Step Treads for Wooden Deck Staircase

How to install or replace step treads on outside stairs.  Determine the best size material for every situation and learn to turn them the best way.

Stair Treads

Each step must be a minimum of an 11″ deep tread according to the 2012 International Residential Code. This is also the case for most every other building code. This is not the same as the run. The run has to be a minimum of 10″. Although the run and the tread depth are closely related, they are not the same. For more on “the run”, click here.

For many carpenters it is standard practice to simply use a 2 x 12 for the tread and simply turn “the cup” down.

Notice how the tread is curling on the end.

There are too many problems waiting to happen when you try to use a single board for each step. Lumber this wide will most likely curl and possibly do all sorts of crazy things. It is simply far better to use two 5 1/2″ boards. This greatly reduces the amount of cupping and other distortions that may accompany weathering wood.

When dealing with the cups, while using two boards for the tread, the outside board must have the cup turned down. This is very important to reduce the risk of falls. The board on the back side should also have the cup turned down whenever possible. It is possible however to cheat on this a little bit, on the back side only, and turn an ugly spot down so long as the cup is not too bad.


The backings for any staircase should always be installed first. If the tread is first nailed down and then the backing

Even though the cups are turned wrong and the backing is not right you can still tell how much better it is to use two boards.

is applied, then this will reduce the depth of the tread you have to stand on by the thickness of the backing which will violate the building codes as well as practical building sense. Just remember that at the top of a drop step there is no backing so the thickness of the backing must be removed from the top run.