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Floor Framing Layout: Cantilevers and Stair openings

Double up key joists to make headers you can hang joists from
June 20, 2023

A little while ago, we looked at basic floor framing on a square building with very little detail. This time, we going to complicate the floor framing a little.

We’ll add two types of cantilever and an opening into the crawlspace so that the homeowners can stash their holiday decorations down there.

One cantilever is parallel to the floor joists and angles back to the building in a bay window configuration. The other cantilever runs perpendicular to the floor joists, and is squared off at the corners. The opening is big enough for a small stairway, which we will cover in a future animation.

Frame a cantilever by extending the floor joists

Let’s begin with the bay window cantilever by stripping back some of the framing to make it clear what is happening. The floor joists basically extend beyond the mudsill to the depth of the cantilever, which is dictated by the depth of the floor joist, their spacing, and the load that the cantilevered floor must carry.

It’s a pretty simple system. Extend the joists, add the rim joist, and then cut a couple of 45-degree wing rims to tie back to the house. And then fill in the blocking.

Frame a cantilever that's perpendicular to the floor joists

The other cantilever is a little more complicated, but we’ll begin by stripping back some of the framing to get to the meat of the matter: A hole in the framing.

Where the joists run past each other over the beam has to be reconfigured a little bit because we want to double up that joist to make it into a header from which we can hang the perpendicular joists.

Similarly, the partial joists at the other end of the cantilever are hung from the last joist. Add blocks between the joists, slap a rim on the outside, and you are ready for sheathing.


Headers define a stair opening in the floor framing

That we didn’t go over this hole in the floor.

If the opening is more than four feet, you need to double up the header and hang it from double-floor joists.

The other end of the opening sits atop the central beam, so there’s not much we need to do there other than step back and admire our work.

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