How do I insulate my attic for a bedroom with 2-by-6 rafters?

Answered by Jeffrey ~ February 19, 2011 ~ No Comments

I am turning my attic into a bedroom, and I am afraid to put the drywall up because I'm not sure if I insulated correctly. I only have 2-by-6 rafters, and they are not evenly spaced. I put vent trays and fiberglass insulation up. My friend nailed 2-by-2s to the bottom of each rafter. Will they support the weight of the drywall? Do I also need to put up a vapor barrier?

Susie ~ St. Joseph, Missouri

Jeffrey Anderson

Hi, Susie. If your attic rafters are 2-by-6-inch framing members, I assume you used an R-19 batt insulation. R-19 is made for 6-inch framing, and if you installed the vent trays properly, there should have been enough air movement in the cavities to prevent condensation on the back of your roof sheathing without nailing extensions to the rafters.

If for some reason you haven't installed the insulation yet or you still have a section to do, you can probably fit R-22 insulation into the space you have available. It sounds to me like you have a total of 7-inches to work with in your rafter area. Insulation shouldn't be compressed or it can lose its R- value, but I think you could fit R-22 insulation 7.5 inches in without too much of a problem. If everything is already R-19, that should be fine, to0, although you may want to supplement the heat in the bedroom on days that are colder than normal. Modern homes usually have R-30 or R-38 attic insulation if there aren't any space limitations.

Batt insulation is available either faced or unfaced. You have the faced insulation if there is a kraft paper on one side. The kraft paper is a vapor barrier and should be on the living area side when the insulation is installed. The vapor barrier isn't necessary, so even if you used unfaced insulation, that shouldn't be an issue.

You mentioned the uneven spacing of the roof rafters. What I normally do is purchase insulation in a width that fits most of the spacing which is normally 24 inches. If I have some rafter spacing that is less than that, I just trim the insulation down to fit. If the insulation is cut a little wider than the space, friction will normally hold the batts in until the sheetrock is installed. Insulation companies have inexpensive fasteners that can be used to hold the insulation in place if you didn't cut it wide enough, and I think they are also available at home improvement stores. You shouldn't have a problem finding any around St. Joseph, but if you do, check some of the larger cities in Missouri.

Hopefully you don't have any spacing wider than 24 inches, but if you do, just cut another piece of insulation to fit in adjacent to the 24 inch piece.

I'm a little concerned about the 2-by-2 extensions that were added and their capability to hold the drywall. You might want to add some long screws to supplement the nails your friend used. To be absolutely sure they will support the weight of the drywall, you may want to have a drywall contractor take a look and see what they think. The last thing you want is for a sheet of drywall to fall on someone. I doubt that would happen as you can usually tell when there's a problem with drywall before anything drastic happens, but it's better to be safe than sorry.

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