Housed Versus Butted Stair Stringers
If I understand you correctly, the staircase is between walls with the stringers already cut out and nailed in place by the framers. The outside stringers are spaced off of the framed wall 1-1/2" by using a 2 x 4 nailed flush with the bottom edge of stringers. This is framed for a build-in-place staircase, which means butt joints. In this instance, I would not attach the skirt directly to the treads. There is too much of a chance for squeaks since the stringers will move as you walk up them but the wall won't.
This is how we install them. Assuming drywall has already been installed, cut and attach skirt boards directly to wall, not to stringers. There is enough room for drywall and your skirt board to fit between the stringer and wall. Next, cut and install risers. Don't attach them to skirts, only the stringers. If stairs will carpet, leave approx. 1/8" space at each end. If they will be visible, back cut your risers slightly and install within 1/32" of skirts, but not touching them to prevent squeaks. Finally, cut and install your treads. Again, don't contact the stringers or you will have squeaks. As each tread is installed, reach behind the next riser and fasten it to the back edge of your tread. Use shims to level as necessary and plenty of construction adhesive at any wood to wood contact points.
This is the simplified version. I left out all the parts about cussing the framers for uneven and out of square stringers. Of course there is more detail to it than this, but this should get you started.
From contributor B:
Contributor A is right on including shims and construction adhesive (not glue). Additionally, you will probably find yourself scribing some of the parts. I use a belt sander - a coarse grit is good for the fine tuning. You can also rabbet the riser into the bottom for the tread above it if there is no moulding.
From the original questioner:
The staircases are not between walls, but have an open side. I donít know how this changes things because the open end of the riser must be mitered to meet the skirt (or in this case, we are using tread brackets). The house currently has no sheetrock and is all open, so I have options. The main reason for asking this is because of a staircase I saw on a jobsite. The building had been sheetrocked and the typical construction stairs were in place (between walls, closed staircase).The next time I was there, a finished staircase had been built over the existing stringers. It had a housed skirt (3/4 poplar) on both sides. I was curious how it was built because there was no access underneath and there was no gap between the sheetrock and the skirt. If you know how this was done, could you provide a brief explanation? I was hoping to achieve the look of let in staircase with no gap to the skirts. I will scrap the idea of attaching the treads to the skirts on a site-built stairway.
From contributor A:
You have two different scenarios here. As far as the open side staircase goes, if you want to use let in treads and risers here it will be much easier as you only have one side to let in. Of course you still have the problem of getting to the underside of stairs for driving in wedges. But if it was me, I would still use the above described method only miter the open riser to the skirt.
Now for the enclosed staircase - you have two options that I know of, maybe someone else knows of others:
1) Build a pre-fab staircase using let in treads, wedges, and glue as normal. Just before installing in place, use a circular saw and cut all the rise/run triangles off the stringers so they won't interfere with your finished staircase. Slide into place and secure.
2) Build new staircase, just like pre-fab, but build in place one tread and riser at a time. How? Build it parallel with, or out in front of, the framed stringers. This way you have access to bottom side of staircase. Maybe not a lot of room, but at least there is access. Use temporary supports to hold up the top end of your stringers while you assemble parts. After assembled, remove temporary supports, slide into place and secure. It would probably be a good idea to cut the triangles off in this instance also.
In this scenario, ideally you would build it before sheetrock. Temporarily attach one skirt to wall studs. Cut treads and risers to length, allowing for thickness of sheetrock plus 1/8" minimum on each side as well as thickness of other skirt. This way there is additional room on one side to get all pieces in place. When you install it in place, use blocking behind the skirts on each side to center the staircase in the opening.
From contributor C:
I think the reason for the different answers from everyone is the difference in regional methods of building stairs. I'm from the Philadelphia area and your question is easy for me because that is the method we use in this area. The rough stair is built by the framer
installing temporary treads. The house is drywalled, taped and painted. We come out with all the stair parts mostly pre cut. Lay out the open skirt to the stringer and cut it out. The skirt is tacked on, and then the treads and risers are installed. Glue and Nail your way up the stair. Here comes the tricky part - the skirt on the wall side is top skirted to the treads and risers. This means it is scribed to the top side of the stair. There are a few methods to do this and even a tool you can buy to do this. I came up with a cool design for a tool I think works pretty well. Once cut out, it is nailed or screwed into place. If done correctly you can't tell whether or not it is a pre-fab stair.
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