I prefer to build stairs using housed stringers, which means that the ends of the treads and risers are wedged and glued into mortises routed into the stringers. While this approach sounds like a lot of work, it doesn't take much longer than crafting a decent set of notched-stringer stairs. What you get for the extra effort is a stronger stair, since you haven't notched away half the stringer, and one that's practically seamless.
While I first used this technique to build interior stairs, I particularly like it for exterior ones. The tight, glued joints at the stringer tend to keep out water, and I pitch the stairs about 1/8 inch per foot of run to prevent water from puddling. Stairs built this way stand up to the weather without the cupping and cracking common to most...
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