Building Deck Stairs (Phase 5)
Building deck stairs (phase 5 of 7), of the 10x10 deck example, is an important phase of deck building. If your deck is more than about 8" (203 mm) off of the ground, you will need stairs for your deck, even if it is only a single step.
Several tutorials on mycarpentry.com, discuss two ways to attach stairs to a deck or landing - either with the top step mounted flush with the level of the deck (flush), or where the top step is attached a full step height below the deck or landing (standard). Either way is acceptable when building deck stairs. The examples in this article use the standard attachment method.
Building Deck Stairs
The first step to building deck stairs is to determine the Total Rise of the stairs. The most common way to do this is to place one end of a level on your deck and extend it over the lower landing or ground where the first step will start. Use a tape measure to determine the distance between the bottom of the level and top of the landing.
In this example, there will be a concrete landing at the base of the stairs. The width and depth of the landing must be a minimum of 36" (915 mm). Our concrete landing is 48" x 48" (1219 mm), because it will also support the base of the stringers and the rail posts, discussed in the Stair Railing tutorial.
The Total Rise from the top of the wooden form to the finished deck height is 40 3/4" (1035 mm). Navigate to the Stair Calculator and enter 40.75 into the Total Rise [A] field. If you accept all of the default input values, the following results will appear.
When you build deck stairs, the stair calculator is very useful and provides all of the information necessary to align the form for the lower landing to the deck. Using the diagram below for reference, notice that the Total Run [G] - 52 1/2" (1334 mm) plus 36" (914 mm) determines the distance of the inside face of the outer form member from the deck framing.
Once the form for the landing is in position, temporary stakes (nailed to the outside of the form) can be used to hold it in place and keep it square, level, and aligned with the deck frame. Once the landing's form has been secured, double-check the Total Rise [A] again. If it has changed, run it through the Stair Calculator again before laying out and cutting the stringers.
Install support posts and footings on the deck at the location of the deck stairs as indicated in the drawing below. The posts should be a minimum of 36" apart (the minimum width of a run of stairs). Install 2x8 (min) framing between the posts (to support the upper end of the stair stringers), directly under the outside joist of the deck. Add corner bracing to the new framing as indicated in the drawing below.
On the outside of the deck, at the location of the stairs, measure down 8 5/16" (211 mm) from the finished height of the deck, on each side of where the stringers will be attached, and make a mark with a carpenter's pencil. Using a level or a straight-edge, draw a level line to connect the two marks. This line will be the height of the top step of the stringers (this measurement is from the Stair Calculator results - Stringer Position [H]). Note that once you add the treads to the stringers, this step will be the same height as the others (Typical Step [F]).
Attach a stringer to each side of the deck framing (up to the level line), using an approved joist hanger. The stringers should be no less than 36" (915 mm) (outside-to-outside) apart. Notch the inside stringer(s) (as shown below) so that a 2x4 brace can slip under the front step. The 2x4 brace should be anchored to the concrete landing using concrete anchor bolts. If you only have one inner stringer, center it between the two outside stringers.
Note: Stairs can be built wider than 36", but additional stringers will be required. The additional stringers should be spaced evenly between the outer stringers and not more than 18" (457 mm) apart.
The diagram above shows the finished stairs with concrete already poured. This is just for example purposes, so that you can see how the stairs are aligned and attached to a lower landing. If your stairs has a Total Rise [A] of 30" (762 mm) or more (and our example does), a stair rail or guard is required. You would need to set the lower handrail posts before pouring the concrete.
These are the basics of building deck stairs. To continue with the handrail design and construction, navigate to Stair Railing.
For deck design and structural information, check out the Prescriptive Residential Wood Deck Construction Guide, by the American Wood Council.