When you build a deck, spacing and sizing are both critical. Your measurements and layout need to be accurate, not only for the primary deck surface but for the smaller parts, like your deck stairs. Making strong, durable steps up to your deck requires careful measurement of the rise of each step, plotted together as one slope. This slope is framed by vital components known as stringers.
Stringers are the boards that show the rise and plane of each step your deck has. They are plywood framework that is installed before any other deck component. Their back surface is flat, a perfect slope leading up from the ground to the deck. Their front surface is toothed, cut out in the pattern that your stairs will take. Because stringers play such as important role when it comes step projects, they must be spaced carefully.
Standard Material Limits
Load support is important to your whole deck, but even more important to your stairs. When people walk up a deck, they exert much more force on the stairs than they do on the deck surface itself. Because stringers support some of this force, they cannot be spaced too far apart from each other. For a normal deck step, two stringers should be placed no more than 16 inches away from each other.
Lower Grade Materials
The type of deck material that you are using also plays an important role in load support. Your stringers cannot take all the credit -- high-grade wood materials will help support a lot of weight all on their own. But low-grade materials (below grade 3) and composite materials made out of a mix of recycled wood products have lower strength. For these materials, you should lower the stringer spacing down to 12 inches.
If you want wider deck steps for a better design style, you will need to add more stringers. A stringer in the middle of the steps allows you to double the 16-inch spacing requirement, creating a wider and more comfortable step style. For a stairway wider than 36 inches, you will need four spacers laid out on center.