Insulating finished attic


Old 01-14-04, 06:51 PM
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Insulating finished attic

I have a cape cod (1 and 1/2 story) that has a pretty much unfinished upstairs. We are adding on to the back of it, a two level addition like the current house, and I'm going to go ahead and finish the current attic then, too. Right now there is just a little 60 year old insulation above the first floor ceiling. But when I finish it off, I'll have to insulate just below the roof. My main question is about the angled part of the wall, between the knee wall and ceiling, and how to fit insulation in there. The rafters are only 2 x 6, so I'm wondering if I need to sister wider boards in there in order to have room for adequate insulation for Ohio, plus the baffles I suppose I'll need to ventilate just below the roof deck. And if I do that, could I tack on steel studs, which may be cheaper than lumber?

Any help? Thanks.

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Old 01-15-04, 09:17 AM
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Most building codes and enforcement are practical. In other words, with existing structures if it is impractical to meet insulation code requirements due to the type of structure, code enforcement officials will allow the most practical amount of insulation. If for some reason they do not allow it, then they must provide you with an approved solution. You should contact your local building code enforcement department and inquire about this situation.

As far as your querries about obtaining the insulation requirements. The sistering will work and the way you intend to tack the steel studs will not. This is because the way loads are distributed with rafters, which is known as torsion stress or twisting if you prefer. The sistering will restrict movement and the tacking will allow too much movement. This has nothing to do with structual integrity, it has more to do with cracks in the spackle where you joined the sheet rock. Furthermore, the distance between your rafters will be different from between your metal studs if you tack them to the rafters. This is because the steel studs form a "U" or "C" shape and you will end up with a gap inside the steel stud if you use the same insulation for the steel studs that was used for the rafters.

A way the steel studs can work is by installing them perpendicular to the rafters. Movement is restricted by attaching the studs to the adjacent rafters. In this application you have to install nailers on the ceiling and knee wall. This should be cut at an angle to provide a smooth transition from the steel stud to the nailer. The way to determine the angle is to place a wood 2 x 4 on either the slant ceiling, ceiling or knee wall. Take a level and lay it accross the steel studs to one edge of the 2 x 4. Draw a line under the level on the edge of the 2 x 4 and that is the angle you have to cut the 2 x 4's. Tip; if you cut a 2 x 4, lengthwise in half at that angle, you end up with two nailers the same length. Use the mark on the edge of the 2 x 4 to adjust the angle of your saw blade. It is easier if you have a table saw. Also test place your first cut before you cut the other nailers. And do not assume the angle is same for the ceiling as for the knee wall or one slant ceiling the same as the other. Measure twice, cut once for all the ceiling and knee wall nailers. The level will determine if the nailer should go on the slant wall or ceiling or knee wall. When you test place the nailer, you should make a mark so you can reference where it should go when you finally attach the nailer and use the level to extend the mark along the nailing surface. Also, you can use 2 x 3's in this application if you want. Plus install the studs at a distance that will accept the insulation without having to cut or fill in gaps.
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