maintained vapor barriers, and that’s not easy for me to achieve with unpainted T-111 and a ceiling with structural beams.
Please help! I would just as soon do this right, rather than adding to the problem.
Replies
I don't have an answer, but since you haven't had a response, I thought I'd respond to keep your post up so others can see it and respond.
The inspector said I should spray on a 2% solution of bleach and water to kill any mold, then paint the underside of the plywood and the joists with a paint with mildewcide in it (should I?).
Bleach will not kill the mold. It does "bleach" the color from it though, which is misleading to thinking the mold is dead.
There are biocides with Borates (? name brand Boracare ?) that will be a better choice to kill the mold.
You might have two moisture problems. One that the roof had leaked and is now (possibly) fixed by the roll roofing. Two, moisture from the rooms getting up into the ceiling cavity. Moisture is driven up by hot air rising and leaking into the roof via small cracks and gaps.
Personally, I would pull down all the T-111 ceiling. And also all the damp fiberglass insulation. That musty smell never really goes away.
Let everything air out and breathe. Figure out if the roof leaks anymore - garden hose sprayed on the roof, start from the low side and work your way up. Second person is on the inside looking for leaks. Go slowly. Some leaks take a while to show up.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Fill in your user profile, or at least let us know your location and climate, and particularly whether there is much snow there in winter. Answers are tuned to your specific situation.
Given the low slope and not terribly well insulated roof, plus the lack of vapor retarder at the ceiling, your approach for a heating climate should address all three problems. But I wonder if the use of a very low slope in a house built as recently as 1980 indicates a warmer climate with no particular concern for snow and the potential for ice dam problems.
Insufficient insulation will result in melting of any snow on the roof, which can then refreeze at the eves, and the resulting ice dam can back up a long way on a low slope roof. Your thought about using an EPDM roof would address that part. The other thing you could do, which might not be much more effort than just adding a second roof flat on the existing one, is to build this second roof with real rafters and a decent slope to it, with ridge and soffit vents. Then you could tear out the old insulation and ceiling, replacing with something decent.
But tell us more about location, climate, and what limits you are imposing on extent/cost of repairs.
On th
Thanks for your responses. The house is in Eastern Pennsylvania, near Reading. So the climate is hot and humid in the summer and moderately cold in the winter. It's rare to have more than a foot of snow on the roof, and usually there is none in the winter, but I've seen three feet with six foot drifts on a couple occasions over the past 23 years. This will be my year-round residence, though it was used by the previous owners for weekend visits. Is the thinking that if I installed an EPDM roof, removed the T-111 ceiling and the current insulation, and had closed cell foam blown in, I should be okay? Should I put on a PVC vapor barrier between the drywall and the foam? Vapor retardant paint?Thanks again.
Assuming your "EPDM roof" is as described in post #1 (2x on present roof, then sheathing, then EPDM), then you should be ok, I would think. The EPDM is a vapor barrier, but the 2x under the membrane and 2nd sheathing will give you a space for the original roof assembly to breathe. I would be inclined to remove the present roll roofing (if that is the present covering) before laying down tar paper and the 2x spacers. Make sure to provide insect screening where the spaces between roof sheathing layers vent to the air, so you won't have bugs galore in the new cavity.Underneath the old roof surface, remove the old insulation and foam under the deck, then put on sheetrock for ceiling surface. If you use closed cell foam, that's your vapor retarder. If you use open cell foam, you won't get as much R value, and you'd either have to use a vapor retarder membrane such as Certainteed's MemBrain between it and the sheetrock or just use vapor-retarder primer paint on the sheetrock. That will limit diffusion of water vapor through the assembly during the winter. The wood will comfortably absorb what little moisture diffuses in through a 1 perm vapor retarder.Don't use polyethylene above the ceiling sheetrock; that's a vapor barrier (< 0.1 perm). At times during the year, such as summer, you need the ceiling/roof assembly to be able to dry to the interior of the house, to release moisture absorbed by the framing at other times.I'm thinking that others may suggest just replacing the roll roofing with EPDM, and using closed cell foam under the deck, with no 2x and new sheathing. That may work, as long as there are no gaps in the foam (this goes for the other case,too) or gaps in the joints with walls or holes for can lights, etc. that would allow convective flow of moist inside air to carry moisture directly to the cold sheathing layer. Avoidance of poly above the sheetrock, in favor of just a 1 perm vapor retarder, is a must for that assembly, since the ONLY escape for any moisture in the wood above the sheetrock will be by drying back into the house.Have you eliminated the idea of framing a new conventional, vented roof over the old one, and changing the old roof to a conventional attic floor with loose insulation?Edit: looking back at your post #1, you describe the new EPDM roof layer as having foam above the new sheathing. I have to ask what that foam is for, if you have a vented space under the new sheathing, provided by the 2x nailed through to the present framing. The new sheathing/EPDM would become just a layer for shedding rain, and the cavity under the present sheathing provides insulation.
Edited 7/29/2009 11:40 am ET by DickRussell
I really appreciate the advice. No, I don't want to rip off the roof and build one with a steeper pitch and a flat roof. As the photos show, that would remove a lot of the house's charm. I did get it at a very good price, though the suggested improvements eat up a lot of that. Thanks again.
A bit confusing, and I'm not really an expert on roofing. Plus I'm biased - I don't like fiberglass, it just seems to either cause problems or lull you into thinking it's working.
It seems your insulation would trap moisture that might leak into the fiberglass. The foam, if foil-faced as poly-iso usually is, would trap water/moisture on the top side, with a semi-vapor barrier on the other side of the fiberglass.
You don't mention where the building is located. If cold climate (based on your mention of cold roof) and you want real insulation where it counts (roof), with cathedral ceiling... I'd consider removing the ceiling, removing the existing insulation, high-density spray foaming the rafters, and reattaching the ceiling. OK, that's big bucks.
But for that, you don't have to worry about moisture in the rafter bays from either side, it'll get you sufficient insulation (5" high-density poly gets you to R-35 then decide how you want to handle the rest of the space). You'll have stopped infiltration with a complete water/vapor barrier that will stay warm enough on the interior to not allow condensation.
You also need to fix the leaking roof first, or water will get to the roof deck and have nowhere to go except rotting out the sheathing and rafters.
I don't understand your cold roof plan. If the 2x2's are to provide ventilation for the roof deck, then that space needs to be open to the exterior, and the foam on top of the second deck appears to serve no purpose, unless you need the foam for the roofing.
You mentioned cutting holes into the existing decking to allow cavities to dry out. How would you seal the holes so that water getting to your vent doesn't drain into the holes?
The roof line has the most pressure for hot air to exit, carrying moist are with it, which can cause the biggest problems. It's pretty much impossible to get a good seal with fiberglass.
just my thoughts,
---mike...