Do knee walls in an attic need blocking between studs at the top for drywall?

Question

I'm finishing our attic and I can't quite figure out the best approach. The house came with the attic already "framed" with a knee wall, but the studs are just just angled directly into the rafters like this.

As you can see, there's no top plate of any kind. My understanding is that you need a continuous surface to attach the drywall, so I need a top plate for the knee wall and a bottom plate for the ceiling wall. Or is that overdoing it? If so, what prevents the drywall from cracking at that seam?

We've already done one room by cutting a short top and bottom and toenailing them in between the knee wall studs. As you might imagine, this is very time-consuming and frankly doesn't look great. I don't want to rip them out a build a whole new wall because I'm not 100% confident that none of them are structural. I've considered just building a new frame on top of the existing studs with a whole new top and bottom, but that also seems like overkill (and complicates insulation).

I tried researching this elsewhere, but all the discussion I found centered whether to bevel the top plate when you build it new. I never found any discussion one way or the other on a bottom plate for the ceiling wall. Do you generally not attach the bottom edge of the drywall to anything?

So what's the best way to approach preparing this wall for drywall?

Answer 1

The normal way to do this is to install blocking between the rafters (for the ceiling drywall backer) and between the studs (for the wall backer). You don't need to toenail all of them... you can screw about half of them.

Easier from a building perspective, run full length 2x4s (or equivalent) top, middle and bottom of the wall (assuming it's under 4' -- if it's taller, then 2 middles). Run 2x4s on the underside of the rafters on 16" centers. You've probably figured out by now that this is a ton of lumber with the added non-benefit of less habitable space.

Neither of these options require beveling. A tiny gap at the edge of the drywall doesn't matter.

If the underlying problem is the cutting, rent a miter saw for half a day and cut your blocking in one swoop.

Answer 2

My apologies here, and I don't mean to go against the grain here. Don't concern yourself with adding block to act as a retro top plate, it is total overkill.

The way I see it, if you block those ends of the drywall just because of a change in the plane, does that mean that blocks need to added at a corner where a wall meets a ceiling, or where one sheet butts another in any occurrence?

If the concern is what the drywall will do in between the vertical studs, gravity will or should be the only factor, then the sheetrock on the wall will support the ceiling. What I would pay attention to is what type and how much insulation you will put in the rafters. Fiberglass needs baffles and air space over the batts. Foam is much more flexible in its install. The reason I mention it is, it does not look like there will be enough room in the rafter depth to add enough fiberglass to have enough R value and have the 2" space needed for ventilation. If you go with spray on foam, that is a different story, what you have should work.

Answer 3

As long as your span is within that specified for the drywall that you are hanging, blocking is not needed - no more so than it is on a wall or ceiling, where the seams butt together perpendicular to the studs/rafters.

Most typically what is done is you hang the first sheet right up into the corner, then over-bevel the second, so it overlaps the first. You could also bevel both sheets, but the important thing is that the second sheet is firmly resting on the framing, more so than trying to get a perfect, tight seam.

When taping, it is also easiest to let one side dry before coating the other, to get an even seam.

Answer 4

While this is an older thread, it is in the first page for some search results, so let me add some additional information for others with similar questions.

You can attach drywall to these walls as shown without additional block BUT you shouldn't for 2 reasons.

One - fire blocking. This assembly lacks adequate fire-blocking as required by building codes.

Two - air barrier. To meet energy codes AND have fiberglass insulation work as intended, it needs to have an air barrier on all six sides. It is precisely this type of missing or inadequate air barriers than make bonus rooms like this hot in the summer and cold in the winter. Search for kneewall air barrier and the few extra minutes spent before drywall will make this a much more comfortable space, not to mention lest costly to heat and cool.

Answer 5

If it were me I'd notch out the top of each one to fit a 2x4. Make a number of cuts with a saws-all or skill saw then break it with a hammer. Finish up with a chisel.