Undertaking a wood stair construction can be very complex for a novice builder. It requires precise measurements, math, and the patience to go slowly and get it right. This article will help go over the planning stages that you need to have in advance of building any wood stair in your home. Having a solid plan will save your hours of aggravation and will eliminate getting halfway through your build only to discover something, somewhere doesn't fit.
Step 1- Determine the Total Rise
The first step in making your staircase plan is to make sure that you have enough room to build the type of stair you have in mind. Stairs do have some dimensional flexibility, but one measurement that has no flexibility is the total rise of the stairs. The total rise is the height of the stairs from the finished floor on the bottom to the top of the finished floor upstairs. You need this total rise number in order to figure out how many steps your stairs will have and the height of each riser. Let's say that you measure a rise of 108 inches. You divide 108 by 7 to get 15.43. Since you can't have half a step, go ahead and round down to 15. Then you take 108 and divide it by 15 to get 7.2. So your risers will be 7 and 1/4 inches.
Step 2 - Calculate the Total Run
Now to calculate the total run we need to determine the depth of each tread. Most building codes require a minimum 9 inch tread depth. That being said, a much more comfortable tread depth is 10 inches or 11 inches. As a general rule the wider the tread the shorter the riser. Comfort/safety formulas have been developed to match tread depth of the riser height. The best formula to go with is the riser height + tread depth should equal between 17 inches to 18 inches. Since you know your risers are 7 and 1/4 inches then your tread depth should be 10 inches to fall within that range. To calculate the total run of the staircase, (the horizontal length of the proposed staircase), we multiply the number of treads (the number of treads is equal to the number of risers minus 1 (the bottom floor takes the place of one tread), in this case we would require 14 treads for a total run of 140 inches. At this point you should determine if you have enough space for the landing at the bottom of the staircase. The common rule is that the landing space should be at a minimum the same length as the width of the steps. If the steps are 36 inches wide you should have at a minimum 36 inches of landing space. With a 48 inch wide staircase you should have a minimum of a 48 inch landing space.
Step 3 - Calculate Headroom
Now that we have determine both rise and run, we need to determine if there is sufficient headroom. The calculation for determining headroom is: Headroom = [(length of stairwell ÷ tread depth) x stair rise] - floor thickness. Just as an example, we will assume that we have 133 inches as the length of the stairwell and a top floor thickness of 10 and 3/4 inches. Headroom = [( 133 ÷ 10 ) x 7 1/8 ] - 10 3/4. This leaves a headroom of 84 inches. Building codes requires a headroom of at least 80 inches, so you will definitely pass code with these calculations.
Step 4 - Outline Materials
Now that you have all of your measurements, you need to make sure that you have already secured a building permit for your stairs. If so, then you can go on to purchase the needed materials. Thanks to your measurements, we know that you will need 14 treads that are 10 inches, 15 risers that are 7 and 1/4 inches, and 3 stringers. For the stringers length you can calculate with Total Rise + Total Run = Length of Stringer. You can purchase pre-cut stringers if you prefer, because just a slight discrepancy with one of the 3 stringers can make you have to tear down and do everything over again. You will also need some 2-by-4s for the kickboard and ledger board. Don't forget that you will also need to choose balusters, newel posts, handrails, and any decorative trim and hardware. You need to purchase enough balusters so that they are close enough together that they would not let a 4 inch ball pass through. With the measurements and a supply list, the difficult part is mostly over. Now you can just work on building your new wood stairs.