LESLIE: Alright, if you’ve got a question about attic insulation you’d be Mark from Ohio. Mark, how can we help you?
MARK: Yeah, I’d like to turn my attic into, basically, a toy room for my son and I.
MARK: And I’m wondering just a couple quick questions. Is that considered – I’ve got a full walk-in staircase that goes upstairs. It’s not one of the pull-down things. It’s a regular staircase.
MARK: Is that considered a living space that I have to have egress windows in and such?
TOM: Are you using it as a living space right now, Mark?
TOM: Well …
MARK: No, it’s just an attic and I just want to turn it into a toy room so I can put my trains and his slot cars up there.
TOM: Your trains and your slot cars, huh?
MARK: And so that ties in with the insulation that I want to ask about but that was just one question that came to mind right quick.
TOM: Alright. Well, first of all, it’s not considered an egress in the sense that you have to have an additional exit from it as far as I know but you need to check with your local code authorities to be sure.
Secondly, what your real question is, if you turn that into a heated space …
TOM: … what do you about the insulation.
TOM: And the answer to that is if that attic is going to be a heated, finished space, then the insulation moves from the ceiling of the second floor up to the underside of the roof rafters. That becomes the thermal barrier.
Now, to do that you have to be very careful to make sure you maintain some ventilation space. You can’t just insulate the entire rafter bay because you’ll trap moisture against the underside of the roof sheathing and cause it rot out. So what I want you to do is this. If your rafters are 2x8s you put in six inches of insulation. You leave about a two-inch gap between the insulation and the underside of the roof sheathing so that you have some airspace there and then make sure you put ridge vents in and soffit vents in – soffit vents at the overhang and ridge vents at the peak – so that air sort of washes under that space and pulls out any moisture that collects there.
Many times I’ve seen folks try to overfill that space of the rafter bay with insulation and after about five to eight years you start to see sagging of the roof sheathing from the outside as the wood above that insulation rots away. So it’s important to get that airspace in there.
MARK: Alrighty. If I were to – that’s not a problem. I’ve got a ridge vent and perforated eaves. What about the floor of the attic? Can I put some insulation in that just so that if I kept the upstairs, say, 50 degrees if we’re not playing to keep the rest of the house warmer?
TOM: And think how much quieter it’ll be with you up there playing with those slot cars here. (Leslie chuckles)
TOM: Your family below will not be disturbed so there is some science to this. Yeah, I think it is probably a good idea, in this situation, to keep the insulation where it is and just add the additional insulation underneath the roof rafters.
MARK: Alrighty. Do I need a vapor barrier between the second floor and the attic?
MARK: If that’s going to be, you know, say a 20-degree difference between the living space and the upstairs that’s not being used.
TOM: No. No, I don’t think so. Not in that case.
MARK: OK. Just in the ceiling and the attic roof.
TOM: Yep. Mm-hmm. That’s right.
MARK: Alrighty. Thank you much.
TOM: Alright, Mark. Thanks so much for calling us at 888-MONEY-PIT. As Mark zooms off (Leslie chuckles) to the slot car racetrack in his attic.
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