When it comes to building stairs, it’s important that you correctly calculate the slope of the flight to ensure that it isn’t too steep. Whilst calculating the slope can actually be quite simple, most regulations are written in terms of the tread width and riser height. Once you have these measurements, you will know whether your stair slope is legal or not.
Step 1: Measure the distance of your treads (if they have nosing, exclude the width of this). If the treads are all uniform in size, you will only need to measure one but if they are different, you will need to measure them all.
Step 2: Measure the height of your risers, which is the distance from the top of one tread to the top of the next. If the risers are all uniform, you will only need to measure one, otherwise you will need to measure them all.
Step 3: Divide the riser height by the tread width, then calculate the inverse tangent (or the arctangent) of the result. This will leave you with the slope for building stairs.
At the end of the day, it is always best to aim for treads and risers that are uniform in size, as this will ensure an easier collection of measurements and more accurate results. If you feel that the slope is too steep or not steep enough, you should speak to the contractor in charge of building stairs and ask them how they plan on rectifying the problem.