Most of the custom homes I build have two stories and therefore require a set of stairs, and, except for a wrought iron spiral job, every staircase gets built on site. To make it easy to remember all the nuances of stair framing, I use a three-stage building checklist that helps me stay on track as I go along. The checklist is based on fundamentals that work on all sets of stairs, no matter what style.
Stair Calculation and Measurements
1. Check the Codes: Before I start anything I refresh myself on building code requirements for stairs and look for any recent changes.
2. Confirm Correct Stairwell Dimensions: I check the stair opening dimensions shown on the plans while the floor joists are being installed. If there is plenty of space for adjustments, I will often build to plan. On the other hand, if there is a wall above and aligned with the end of the stairwell, I check right away to make sure there is enough headroom under the header.
3. Ensure Proper Headroom: In order to build the stairwell correctly, I first need to determine the headroom at the head-out location. Check headroom by measuring diagonally between the header and a straight edge held across a few of the tread nosings, not vertically off the treads themselves.
4. Measure Rise and Run: To determine headroom and pinpoint the location of the stairwell header, I lay out a line on the wall or walls that the stair horse (also called a stringer or carriage) will be attached to. To arrive at this line, I need to measure the overall rise of the stair and overall run. I also check the plans to see where the stairs are supposed to end.
5. Follow Rules of Thumb: Try to keep the rise for each step no higher than 7-5/8 inches, and the run or tread no more narrow than 10 inches. It's good to build a comfortable set of stairs anywhere from 32 to 35 degrees, typically stairs where one tread and one riser add up to between 17 and 18 inches.
6. Determine Tread and Riser: Using the above information and the measured total rise and total run, I calculate the tread and riser needed to make the set fit in the given dimensions. The Construction Master Pro is my tool of choice for these calculations. I adjust the riser and tread until I get an acceptable slope and end up with the start of the first step close to the plan location. I can now pinpoint my headroom and have established the beginning layout for the stair horse.