Normally I wouldn’t dedicate a whole post to a little section of subfloor, but the landing turned out to be a bit involved. When I started building the and fitting the stringers I realized that the landing was wonky. It was ¼” too tall and it wasn’t square. To compensate for being too tall, I decided to use half-inch plywood subfloor instead of ¾” OSB. However, ½” is pretty thin for subfloor, so I devised a scheme for fitting sections of ¾” OSB in between the framing members, glued to the underside of the plywood (and to the framing) to add strength and thickness.

Test fitting OSB

Test fitting OSB

If the landing had not been out of square, this would have been pretty straightforward: just cut some rectangles to fit and done deal. However, given the out of squareness, everything was parallelograms. I’ve learned not to measure things any more than I have to. Measuring introduces more inaccuracy than it eliminates. Instead I put the OSB on top of the opening (generally lining up one edge) and drew the shape from below. Then I cut it out along the lines with the circular saw and fit it into place.

It worked fairly well, though I discovered after I had glued and screwed down the plywood (though thankfully not before it had dried) that one piece that fit between the stair stringers would not fit in from below because I sistered 2x4s to the stringers. I had to unscrew the corner of the plywood on top and slide it in (actually I had to do this three times because it kept falling through). Finally, once everything was in place and the glue was setting, I put in about 7,000 screws.

Landing subfloor installed

Landing subfloor installed

In one section the OSB was squeaking when I walked on the landing. I considered that it might go away once the glue set, but rather than take the chance I used a long 2×4 to press the underside of the OSB up against the subfloor and tightened all the screws. I left it that way until the glue set and now it’s all feeling solid and squeak-free. With this done I can work on the second run of stairs up to the second floor.

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