How to Properly Insulate and Ventilate an Attic
LESLIE: Mike in North Carolina is doing some work up in the attic. Tell us what’s going on up there.
MIKE: Hi, guys. Well, I’m a first-time homeowner and I have a two-story house with a relatively large attic. And in the summertimes in North Carolina, it gets very hot and humid in the summertime. So I’m looking to install insulation in my attic to cut down on the energy bills.
MIKE: But I’ve been looking specifically at the foam-insulation option, to also close off the attic to reduce the humidity, improve the air quality and reduce insects and bugs and things.
MIKE: The main issue I have, though, is that in my attic, I have an air-conditioning unit and a natural-gas heater. And the foam company is asking – is basically instructing me to install an air intake, which basically pulls air from the roof, from the exterior of the house, as compared to pulling it in from the closed – what will be the closed interior of the attic.
However, the contractors that I’ve spoken with seem to be hesitant about doing that and are trying to sell me on a high-efficiency, 90-plus-percent efficiency type of heater that is intended to be made for crawlspaces or enclosed spaces. And I’m getting some sort of conflicting information about whether retrofitting the current unit is a good idea or will I indeed need to replace that natural-gas heater in order to move forward with the closed attic.
TOM: Alright. Well, first of all, you’re going to insulate the floor of the attic between the attic and the unfinished attic space and the finished living space below. Is that correct?
MIKE: That has some existing traditional insulation but no, what they’re intending on doing is spraying the expanding foam insulation on all of the roof and the side walls and closing off the …
TOM: Why are you – is this attic ever going to be finished?
MIKE: No, it is not.
TOM: So why are you doing that? Why are you further insulating an unfinished space? That’s not how you insulate a house. You insulate between the heated and the unheated or the finished and the unfinished space. So if you’re dissatisfied with the amount of insulation, you can add to that insulation. But I don’t know why you’re going to insulate the underside of the roof and the side walls, because that’s not a finished space. That’s not – I don’t see how that’s really going to help you that much.
How much insulation do you have right now in that floor structure?
MIKE: It’s approximately a foot of that kind of white, shredded material. I don’t know exactly what it’s called.
TOM: Cellulose? It’s not – or fiberglass?
MIKE: It’s fiberglass.
TOM: OK. So it’s – and you say it’s shredded. Is it batts or is it loose, like blown-in fiberglass?
MIKE: It’s loose.
TOM: It’s loose, yeah. Well, look, most homes need about 18 to 22 inches of insulation, so you have about half of what you should have on that floor.
I would rather – much rather – I know you’ve been investigating foam but I would much rather see you double-up the fiberglass insulation on this attic floor. You’re not going to be able to use that space for storage anymore after that, because the insulation is going to be too thick, but it doesn’t sound like you want to do that anyway. And then what you do is you reserve a space near the furnace so that you can get up there to service it. And that’s going to be a heck of a lot cheaper and I think it’s going to make a difference.
Yeah, I wouldn’t worry too much about the fact that the attic gets really hot; it’s supposed to get hot. The attic is supposed to be the same temperature as the outside, if it’s properly ventilated. And that’s another thing to look at, by the way. Most attics are under-ventilated. If you don’t have enough vents, that’s another reason it gets so hot up there. So you could make sure you have a full ridge vent going down the peak of the roof and complete, open soffit vents going down the overhangs and make sure you have plenty of air in there that way. And that’s going to help.
But I would much rather see you double-up on the floor insulation right now than enclose the whole attic, because I just don’t see that that’s going to buy you that much. It’s the most expensive way to go and it leads to a whole host of other complications, such as what you usually call to ask about, which is: how do you get combustion air to a furnace when you’re sealing the attic?
MIKE: Right. That is correct. I guess I was under the assumption that my second-floor air-conditioning unit was not able to keep up during the hot summer months due to the extreme heat in the attic. And that was my original intention of wanting the sort of extreme foam, closed-attic situation.
TOM: You’re not going to cool the attic, OK? It’s still going to be hot up there, even with the foam. And yeah, it is a little less efficient because it’s warm up there, potentially, but I would improve the ventilation to deal with that. Having more passive ventilation is the way to go. But if you double-up the insulation on the floor – because it sounds like that’s what you really desperately need is a lot more floor insulation – that will make sure it keeps the cold side cold and the hot side hot.
MIKE: OK, great.
TOM: Alright. There you go. I think …
MIKE: You may have just saved me a lot of money.
TOM: I think we did. So our work is done. We can quit for the day.
LESLIE: Thanks so much.
MIKE: Well, I really appreciate your answers, guys.
TOM: Good luck with that project, Mike. Thanks so much for calling us at 888-MONEY-PIT.