How To Determine the R-value of a Home
LESLIE: Gary in Nebraska’s beefing up insulation in the house and you’ve got a question about R-value. What can we do for you?
GARY: Yes, we were trying to determine what the R-value of an existing wall was and wondered if we could stack layers of styrofoam floor to ceiling and measure the outside temperature, the temperature of the wall and the room temperature and determine the R-value of the wall by that.
TOM: Well, if you tell me the wall construction, you can figure out what the R-value of the wall is. What’s the – what’s the wall physically made out of?
GARY: Well, it’s a wood siding and sheetrock, but without knowing what – how much insulation is in between, (INAUDIBLE) …
TOM: (overlapping voices) Well, you can determine that. What you want to do is you want to take the outlet covers off – the electrical outlets – get a strong flashlight and you can usually poke around the area where the drywall’s cut around the electrical outlet box and determine whether the – whether or not there is insulation in there. Now, assuming it’s a standard four inch wall – 2×4 wall – and you have three – four inches of insulation in there, what you have is an R-13 insulating area. And then the wood doesn’t really add much to it so you can figure the whole thing’s probably got an R-13 or R-14; not very much.
But if you’re trying to determine where you need to add insulation to your house, the priorities should be, Gary, to start in the attic. The ceiling is the first place you want to insulate. That’s where you have most of your heat loss. So you do the attic first. Then you do the walls and then you do the floors; in that order, kind of working your way down. If it turns out that the walls don’t have insulation in it, then you could also add insulation with a blown-in system. But one way or the other, you can get them warmed up.
Gary, thanks so much for calling us at 888-MONEY-PIT.