Listen up, class! This quick tutorial will rid you of any
math anxiety.
How To:
Estimate step dimensions
Lay out and cut stringers
Assemble the parts
Whether
you’re replacing an old, rickety set of deck stairs or building a set for your
new deck, deck stairs are among the most challenging projects for the average
do-it-yourselfer to tack-le. One little mistake in calculations or layout and
you’ll wind up wasting lots of expensive wood, or worse, you’ll build a
downright dangerous set of stairs.
But building a strong, safe set of stairs is doable if
you meticulously follow the layout and cutting rules outlined in this
story.
Estimate the Landing Zone and Do the Math
You almost always have to design site-built stairs
yourself because the number and height of the steps will vary with the
landscape. Begin by drawing a side view of your site and adding dimensions
(Fig. A). That usually means going through the cal- culations a few times to
determine where the stairs will fall and to figure out how long your skirt and
stringer material needs to be. This sounds complex, but if you work through
it a few times and rely on your sketch, it’ll become
clear.
Here’s what to
do:
First determine the approximate height “X” (Fig. A).
Start by estimating where you think the last stair will fall by using a
40-degree slope (Photo 1). Rest a straight board on the deck and level over to
that spot and measure down to the ground. That’ll be the approximate height of
the stairs, “X.”
Now find the approximate number of steps. Divide “X” by 7
in. (an approximate step height) and round off the remainder, up if it’s .5 or
more, or down if it’s less than .5. That’ll give you an approximate number of
risers (Fig. A). The actual recommended riser height is 6-1/2 to 8 in., but
you’ll determine that later. If the riser height is too short, redivide “X” by
8 and start again.
On uneven ground, find the number of treads so you can
find the exact stair landing point. Simply subtract 1 from the number of
risers. (There’s always one fewer tread than risers, as you can see in Fig. B.)
Then, multiply by 10.25 in., the ideal tread width for two 2x6s, to get the
total run.Measure out that distance from the deck to find the exact landing
point. From this point, you can mea- sure the exact stair height and determine
the stringer and skirt length.
Measure the exact total rise (Photo 1). Divide the height
(X) by your estimated number of risers to find the exact riser height. The
figure will usually fall between 6-1/2 and 8 in., the ideal range. Use this
figure for your stringer layout (Fig. B). If the riser height isn’t in this
zone, add or subtract a riser and divide again. This will change the number of
treads and shift the landing point, so remeasure the exact height and divide
again.
Draw a sketch (Fig. B) to confirm the plan in your mind
and lay out the first stringer (Photos 2 and 3) using the exact riser and tread
dimensions and your framing square.
Plan to establish a solid base at the landing point. The
base can be a small concrete slab, a small deck or even a treated 2x12 leveled
in over a 6-in. gravel base. After you cut the stringers, use them as guides to
position your landing.
Cut and mount the stringers by following
our photos. In your layout (Fig. B), note that:
The top tread is 3/4 in. shorter than the other
treads.
The bottom riser is 1-1/2 in. shorter than the other
risers. Be sure to test-fit the first stringer (Photo 4) before you cut the
others. If you made a mistake, you’ll at least be able to save
the other two
2x10s.
FIG. A: Rise and Run Sketch
FIG. B: Stair Layout Sketch Click image to enlarge.
