When you are building a wood and stone deck, or any deck for that matter, stairs serve a very essential part of them as they provide external or internal access to the deck. Your deck is easily as safe as your stairs are which is why you need to take into consideration how long your stair stringers should be and how they should be cut.
A stair stringer is a vertical piece of board that forms a platform or an exoskeleton for the risers and the treads to be attached to it properly. Different designs and styles of stringers can be combined to create an endless variety of stairs, it all depends on whether it will provide the utility that you require.
A stringer can run on the side of a staircase or even the center of it, again it is one of the host of many decisions that one has to make when constructing stairs. When located on either side, the inner stringers are situated against the walls while the outer stringer is situated towards the side of the wall. Your stairs, stair stringers and how they are arranged depend in a huge way on how your deck designs.
Read more: Building Box Steps and Stair for Decks
You might need to confer to your local safety and compliance code for details on what is allowed on a stringer for deck stairs. The riser and tread on a stair should be of a consistent height. The first thing that you should do is to figure out the overall height of the stairs by extending a level above the finished surface of the deck over the surface of the landing and measuring the two elevations. This would give you a rough idea of how much the rise and tread would be for the stairs.
Steps for Cutting Stair Stringers
Doing the Math
Assume that the overall rise of the deck stairs is 25 inches. The largest riser height at each step that most building codes would allow is 7 ¾ . Dividing 25 by 7 ¾ and rounding this number up would give you how many risers you would have in the stairs. The general formula for this would be:
Number of risers =Overall rise / maximum riser height
Make sure you round this off on a ceiling basis as in 3.2 should be rounded off to 4. To find the individual riser height you should divide the overall rise by the number of risers.
From our earlier example: 25 / 4 = 6.25
We should also consider the tread depth when making calculations for the risers. The minimum allowed by most building codes is 10 inches however the deeper the cut the longer a notch cut is required for the stringers which would weaken them.
Selecting Stringer Stock
Stringers may always need to be cut from 2x12 pieces. Notching smaller stock of wood would create unsafe stairs as they can collapse since anything smaller than this would not be able to bear the burden of the stairs.
When you are selecting a stringer stock, allow about 14 inches for each step. Look for straight stock with as few knots as possible, You would need at least one stringer for every 16 inches stair width. If you are using synthetic decking for your treads then sometimes stringer need to be spaced more than 12 inches apart as anything more than that would compromise the structural integrity of the stairs.
Laying out the Stringer
First you should lay a straight piece of 2x12 on sawhorses. Afterwards you should hold a framing square with the rise dimensions that you have calculated on the tongue and the run dimension on the blade intersecting the edge of the 2x12. You should clamp a scrap of wood to the underside of the square to serve as a guide and then mark out the first cut you would make with a pencil. The longer line would be the tread cut and the shorter line would be the riser cut. Keep moving the square up the stringer aligning the next tread with the next riser. Continue doing this until you have all your treads and risers marked out.
Adjusting the Stringers for the Tread Thickness:
If the bottom riser were to be cut at the full height of 6 ¼ inches, place the bottom tread to increase the height of that first step by thickness of that the tread. If your tread, let's say has to be 1 inch thick, the bottom step would be 7 ¼ inches instead of the usually 6 ¼ inches. This makes it unsafe and possibly a code violation.
Be sure to check out our deck design tool which would help you in area and height length calculations.