LESLIE: Lloyd in Washington is on the line and needs some help insulating a cathedral ceiling. What is going on at your money pit?
LLOYD: This is going to be a great puzzle for you today.
LLOYD: This is not your normal house. It’s a 12-sided house with a cathedral ceiling.
TOM: Oh, that’s interesting.
LLOYD: And I would have to say that there’s two questions here. One is how to insulate that ceiling and the second is how to ventilate it or put a (inaudible at 0:05:53) in. The roof’s a 10- and 12-pitch with 2×12 rafter bays. And the rafters are spaced 24 inches apart.
TOM: OK. We will only answer this question if you can tell us what a 12-sided shape is called.
LLOYD: A dodecagon.
TOM: Oh, man, you got it.
LESLIE: It’s his house.
TOM: It’s a dodecagon. I admit it, I had to look it up. I was curious.
Alright. Look, this is actually going to be a lot easier than you think. You’re thinking in the traditional sense, alright? You’ve got some tough roof spaces here. You’ve got cathedral spaces, you’ve got a lot of small spaces. You have a depth of a rafter that may be only 6 or 8 or 10 inches deep. You don’t have a lot of room. How are you going to vent this?
My answer is this: forget about venting, forget about traditional insulation. This is a perfect application for spray-foam insulation. Here’s why. First of all, you’re going to get much more insulation ability out of the spray foam. It’s much denser, you get a higher R-value per inch. When you use spray foam, you do not have to ventilate the roof. It doesn’t work that way. It doesn’t require air to go through it to dry it out. So, the spray-foam installers will spray it underside of all of that roof space, trim it flat.
If you want to put a sheathing on, you could do it on top of the spray foam. You’ll never have to worry about ventilation. The nice thing about spray foam is not only does it insulate, it also air-seals so you don’t get drafts. Because if you have all those sides of the house, I imagine you’ve got all that many more places that air can leak in. So, spray foam eliminates that, as well.
So I would definitely recommend spray foam for this house. Now, I used Icynene spray-foam insulation in my house. I was thrilled with how well it came out. So you can talk with them. We wrote a guide to insulation that’s on our website at MoneyPit.com. That might be some help to you but this is a perfect application for spray foam.
LLOYD: To open all that roof up at one time, to me, would seem like it’d be very difficult. Might even be a little bit dicey as far as structure goes, I’m thinking.
TOM: Well, are you talking about opening up from the outside or from the inside?
TOM: Why would you do it that way? I would do it from the inside.
LLOYD: If you’ve seen the house, the walls are over 10 feet high in the main floor and then it goes up to a cathedral ceiling. That’s another …
TOM: Well, what do you have on the underside of the ceiling?
TOM: You have sheetrock. OK. So here’s your choice. You can either tear off your roof, tear off your roof sheathing, spray it, put the whole roof back together. And frankly, if your roof was bad and it was ready for replacement …
LLOYD: It is.
TOM: It is?
TOM: It’s really bad? Alright. Well, maybe that’s the way to go then. But you’re going to have to go through the extra work of tearing off what’s probably perfectly good sheathing and putting it back, you know. Or you could remove the ceiling from inside the house.
The fact that it’s 10 feet, yes, makes it more difficult but drywallers that do this every day work in that height and much higher. You’d be amazed. A trained crew of drywallers can move through a house very efficiently. And I wouldn’t be the least bit surprised if they couldn’t tear all of those ceilings out in just a few hours and put them back in a day or so and then another couple of days for spackle if you have the right company working.
So it’s going to be expensive either way but if you want to get this space insulated, you’ve got to go in from the bottom or the top. There’s just no other way to do this. I wouldn’t even consider blown-in because, again, you have to ventilate it and there’s no way to do that.
LLOYD: Mm-hmm. Right. Because the cupola sits on top of it, which is 9 feet across. What it does, it goes – it’s six-sided. So you go from 12 to 6.
LLOYD: But what you end up with is six trapezoids and six triangles.
TOM: Now, are you a mathematician for your job or something? Do you teach math at a school?
LLOYD: How did you know?
TOM: I could tell, I could tell.
LLOYD: Yeah. Well, I used to teach shop and I was a machinist.
TOM: Oh, yeah? Me too. That’s cool. I used to teach it, too.
LESLIE: You guys have that in common.
TOM: Yeah. Alright. Well, that’s very cool. It sounds like a really neat house and we wish you a lot of luck with it. But look into the spray foam. I think that’s the only way to go. How you get there, you know what you’re up against. But give it a shot, OK, Lloyd?
LLOYD: OK. Sounds good. Thank you.