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Stair Stringers (7)

Stair stringers form the backbone of a set of stairs. By code, stairs need to be at least 36" wide. Although it's usually possible to get away with just using two stringers, we recommend you add a third one down the middle. This extra stringer will ensure your stairs are exceptionally rigid.

If you click on the riser in the diagram above and then read the section on Stairs and Railings, you can learn all about how to size the notches that get cut into the stringers to form the stairs. For this discussion, we'll look at attaching the stairs to the deck. There are three different ways to do this well.

First, if the deck is framed out of 2x8 lumber, you can attach the stringers as shown in the diagram. Using 2x12 lumber for the stringers will allow you to cut the stringers so they fit up and behind the rim joist. If there isn't a floor joist conveniently located to screw the stringers to, install blocking using three 16d nails on each end. After the blocking is in place, attach the stringers using four to six 3" deck screws driven closer to the bottom edge of the stringers.

If your deck is framed out of 2x10 or larger lumber, cutting the stringers to fit under the rim joists won't work. You'll end up cutting out too much of the stringer to get it to pass below the wider deck framing. In this case, one solution is to run 4x4 posts up from the ground on either side of the stairs right where the stairs meet up with the rim joist. You can make the posts even longer and have them also act as the first set of railing posts on the way down the stairs. After the posts are in place, screw a 2x4 board just underneath where the bottom of the stringers will be to create a ledge for the stringers to rest on.

Unfortunately, there are a few "problems" with using 4x4 posts to support the high end of the stairs. First, you probably don't need another set of posts at the top of the stairs. This will be true if you elected to place your first step off the deck one step down - rather than being at the same height as the deck. Second, most people don't like to have any more posts than necessary. And third, if you live in an area where the ground freezes, the connection between the posts and rim joist may fail unless the support posts are set below the frost line.

A better solution when 2x10 and larger lumber is used to frame the deck, is to lag bolt one or two 2x4's to the underside of the deck. These 2x4 cleats should be as 6" longer than the stairs are wide and set flush with the outside face of the rim joist. In effect, the cleats serve to make the rim joist wider. To attach the cleats, use three 3/8" lag bolts with washers. Make sure the lag bolts are long enough to get a thread engagement of 3" - not counting the tapered tip.

Widening the rim joist on the deck makes it possible to use a metal right angle gusset on the inside of the stringers.  Use the tallest gussets that will fit and place one on each of the three stringers. Make sure to pre-drill the holes and use 1-1/2" stainless screws just barely small enough to screw through the gusset holes.

Attaching stringers is often one of the more challenging parts to installing stairs. Using one of the three methods suggested will ensure the stringer will stay put. To get complete details on how to build stairs, please see the Get A Password page.