How to Insulate an Attic Crawlspace
LESLIE: Jerry in Washington is on the line with an insulation question. How can we help you today?
JERRY: I need to find out if I can insulate my attic crawlspace or not.
JERRY: What I have – it’s a house built in 1960 and it’s a very low-pitch roof. The center of the roof has only got about 18 inches of space above the ceiling joist, to the peak of the roof. And right now, it’s got the under-eave vents. And I want to find out, can I blow in insulation, basically covering all those under-eave vents up and then add more vents over the top of the insulation to compensate?
TOM: Well, if you’ve only got 18 inches in the high point of that ceiling – is that what you’re telling me?
TOM: Yeah. Well, you can only – you don’t want to cover the vents. Are the vents at the overhang, at the soffits?
TOM: Yeah. You need both sets of vents: you need vents at the soffit and vent at the ridge. Because what happens is air will enter in at the soffit, Jerry, go up under the roof sheathing and exit at the ridge, so you can’t block it.
TOM: So all you should really do is to get as much insulation into those floor joists as possible without blocking the soffit vents. And then you might want to add a ridge vent down the peak of the roof, which you can easily do from the outside, to provide that exhaust venting.
Unfortunately, when you have a really low-sloped roof like that, it’s very difficult to get as much insulation there as you might want to get.
JERRY: Yeah. That’s what I was afraid of. I was hoping to be able to go all the way to the edge of the side of the house.
TOM: Well, the thing is if you put all that insulation in there, it’s going to be so damp and moist it’s just not going to insulate. You’ve got to have the ventilation to dry it out, to keep it working properly.
JERRY: Well, you answered my question.
JERRY: It wasn’t exactly what I hoped for an answer but …
TOM: Not the answer you wanted but it is the right answer. So, good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.