Box style stairs are popular for very low decks and transitions between levels of tiered decks. Many deck builders use this technique to build a wide set of stairs across the front or side of deck. Box stairs do not use cut out stair stringers like traditional stairs. Box stairs are essentially a series of pressure treated wood boxes that are stacked on top of each other to create a short run of stairs. This method is easier to build and sturdier for stairs with up to 3 steps. Stairs with more than 3 steps should be built using stair stringers.
The first step is to measure the height of the stairs to determine the number of stairs you need to build. The maximum riser height is 8" and the minimum tread depth is 10". Most deck builders use 2x6 material to frame the stair boxes and use (2) 5/4x6 deck boards for each tread with a 1/2" overhang over the riser board. Cut the sides of the boxes and fill in the interior with blocking every 16" on center for wood decks and 12" on center for composite decks. Finish the stair boxes by installing the decking to create the treads. Use strap ties to connect the individual stair box frames together and secure the stairs to the deck frame using bolts.
We recommend installing frost footings for box stairs that will land on the ground. Just set a 4x4 post on top of the footing and attach it into the inside front corners of the box stairs. These posts can extend past the stair as a rail post. This will prevent the stairs from moving and shifting due to frost heave.