Can I Insulate on Top of Plywood in the Attic?

LESLIE: Now we’re going to talk to Velma in Minnesota.

Velma, what’s going on? You have an attic question.

VELMA: I was just wondering if it’s alright to put plywood down before you put your insulation in the attic so that if you’re up there working and you happen to step in the wrong place, you won’t go through the ceiling.

TOM: Yeah, that’s a good idea, Velma. All you need to do, though, is sort of make some little plywood panels that you can move around; not big 4×8 sheets but maybe something that’s like 2 feet by 4 feet so you can kind of move a couple of those around while you’re working to put your insulation down. Remember the rule of thumb for working in an attic that doesn’t have a floor: walk on wood. (chuckles)

VELMA: Right.

TOM: Don’t walk on the yellow stuff.

VELMA: But what I was wondering, is it OK to put some permanent plywood up there.

TOM: If you do that, how are you going to insulate underneath the plywood?

VELMA: Well, that’s why I ask you. Apparently, it’s not alright to put the plywood down and then put insulation on top of it. You have to put insulation under it.

TOM: (overlapping voices) Ah, no. No, no, no, no, no. No, no.

VELMA: I see. That was my question.

TOM: No, that’s the wrong order of events here, Velma. You put the insulation down first and let’s say you have 2x8s for your floor joists in the attic. So you can put 8 inches of insulation down then put the plywood over that.

Now in your particular part of the country, you’re going to want a lot more insulation than that. So what you might want to do is sort of map out an area in the center of the attic where you have your storage and then the rest of the area you could put more insulation that could possibly fit under that plywood. Say you might add 12 inches or 15 inches of insulation so that the majority of the attic is well-insulated and you just leave out a little bit of area for storage. Because believe me, you’re going to need all that insulation with the heating bills we’re going to be paying this winter.

VELMA: Right. But could I ask you why it’s not alright to put the plywood down first and then the insulation on top?

TOM: Well, what you could do – first of all, you’re wasting the space underneath the plywood unless you fill that up.

LESLIE: Plus, wouldn’t it hinder how the insulation actually works?

TOM: Yeah, it could because plywood’s not really much of an insulator. What you could do is you could put insulation down in the floor joist first then plywood over it and then you could add another layer of unfaced on top of that. But you know, I would rather see you just sort of map out the area in the center of the attic that you’re going to use for storage and fill up the rest with insulation because that’s the way you’re going to get the most energy efficiency.

VELMA: Oh, OK. Well, you answered my question very well. Thank you very much.

TOM: You’re welcome, Velma. Thanks so much for calling us at 1-888-MONEY-PIT.