How to Reinforce Staircases

Examine the underside of the stairway with a flashlight. If there is a finished ceiling attached to the underside, you will need to remove it to access the stairway's framework. Cut along the edges of the ceiling with a sharp utility knife. Using a hammer, knock out one of the corners out of the section you cut, put your hand in the hole, and pry the drywall off the bottom of the stairs.

Look under the stairs at the framework. The diagonal boards underneath the staircase that support it are called stringers. Treads are the horizontal piece of wood that you walk on when you go up and down the stairs. Risers are the vertical piece of wood that covers the space between the treads.

Drag a stud finder against the wall (or walls) underneath the staircase to locate the studs. Mark their location with a pencil. If you do not have a stud finder, you can also find the studs by tapping a horizontal series of nail holes through the drywall until you hit a stud.

Drive 3-inch-long screws through the stringer (or stringers) located against the wall at each wall stud location. The screw should go through the stringer and into the stud.

Spread a bead of glue on a strip of wood, and attach it into an underside corner where the top of the riser meets the underside of the tread to reinforce the connection between the treads and risers. Repeat for each step.

Test the fit of any shims that are present between the treads and risers and the stringers by trying to wiggle them back and forth. Some staircases use shims to adjust and tighten staircase components. If you find any loose shims, tap them in tightly with a hammer.