BUILDING YOUR OWN STAIRS Is a challenging, rewarding project. Dealing with the math involved, calculating angles, and making
the cuts may seem intimidating, but basic stairbuilding is within a skilled doityourselfer's grasp.
Before you do anything with stairs and landings, check with your local building department to see if you need a building permit. Also ask about code requirements for staircase
width, headroom, unit rise, unit run, landing sizes, and, fire blocking.
This article deals primarily with building interior stairs and landings, the overall objective of which is consistency in every tread and riser for safe use. Exterior steps are built in a similar way, except with deeper treads and shorter risers for safe use outdoors, where cumbersome boots, the weather, and other factors may interfere with stairclimbing.
The first step in building stairs is drawing the staircase. Show how the stairs will be connected
above and below, where landings will be positioned, and the thicknesses of the finished floors above and below. Building your staircase on paper allows you to identify and solve problems before making any cuts (Fig. 1).
MATERIALS AND DEFINITIONS
Materials include 2x12s for framing, 2x4s for supports, 2x4s and 2x10s for blocking, 1 x8s or plywood for risers, and standard stair treads (1 1 /8 inches thick, with a bullnose edge), dimensional lumber (2x6 or 2x12), or plywood (3/4inch CDX) for treads.
Total rise is the vertical distance from finished floor to finished floor. Total run is the horizontal distance the stairs cover from the face of the top riser to that of the bottom riser. Unit rise is the vertical distance from one tread to the next, and unit run is the horizontal distance from the face of one riser to that of the next. A stringer, or carriage, is the diagonal framing member (most often a 2x12) that supports the treads.
The rise/run formula is a guideline that states that unit rise + unit run = approximately 18 inches. Local codes may specify minimum and maximum values, but typically, a comfortable residential staircase will have a unit rise of 61/2 to 71/2 inches and a unit run of 101/2 to 111/2 inches.
BASIC STAIR CONSTRUCTION
A typical staircase is 3 feet wide, with walls on one or both sides. Three notched 2x12 stringers, spaced evenly, support the treads and risers. The outside stringers are set 11/2 inches away from walls by a 2x4 spacer rail (creating a pocket for drywall and a skirtboard). The stringers are attached to a header at the top and to a kickboard at the bottom (Fig. 2).
Treads and risers are glued to the stringers (using construction adhesive) and nailed or screwed in place. After drywall is applied, skirtboards and handrails are installed
RISE AND RUN CALCULATIONS
The following formula is used to calculate rise and run. Numbers in parentheses are sample values used to demonstrate calculations (refer to Table B).
• Measure the total rise between the finish floors (108 inches). If the finish floors are not yet installed, allow for their thicknesses when measuring.
• Divide the total rise by 7 inches (a comfortable unit rise) to arrive at an approximate number of stair risers (108 / 7 = 15.43 risers).
• Round this number either up or down to the nearest whole number and divide the total rise again by this new number to determine the average unit rise (108 inches / 15 risers = 7.2inch average unit rise).
• Convert this decimal number back into a fraction using Table A. Enter this number onto your worksheet under average unit rise (7.2 inches = 7 3/16 inches).
• Using the rise/run formula, calculate an average unit run by subtracting the average unit rise from 18 inches (18 inches  7 3/16 inches = 10 13/16 inches).
• Now convert the average unit run to a decimal equivalent (10 13/16 inches = 10.8 inches). Multiply the unit run by the number of stair risers to get the total run of the staircase (10.8 inches x 15 = 162 inches total run).
• Determine stringer lengths with this formula: (total rise) 2 + (total run) 2 = stringer length 2 (1082 + 1622 = 37,908). Figure the square root of the answer (square root of 37,908 = 194.7 inches), and divide it by 12 inches to convert it to feet (194.7 inches / 12 inches = 16.2 feet). Then add 10 percent, and round up to the nearest foot to find out the correct length 2x12 to buy (16.2 feet + 1.6 feet = 17.8 feet; rounding up = 18foot 2x12s).
• Determine the amount of riser and tread materials needed:
(15 risers x 36 inches x 7.2 inches = 3,888 square inches) + (15 treads x 36 in. x [10.8 in. + 1.2 in. nosing] _ 6,480 sq. in.) = 10,368 square inches = 72 square feet (three 4x8 sheets).
Note: There are 32 square feet in a 4x8 sheet of plywood and 144 square inches in one square foot. So 32 x 144 = 4,608 square inches per 48 sheet of plywood. If you're using dimensional lumber, round to the nearest 2foot increment. If you're using plywood, plan the tread cuts across the grain for strength.
BLOCKING
Walls that support and enclose stairways need blocking at several locations:
• Drywall backing2x4 blocks between each stud bay, level with the treads.
• Skirtboard and base trim backing2x10 blocks between stud bays at the top and bottom of the staircase.
• Handrail backing2x10 blocks every four or five stud bays, centered 36 inches above the top of the treads.
• Additionally, stairs enclosed on one or both sides by walls may need fire blocking installed between the wall studs. Fire blocking retards the spread of fire from one floor to another through the studwall cavities. Local building codes tell you how the blocking needs to be installed and whether it's positioned square or diagonally.
