When building stairs for your deck you will also be expected to follow the IRC building requirements. These requirements are strictly enforced by building inspectors. The minimum width for stairs is 36”, but we recommend using 48” stairs wherever possible.The maximum riser height is 7-3/4” and the minimum recommended rise is 4”.The minimum stair tread depth should be measured at no less than 10”.The tread width and riser height shall not exceed the smallest by more than 3/8”.This means you will have to plan ahead to make sure each and every one of your stairs measurements are the same. In other words plan ahead so you aren’t left with a really tall or short last step because you will fail the inspection.
The first step in designing a set of stairs using stringers is to determine the overall height a flight must extend to. The height cannot be measured directly down from the deck at the stair location if the ground is uneven, instead measure from the location where the stairs will land vertically to the height of the deck floor. The maximum rise between adjacent treads in mainstream building codes is 7 3/4". Divide the overall height by this value and round up. This will yield the minimum amount of rises required for the stairway. Subtracting “one” from this value provides the number of treads (assuming the first tread is a step down from the deck). Once the number of treads is determined, the exact location the stairs will land can be discovered. Multiply the number of treads by their depth (minimum 10 inches) and measure out from the deck to where the stairs will land. Now determine the height from this point to the deck and adjust the rises uniformly as necessary. Once the riser height and tread depth is determined, you can begin building your stairs.
Open risers are permitted by code with a catch because they may not be large enough to permit the passage of a 4” sphere the same as rail infill rules. In most cases it looks nicer and is just plain easier to close the risers. You must maintain a minimum 6'-8" headroom clearance and provide stairway illumination at the top landing. Stair stringers should be cut from 2x12 pressure treated lumber and spaced no greater than 16" O.C. Not all composite decking material is approved for use on stairs.