Unless your deck is within a step of the ground, you will need to build stairs. Building codes usually are quite strict about stair dimensions, although exterior stairs are often afforded more latitude than interior stairs. Stair building lingo can be confusing at first. Rise is the vertical distance from one tread to the next; run is the horizontal depth of the tread. The total rise and total run are the overall vertical and horizontal measurements of the stairs.
For greatest stepping comfort, try to build deck stairs with a 6- to 7-inch rise and an 11- to 16-inch run. The large range in run distances is because you can use either two or three 2x6s for each tread. The deeper treads can be a safety feature when stairs are wet or covered with snow and ice. Stairs that are 3 feet wide are comfortable and safe, and may be mandated by your local code. Use three stringers on 3-foot-wide stairs. Although you can get by with two stringers on narrower stairs, the time and cost of making that extra stringer are minimal. If you build wider stairs, add an additional stringer for every 2 feet of stair width.
Tools: Hammer, straightedge, tape measure, pencil, level, framing square, circular saw, handsaw.
1. Prepare the concrete pad. Excavate and build forms for a 4-inch concrete pad set on 6 inches of gravel. Mix and pour concrete. Screed the surface with a 2x4, then smooth it with a wood float. Run a pointed trowel between the concrete and form boards', follow with an edger. After an hour, smooth the concrete with a steel trowel. Or, prepare a bed of tamped gravel at least 6 inches deep.
2. Find the rise. Use a level to extend the deck to the spot where the stairs will land (usually the pad or gravel bed). Measure the total rise and divide by 7 (the height of an ideal rise). The result, rounded to the nearest whole number, is the ideal number of risers for the stairs. Now divide the total rise by the number of risers to determine the actual rise for each step. For example, assume the total rise is 24 inches; 24 divided by 7 is 3.4. Round 3.4 down to 3 and divide this into 24. The result (8 inches) is the rise for each step. An 8-inch rise is on the high side so you can take the option of rounding 3.4 up to 4, then dividing 4 into 24, for a more comfortable rise of 6 inches (with 4 risers rather than 3).
3. Find the run. If you’re not constrained by space, choose a convenient, comfortable tread depth: Two 2x6s for each tread, with gaps between them for drainage, and a 1-inch overhang. The resulting run is IOV4 inches. Estimate the length of a 2x10 or 2x12 stringer you’ll need by measuring from where the stringer connects with the deck to the ground-level riser.
Choosing the Right Lumber for Stringers - Stringers carry the weight of the stairs, so they need to be large and solid enough to perform their job. You may be able to get by with 2x1 Os for deck stringers, but 2x12s are always the safer choice. Look for boards that are straight and relatively free of splits and knots. If the ends are split, cut away the split section before laying out the stringer. Check that no knots are loose. If they fall out after you build the stairs, they will not only be unsightly but may weaken the stringer significantly.
4. Make the stringers. For 3-foot-wide stairs, cut three identical stringers. Lay out and cut the first one, then use it as a template to lay out the other two. To lay out the stringer, place a framing square on a stringer so the 6-inch mark on the outside of the square’s tongue and the lOVfe-inch mark on the outside of the square’s blade both align with the top edge of the stringer. Mark the rise and run along the outside of the square. Move the square and repeat. Mark an additional cutoff of 1 1/2 inches off the bottom and add the amount of the decking overhang at the top.
5. Cut the stringers. With the layout completely marked on the first stringer, carefully cut it out with a circular saw. Cut only up to the layout marks. Where the tread and riser meet, the circular saw blade won’t cut all the way through. Finish the cuts with a handsaw. Set the stringer in place and check the accuracy of your layout. Once you’re assured all the markings are correct, use the cut stringer as a template for cutting the others.
6. Attach stringers to footing. On a gravel pad, attach two 36-inch 2x4s to the bottoms of the stringers and embed the 2x4s in the gravel. On a concrete pad, space outside stringers 36 inches apart, center the middle stringer, and attach with masonry anchors.
7. Attach stringers to deck. Stringers must be installed straight and square. The top should be level with the top of the joist, slipping directly under the overhanging deck boards. Use angle brackets or framing anchors to attach stringers to the joist. As with any structural bracket, use only the fasteners recommended by the manufacturer.
8. Attach the treads. Each tread is made of two pieces of 2x6 decking. Cut each 38 inches long to provide a 1-inch overhang on each of the outer stringers. Use a 10d nail to measure the gap between treads and between the back tread and the stringer. The treads should overhang the front of the stringers by 1 inch as well.
9. Build the railing. The stair railing should match the style of your deck’s railing as much as possible. Use similar balusters, spaced the same distance apart. One important difference, however, is that the handrail must be easy to grasp. This can be accomplished by setting a 2x top rail on edge so it can be grasped. Even better, place a 2-inch-wide cap on the top rail for optimum safety. Prepare and fasten posts and balusters as you did for the deck railing. Make plumb cuts on the top rail.
Caution! For Comfort and Safety, Add Handrails - Municipal building codes generally require a railing on stairs with three or more risers. But there is almost no stair that can't be made safer by adding a railing. Having a solid object to grasp when stepping from one plane to the next is a bit of comfort that most of us can appreciate. Take the trouble to add this safety feature, especially if your deck is going to be used by a chila or an elderly person. Think safety even if your deck has a one-step level change. Avoid stumbles by adding a strip of non-skid, yellow reflective tape to assure the step up or down will be seen by the user and a foot won't slip over the edge.
Use a solid stringer alternative. The strongest stairs are made with treads sitting on top of notched stringers. But some people don’t care for the appearance, preferring to mask the tread ends with solid stringers. You still need to lay out stringers, but instead of cutting them, you install wooden cleats or tread brackets to the inside of the stringers. Once the stringers are attached to the deck, treads are cut to fit between the stringers and are fastened to the brackets or cleats. If you use this method on a wide stair, you should still prepare a notched middle stringer.
Notched posts on solid stringers. Posts on solid-stringer stairs must be prepared differently as well. Notch the post if you like. Set it in place, checking for plumb, then mark an angled line where it touches the stringer (top and bottom). Cut the notch and fasten it with carriage bolts.