Stairs 1: How to Build Stairs

Building stairs is a job that experienced carpenters know requires accurate measurements and diligent work habits. I'll attempt to guide you through the steps, pun intended, of staircase construction in a 'dwelling unit'.

Knowledge of how to build stairs is very important not only in the stairs being useful and looking good, but also in preventing accidents. Besides needing to be sturdy and wide enough, stairs need to be consistent. Each step must be exactly the same size as every other step. (see Figure 1)

The first thing to do is to measure the height where your stairs will go. This is your most important measurement. It is called the total rise. Every other stair measurement depends on it. The total rise is the vertical distance between the surface of the higher floor and the surface of the ground, sidewalk or the lower floor that the last step will be on (see Figure 2)

The total run is the horizontal distance between the edge of the upper floor and the end of the bottom step.

Each stair step has two basic measurements. The horizontal or flat part of the stair is called the run. The vertical height difference between two stairs is called the rise. The riser is the vertical part of the stair between a tread and the underside of the tread above it. The part of the stair that sticks out past the stair riser is called the stair nosing. The dimension of each stair depends on a number of factors. Your stairs can be steep or gradual. The rise of each stair can vary as well as its run. (see Figure 3)
 
 

Building Codes

Stairs and accidents often go together. Carrying a heavy, awkward load down stairs is an exercise in trust. Trust that the builder did a good job, that the rise of each step doesn't vary by much, that the next step down is where it should be, that the stringer is strong enough, etc.

Building Codes help the builder and everyone who uses his or her stairs. That's their purpose; not to make your life difficult with a lot of rules. A good builder knows his local building code.

The following table gives a summary of the 2015 International Residential Code for Stairways (Section 311.7). Your local building code is likely very similar.

*   The two starred measurements (Width handrail to wall and Width between 2 handrails) have a length in inches that is different to their lengths in millimeters. This is in the original document. All other conversions between inches and millimeters is correct.

The two variation items in the table refer to the maximum difference allowed between the smallest and largest riser or tread in the staircase.

For more info on Building Codes see my article Useful Stuff 5: The National Building Code
 

Relationship Between Stair Rise and Stair Run

To prevent the stairs from being too steep or too gradual (see Figure 4), there is a relationship or proportion between the stair rise and the stair run. The British Columbia Building Code (where I live and work) says the stair rise must have a maximum of 200 mm (7 7/8") and a minimum of 125 mm (5"); the stair run has a maximum of 355 mm (14") and minimum of 210 mm (8 5/16"); the stair tread depth has a maximum of 355 mm (14") and minimum of 235 mm (9 1/4"). The tread depth is the stair run including the nosing. The stair nosing cannot be more than 25 mm (1"). You should check the building code of your own region before building or renovating anything structural for your home.

An old adage says that for older people the ideal stair rise is 6" with a stair run of 12". An intermediate stair rise is 7" and the stair run is 11". The steepest stairs should be no more than a stair rise of 7 3/4" and a stair run of 10". Notice that in each case the stair run plus the stair rise equals 18". This is the simplest way of determining stair rise and stair run but the size of each stair is totally up to you as long as they are within Building Code ranges. The ideal stair run and stair rise for a dwelling based on a 92 1/4" stud, 3-1 1/2" plates, 2x10 floor joists and 5/8" subfloor is 14 rises of 7 5/8" and 13 runs of 10 1/2" with a 1" stair nosing.

The preferred angle of stairs is around 30 to 35 degrees. There are three generally accepted rules for calculating the ideal stair rise to stair run ratio:

1. The sum of two stair risers and one stair tread is 24" to 25"
2. The sum of one stair riser and one stair tread should be 17" to 18"
3. The stair rise times the stair run should be between 70" and 80".

To keep each stair rise the same size, you'll need to make some calculations. Follow these steps:

1. Measure the staircase's total rise (distance from the surface of the upper floor to the surface of the lower floor). If your measurement is in feet and inches then convert it into inches only. Example: 8'-10 3/4" is 8 x 12 + 10 3/4 = 106 3/4 or 106.75
2. Decide on the size of the stair riser you want for your stairs, say 7 1/2 inches.
3. Divide the staircase's total rise (measurement from 1 above) by the size of the stair riser you decided on: 106.75 / 7.5 = 14.23.
4. The result of the calculation will probably not be a whole number (one without a fraction). There will most likely be a remainder or fraction. Choose the nearest whole number to the answer of your calculation (in our example it would be 14). This is the number of stair rises in your set of stairs. Now to calculate the exact stair rise, divide your staircase's total rise by the number of stair risers (in this example it is 14 risers), i.e. 106.75 / 14 = 7.625 or 7 5/8".
5. As we previously mentioned, there is one less stair tread than stair riser, so in our example of 14 stair rises there would be 13 stair treads.

Dan, my brother and webmaster, made a simple stair calculator for you to find the exact measurements of your stair rise and stair run. See our Stair Calculator

Enough Room for Your Stairs?

It's a good idea before you start building the staircase to make sure the planned staircase can fit within the space that you have. Calculate the total run of the staircase by multiplying the length of the run of each stair by one less than the number of stair rises you calculated in step #4. I like a stair run of 10" to 10 1/2" for a stair rise of 7 5/8". At a stair run of 10.5" for 13 stair treads, the arithmetic is: 10.5" x 13 = 136.5" for the staircase's total run. Then measure the physical space within your house to make sure there is enough room for the staircase. Hang a plumb bob from the edge of the upper floor, where the stairs are going to be attached. Measure from the plumb bob to where the bottom of the stairs will be. Make sure there's plenty of room so the stairs don't run into a wall or other obstruction.

