Ventilate a Cathedral Ceiling
LESLIE: Jennifer in Alaska is dealing with some moisture issues in her house. What can we do for you?
JENNIFER: Yeah, actually, I have question regarding our – I guess our roof and our ceiling. We have a low-pitch roof with cathedral ceilings. The roof doesn’t leak but our ceiling drips on us.
TOM: You have a low-pitched roof with cathedral ceilings. The roof is not leaking but your ceiling is dripping. What’s dripping? Is it condensation?
JENNIFER: I think it’s condensation from 30 years worth of moisture saturating the insulation.
TOM: Hmm. That’s not good. You know, cathedral ceilings have to be very carefully ventilated and, typically, the way you vent them is this: let’s say that the roof rafter is a 2×10; you would put in like six inches worth of insulation and leave four inches between the insulation and the underside of the roof sheathing. If you are so saturated that you’re getting that level of condensation, it is almost a given that you probably have some decay inside that roof cavity and eventually you’re going to end up having to open it up to fix all that. In fact, the roof sheathing may very well be delaminated by this time.
JENNIFER: Yeah. We were just wondering the best way to fix it, I guess.
TOM: Well, the best way to fix it is to take the roof apart from the outside. How many layers of shingles do you have on there?
JENNIFER: It’s not shingles; it’s torch down.
TOM: Oh, it’s torch down. Well, oh, man.
JENNIFER: Alright. Do we have to add an attic or is there a way to fix it without actually putting trusses and an attic?
TOM: (overlapping voices) Well, if you took the ceiling down from the inside – how thick do you think your roof rafters are?
JENNIFER: Think they’re 2×12 or 16; I’m not sure.
TOM: Yeah? Because what you should have is you should have ventilation at the soffit area at the overhang. And if you don’t have a soffit, you can create it with something called a drip-edge vent. Then you should have more ventilation at the top edge.
You want air to move into the roof cavity, up underneath the roof sheathing and then exit at the ridge area, so to speak. So that’s what you want to try to create. You need more ventilation and probably less insulation and that will stop the condensation from forming.
JENNIFER: OK. Alrighty. Thank you.
TOM: You’re welcome. Good luck with that project. Thanks so much for calling us at 1-888-MONEY-PIT.
That is a bad, bad ventilation problem right there, when it’s so bad that it’s condensing inside the house. And mold issue, too.
LESLIE: Yeah. And not good for, you know, indoor air quality and health issues.