A little while ago, we illustrated how to insulate an attic knee wall to create living space. It’s a bit of a complicated process, so this time we will show you how to do it the easy way: cathedralizing the insulation, which means putting it all up in the roof.
Of course, if you are remodeling, you’ll need to scoop the insulation out of the way to place the subfloor and knee walls, but we’re going to keep it simple and pretend it is new construction.
And just like with new construction, the framer always throws a wrench in your plans.
Even though you asked them to leave the knee walls out, they went ahead and framed them because they didn’t want to come back to the job. So we’re going to have to insulate the roof with the knee walls in place.
Full-length ventilation baffles for vented roofs
First thing it to add full-length ventilation baffles if you are venting the roof.
Next is to insulate the roof cavities. Because it is sometimes hard to hit the right R-values with insulation between the rafters, you may need to add some rigid foam insulation to beef up the thermal resistance.
And because we know that insulation is much less effective with wind whistling through it, you will have to seal the edges, where it meets the framing.
Air seal the insulation edges
Do that in every framing cavity along the bottom and top.
Of course, you simplify the process even more by using spray foam in the roof assembly, which air seals and insulates in one step.
There you have it—the simple way to create living space out of attic space.
