Leaking ceiling when weather shifts from cold to warm
I have a small addition attached to my house, 10 x 15, with the ceiling height to the ridge of 12 ft.
It is approx. a 6 pitch with a Cobra raised ridge vent. It has ice and water and 30-lb. felt with 50 yr Owens Corning architectural shingles that were installed 3 yrs ago.
The roof seems to be alright and I believe the problem is inside (moisture leak due to humidity).
No leaks through hurricane Sandy or rainstorms throughout the summer. Only leaks when it goes from extreme cold to mid 40s and low 50s.
The interior of the room is knotty pine slats 1×6 and they follow the pitch of the roof. there seems to be a 7 inch gap with poor insulation behind the pine board and the roof deck.
Sorry so long — but here’s the question: How would I attack this dripping issue? Its already vented and i can’t take down the pine ceiling. If i have to take the small portion of the roof off then so be it – but what product would i use and do I insulate and close it or leave it vented?
Also, is there an underlayment to go over the roof deck (besides 30-lb felt) that will stop the plywood from frosting on the inside? Assuming felt and shingles to go back over top of it.
Thanks,
Tim Smith
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Replies
Tim,
Your roof is not leaking. The water is condensation that accumulates on the underside of your roof sheathing as ice. When the weather warms, the ice melts and drips back through your ceiling.
The origin of the moisture is the interior air, which is humid. The reason that the air is able to reach your roof sheathing is that the builder of this room forgot to include an air barrier at the ceiling level. The 1x6 pine boards are not airtight -- not by a long shot -- so the warm air from your house is racing through the gaps in your ceiling. This not only leads to condensation and drips -- it also wastes a tremendous amount of energy.
If you want to address the problem from above, you will have to remove the roofing and the roof sheathing. Once the rafter bays are exposed, you can remove whatever insulation is in there now (probably fiberglass batts). Then you can install spray polyurethane foam insulation from above, directly against the top of the ceiling boards. You may need to install cardboard rectangles first, to limit the amount of spray foam that squeezes through cracks between the boards.
If you don't want to use spray foam, you can install a thick layer of rigid foam (or, better yet, two layers of rigid foam installed with staggered seams) on top of your existing roof sheathing (after stripping the shingles first, of course). Then you can install a second layer of plywood or OSB on top of the rigid foam, followed by new shingles. If you go this route, you need to do a careful job of air sealing the ventilation chutes, both at the soffits and at the ridge. This will require some spray foam.
For more information on this topic, see How to Build an Insulated Cathedral Ceiling.
Thank you Martin - I appreciate your quick response. and am liking option B using the rigid foam over top of decking. When you say rigid foam I asume you mean the pink foam board that carries an R factor - using 2 layers how thick should the foam board be? and should I do away with the cobra raised ridge vent closing the ridge in or continue to let it breathe?
Tim,
There are three main types of rigid foam: EPS, XPS, and polyisocyanurate. Any one of these products can be used to insulate a roof. The pink foam you mention is probably Owens Corning Foamular, which is a brand of XPS.
For more information on rigid foam, see Rigid Foam Insulation.
You didn't mention your location. But if you are near the area affected by hurricane Sandy, you are probably in climate zone 4 or 5. In your climate zone, the building code requires a minimum ceiling R-value of R-38.
That means you need at least 10 inches of EPS, 8 inches of XPS, or 6 inches of polyiso. Because it has a higher R-value per inch, polyiso will be the easiest to install (you won't need such long screws).
You could install 2 layers of 3-inch-thick polyiso.
If you install rigid foam on top of your roof, you don't want open vent channels. Remove the Cobra vent and throw it away. Use a 2-component spray foam kit to seal the top of each vent channel at the ridge. Then install new cap shingles.
At the soffit, you'll have to remove the soffit and expose the bottom of the ventilation channels. Carefully seal each ventilation channel opening with spray foam.