LANDINGS
A landing is a platform that connects two flights of stairs between floors. It is used when there is not enough room for a continuous stair run or to allow for a direction change (Fig. 3).
Most landings create an Lshape by forming a right angle between the upper and lower staircases. A landing should be large enough to support the upper flight stringers and provide enough room to maneuver furniture around any turns. A 3foot square landing is considered minimum by most codes.
For our example, the landing is placed halfway. The formula to calculate rise and run for the flights above and below the landing is the same as for a continuous run. Think of the landing as simply a large "tread," with the same unit rise as every other step.
• Calculate the rise and run of the staircase without a landing and draw it to scale.
• Using the scale drawing, determine the halfway point in the total run.
• Determine the height of the finished floor of the landing and mark that height on the wall framing. It will be an exact multiple of the average unit rise and, in our case, the same height as the top of the middle tread.
• Frame and install the landing. Use 2x10s, and remember that the framing will be positioned lower than the mark on the wall by the combined thicknesses of the landing subfloor and finish floor.
• Install the subfloor on the landing.
• Lay out the stringers for the upper and lower flights, using the calculations of rise and run from Step 1.
STRINGER LAYOUT
You'll have a tough time cutting and id_dil'iny stringers that are warped or severely crowned. Take the time to select straight boards with small, tight knots. 2x12s are a good size for stringers because they remain strong after the notches are cut.
• Set a 2x12 flat across a pair of sawhorses, with any crown facing toward you.
• Starting at the bottom, position a framing square so that the unit rise and unit run intersect the edge of the 2x12 facing you (Fig. 4). (A pair of stair buttons tightened at the rise and run marks on the blade and tongue of the framing square make layout
easier.)
• Mark along the outside of the square. The shorter line is the vertical plumb cut (rise); the longer line is the level cut (run).
• Slide the square until the outside of the blade/tongue intersects the pencil line just drawn and draw more lines. Step up the entire stringer, marking as you go.
• Cut the top plumb line (where the stringer butts to the stairwell header) and the bottom level line
(where the stringer hits the floor).
• Cut the notches accurately with a circular saw, making sure not to overcut the intersection of the two lines. Finish the cuts with a sharp handsaw.
• Your goal is to make every unit rise the same. To do that you may need to trim the bottom of the stringer to compensate for the thickness of the bottom tread. This is called dropping the stringer.
• If the bottom finish floor is already in place, trim the bottom of the stringer by the thickness of a tread.
• If the bottom finish floor is not in place and the stringer will rest on the subfloor, subtract the thickness of the finish floor from the thickness of the tread. Trim the resulting amount from the bottom of the stringer. If the finish floor and the
tread are the same thickness, no trimming is needed.
• Make the cuts for the top ledger and bottom kickboard, tracing around a scrap of 2x4 to mark the stringer.
• Install the ledger and kickboard. Kickboards applied to a concrete slab need to be glued down, using construction adhesive, and bolted.
• Testfit the stringer in all layout locations, checking for plumb and level.
• When you're satisfied with the fit, write "pattern" on the stringer.
CUTTING THE OTHER STRINGERS
• Lay the pattern stringer on top of 2x12 stock, making sure to align any crowns.
• Use a sharp pencil to trace the pattern onto each of the remaining stringers.
• Cut the stringers and nail the 2x4 spacer rails flush to the bottom of the two outside stringers.
• Set stringers in position, testing for
• alignment of all treads and risers.
• plumb/level cuts and the fit at the ledger and kickboard.
• uniform tread depth across all stringers.
• uniform riser height, especially to finish floors.
INSTALLING STRINGERS, TREADS, AND RISERS
• Nail or screw the stringers to the support ledger and to the bottom kickboard. Drill pilot holes to prevent the stringers from splitting.
Note: Do not nail the stringers to the wall studs. This may cause severe creaking when the wood shrinks and the house settles.
• Cut the risers and treads. Rip risers to the height of the unit rise. Rip treads to the length of the unit run, minus the thickness of the risers, plus any nosing (typically 3/4 to 11/4 inches).
For stairs enclosed by walls on both sides, the width of both risers and treads should be the same as the distance between the outside of the outer stringers, allowing room for the drywall and skirtboard to fit in the pocket left by the 2x4 spacers.
• Working up from the bottom, install the risers and treads. Start by fastening the bottom two risers in place, then fasten the first tread. Next, fasten a riser, a tread, a riser, a tread, and so on. To prevent squeaks, run a bead of construction adhesive where the treads meet the stringers and risers, and fasten the risers and treads with 8d ringshank nails or 2inch screws driven through pilot holes. The risers get two fasteners at each stringer location; the treads get three.
Note: Because of dropping the stringer, the first riser will often be a different width from the others. Size it accordingly.
• Install fire blocking between the studs at an angle, or as required by local codes.
• Install and finish drywall on the walls and under the stringers.
• Use the pocket from the spacer board to slip in a 1x10 or larger piece of lumber as a skirtboard on each side of the staircase to prevent scuffing the wall surface. Screw the skirtboard into the wall studs, and plug the screwholes for a better finish.
• Set a handrail on one wall at 30 to 38 inches from the front of each tread or as required by local building codes.
