As one deck builder recently told me, installing the bottom newel posts on a set of porch or deck stairs is a real PITA. To meet code, these posts have to be able to withstand 200-lb. lateral loads. And in some areas, the base of the stairs – typically a post/stringer assembly – has to be supported by footings that bear on undisturbed ground that is either 12 inches below grade or below the frostline (whichever is deeper) … in other words, just like any other deck footings. For some inspectors, a simple poured concrete slab landing just won’t cut it (Glenn Mathewson weighs in on the pros and cons of floating vs. fixed landings here).
If your inspector requires stair footings, you can follow the detail shown in Figure 34 in the American Wood Council's DCA6-12 (see illustration). The problem is, this detail requires not only a buried 4x4 post, but also a buried 2x4 cleat to support the stringer. Are you confident that a pressure-treated 4x4 SYP post that is embedded in soil and perhaps concrete too won’t start to rot? And even if you are, what about the 2x4 cleat, which in all likelihood you will have to cut from PT stock that is NOT rated for ground contact?
Simpson Strong-Tie’s Jim Mailey has come up with an alternative detail that raises the base of the post above the level of the ground while still satisfying the IRC’s post load requirements (see illustrations). Jim’s a smart guy who knows a ton about deck construction, and while his detail relies on a lot of SST hardware, it addresses some serious shortcomings in the DCA6 stair post/stringer connection. And as a bonus, the detail can be adapted to use with posts that mount either inside or outside the stringer. You can read more about his approach here. And be sure to scroll down to the ‘Comments’ section, where Mike Guertin and others offer variations on Jim’s basic idea, useful, for example, when stringers must be spaced closely together in order to accommodate the reduced spans of certain types of decking.
If you work in an area where you’re allowed to support the stair stringers with a floating landing pad, you might want to check out Raymond Valois' article, called Attaching Bottom Deck Posts, also found on Gary Katz’s excellent construction website, called This is Carpentry (thisiscarpentry.com). And if you have your own method that you want to share with other PDB readers, send it along (with photos and sketches) to us at firstname.lastname@example.org.