Installing Manufactured Stairs, continued The stairs come from the shop with the finish floor height and centerline marked on the lowest riser (Figure 9). If you have to trim or shim that, do it so that the change is minor in the center walking path. By code, you have 1/4 inch to play with -- more than you'll probably ever need. Coming out of the shop, I've never seen any of the rise or run dimensions on the stairs themselves deviate from dead-on perfect.

Figure 9. The installer uses a piece of landing tread, supplied with the stairs, to check the fit at the top (left). A label on the lowest riser (right) shows the finish floor height and indicates the centerline of the stairs.

At the top, lay a scrap of landing tread on the riser to check the height. The landing tread comes with the stairs and makes the transition from the 1 1/16-inch tread thickness to the 3/4-inch wood flooring thickness; we install it when we install the floor. The stairs are right when the scrap lies flat on the subfloor and fits just right on the riser. Fastening. The stairs are fastened to the wall studs at the side, under the steps if possible (Figure 10). We also pin them to the landing, and to a cleat screwed into the subfloor behind the bottom riser. Drywall screws seem to work fine for all these locations; when we have to place screws in the stringer above the steps, we countersink them, then plug and sand. Never use nails instead of screws -- that's the one thing that is likely to cause squeaking over time.

	Figure 10. A cleat glued and screwed to the deck serves to hold the bottom stringer tight to the floor (upper left). Screws into the cleat through the face of the stringer will be buried behind flooring and molding. Screws into the studs from underneath are also invisible (upper right). Visible fasteners (left) are counter sunk and plugged.

All around the staircase, we use 5/8-inch shims at the fastening points to hold the assembly away from the framing (Figure 11). That lets us slide drywall behind the stairs later. The joint between wall and stairs will eventually end up being covered with a cove or quarter-round molding.

Figure 11. A 5/8-inch gap is left for installing drywall around the stairs (left). Precut shims (right) speed this process.

Support. On the job we're showing, the shop's installer put temporary bracing under each run of stairs at mid-span (Figure 12). If it were one long run, he'd have put in two braces. It's a good idea to shim the supports to create a slight crown, say, 1/4 inch or so; as lumber shrinks, everything tends to settle and sag a little.

Figure 12. Before leaving, the stair installer places temporary braces at mid-span in each run of stairs. It's best to build in a crown of perhaps 1/4 inch to allow for slight settling and framing lumber shrinkage over time.

If my crew were installing, we'd probably frame up the wall right away, just like any other stud wall, with the top plate right up under the stair treads and with a 5/8-inch gap between the framing and the stringer to accommodate drywall. Again, we'd shim slightly to create that crown.

Making the Choice

Depending on your situation, you may have good reasons for wanting to build stairs yourself. If you're a builder who loves being a craftsman, and if stairs are a big source of satisfaction, you might not want to give that up. But the reality of my business is that I have to provide the best quality I can within a limited budget. As a small-volume custom builder in a tight labor market, I have to use my skilled workers as efficiently as possible. I can't afford to keep a finish carpenter on staff just to build stairs. Manufactured stairs give me and my customers the best value available, and I see no reason to go back. Andrew P. DiGiammois a design-builder living in Assonet, Mass.