Allow at least 36" between the end of the bottom stair and a wall, if inside a house. If your measurement is too tight, try a stair run of less than 10.5" down to 10". Our total run in this staircase would be 10" x 13 = 130". We just saved 6.5". These calculations show the versatility in choosing different stair runs and stair rises. If room is still limited try taking off a stair riser, thus eliminating a stair. Remember though that you must stay within the maximum and minimum parameters for stair rise and stair run. Maybe move the obstruction or move the stair opening back in the upper floor if you have reached your maximum stair rise and minimum stair run. Installing a stair landing will change directions of your stairs, which can give you more room in many cases. (For more info on staircase landings see Installing a Landing in a Staircase)

Watch the staircase headroom also. (see Figure 5). If the stairs are in an opening cut out of a floor area, headroom is a factor. The staircase opening must be long enough to allow adequate headroom when coming down the stairs. The minimum staircase headroom under a beam or joist is 1.95 m.(76 7/8"). Now that we have determined our stair rise and stair run and checked for adequate staircase headroom, we can cut the stair stringers. (For more info on stair stringers see How to Cut Stair Stringers.)

Width of the Stairs

Nail the stair stringers in place, securely to the top floor trim joist and to the bottom floor, or to the side walls. Next is installing the steps or stair treads. In our stair example we chose 1" plywood for the stair treads. Since our stairs are inside a house and will be carpeted, we will choose a stair nosing of 1" giving us a stair tread width of 11 1/2". Rip the 1" plywood 11 1/2" wide and the length to match the width between the walls less 3/4" on each side for the drywall to slip down. The width of the staircase is important as well. The minimum width is 860 mm.(33 7/8"). I prefer a width of 36" if appliances or furniture have to be moved up or down the stairs. If your staircase is wider than 36" put in extra stair stringers to support the longer stair treads.

Outside Stairs

In an inside staircase the stair riser is usually closed, there is a board for the stair riser to attach the carpet or other finish to. This is different to an open riser staircase such as outside off a deck where the stair risers do not have a board attached to them. In this case the stair treads should be made from 2 x 4, 2 x 6, or larger to stand up to the weather. Also, on this type of staircase overhang the stair step 4 1/2 inches from the outside edge of each stair stringer on a 3 foot or wider staircase. (Example of stairs off a deck.)

Putting the Staircase Together

Back to our project. We have 13 stair treads ripped and cut to length now.

A tip to save your carpet is to round over the top edge of each stair nosing. Do this with a router, a belt sander or a block plane. It is easier to do this before installing the stair treads.

Let's rip the material for the stair risers. This can be 1/2" to 3/4" plywood. In new construction, there are usually scraps of 5/8" left from the sub-floor. Since our stairs will be covered with carpet let's use these. Rip the stair riser pieces 7 5/8" and the same length as our stair treads. Now start assembly at the bottom of the staircase. We discover that our first stair riser is too high, that's because we cut 1" off the bottom of the stair stringer. Adjust the first stair riser to fit the stair stringer. It should be 6 5/8", unless the depth of the floor covering on the bottom floor is different from the depth of the covering on each stair tread and on the higher floor. What you want is to have the exact same height of each step all along from the lower floor to the upper floor. In other words, if the depth of the lower floor's carpetting or tile is thicker or thinner than the material on the stair treads then subtract or add the difference to this lowest (first) stair rise.

Nail the stair riser on with some construction adhesive or use the adhesive and screws. Nail the next stair riser on, then put some adhesive on each stair stringer at the bottom stair and put some adhesive on the back edge of the stair tread where it meets the stair riser. Nail the bottom stair tread down to the stair stringer placing it tight against the second stair riser and from the back of the stair riser nail through into the stair tread. You can see that the stair tread is now supported by the stair stringer on each end and the lower stair riser supports the front while the upper stair riser supports the back - no squeaks here. Continue up the stairs following this procedure. When you arrive at the top stair riser, it will need to be trimmed to fit. If there is no nosing on your top floor to match your stairs, now is the time to put one in. I usually rip a nosing from solid lumber, say a 2 x 4, to match the overhang and thickness of our stair nosings. Glue and drill and screw this nosing on securely.

Stair Stringer Support

If your stairs were built outside and the stair stringers have no support under the middle of them now would be the time to put 1 or 2 posts under the stair stringers for added strength. Also if these stairs are hanging off a deck with a 2 x 6 trim joist, not much is there to secure the stair stringers to at the top. What I like to do is support the stair stringers with a 4 x 4 that goes from a concrete block or footing right up to above the deck level to form the stair handrail post. Below the stair stringers and tight up to them, nail a 2 x 4 or 2 x 6 ledger across the posts. Then nail a 2 x 4 across the posts near the bottom to prevent the posts from kicking out.

Stair Handrails

Stairs need handrails. These should be between 800 mm(31 1/2") and 965 mm(38"), measured vertically from the edge of the stair nosing (see Figure 6) to the top of the stair handrail. I suggest 32" as a comfortable height.At a staircase landing, the stair handrail should be 36" high and at a balcony edge should be 42" high. These measurements are for single dwelling residential construction (one family house).

Dave