Excess humidity in spray foamed attic
With a new home being built, we invested -no- overspent for spray foam insulation instead of using fiberglass bats. The basement came out fantastic, the walls for the first and second floors okay, and the attic has been a bit of a disaster. I’ll go into the details on another post why I think sprayfoam is overhyped and a poor economic choice for insulating a house.
Running into high humidity in attic – tiny icicles on roofing nails that have penetrated roof sheathing. Have a ridiculously loud 12″ CFM fan that will turn on at 80% RH. That loud fan is keeping my 2 year old and 8 month old awake at night (it is right over their bedrooms. Humidity monitor in attic ranging from 78% to 85% from evening to morning.
1) Foam is Demilec Open Cell Agribalance Foam Sprayed 6 Inches and shaved in walls / 8 Inches in attic. Perm rating for thickness approx 1.2 Perms.
2) Foam was applied in 20-30 degree environment
3) Live in Upstate NY – class 5A (GBA Map)
4) Class 2 vapor retarder requirement for attic request was ignored – contractor sprayed to sheetrock in attic.
5) Rheem sealed modular gas furnace exhausting from basement wall
6) Panasonic DC Fans on in upstairs / downstairs continuous at 40 CFM
7) Outside make up air with Aprilaire 8126 to furnace on 1 hour cycle
8) Hip roof design
9) Maintain 30% RH on first floor and 34% RH on second with furnace recirculating humidifier
I missed providing a spec for the builder a raised hell truss for the attic, which probably lead to the issues I am having now.
So for the attic, the spray contractor sprayed 8″ of open cell 0.8 lb foam. There are numerous defects in the foam (crusting, cracking) due to cold temperatures and a crew that looked like they had all 3 weeks of training. They never bothered spraying the top plate on outside walls, and the thin foam attic baffles they installed butted up against the outside soffit wall, resulting in limited ventilation.
So had the contractor come back and spray the top plate and put the rafter baffles in the proper spot (base 1 foot away the soffit wall). Well they did this correctly, actually too good. Since there was foam on the already on the attic floor, the foam on the plate expanded up and crushed almost every rafter vent and effectively created a sealed attic.
Now go figure – I have a humidity problem in the attic. Now obviously the rafter baffles need to be fixed. I plan on having the foam cut out (and then having to dispose of this junk) and then using the following:
1″ extruded foam board cut in 2″ wide strips and tacked to side of rafters, and then press fit 16″ wide 48″ extruded foam board to create a heavy duty rafter baffle. The 2″ strips will create a 2″ channel.
Is this the best way to do this? I can not find any heavy duty baffles that can be retrofitted, and the insulation will help as I don’t have much space at the end due to the non-raised truss.
The other question I have is around proper installation initially, the use of vapor retarder. I would think a class 2 would be a good idea underneath the attic insulation, but even a class 1 is OK, since the attic is ventilated. Would a class 1 pose a problem with a roof leak not being able to be identified until it was way too late?
I am concerned that with a 35% RH and a cold day outside the attic RH is shooting up to 85% at 21F. I would have thought that a 2 perm open cell assembly with drywall, latex paint would be more resistive. Also the area above the master shower seems to have more moisture on the attic roof deck, it looks like a mini ice waterfall on the interior of the plywood. My belief is that the Panasonic fan was half dug out to make sure it wasn’t encapsulated in the foam and there may be some leakage going on here. Also because the fan is exhausting out of a discharge from the soffit, and that there is significant recirculation of the humid air back into the attic (one of the few areas that does not have crushed baffles.
I am planning on adding 10″ of additional cellulose once I get this situation fixed.
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