Basement stairs installed by most home builders are often steep and narrow, usually built to satisfy minimum code requirements. For an entrance into your remodeled basement, you’ll want a stairway that’s attractive, safe, and convenient.
An existing basement stairway will probably have to be altered, and that’s not always easy. Changing the pitch of the stairs may not be a problem if there’s additional room at the bottom.
Enlarging the width, however, can be a major undertaking. Making a stairway wider is only slightly less complicated than cutting a new opening and building a new staircase. After you build a new stairway, fill in and cover the old stair opening, unless you want to have two sets of stairs to the basement.
Whether you alter an existing stairway or build a new one, follow the steps below. Remember that the rough opening must be wider than the finished opening by the thickness of your wall covering – usually ½ to ¾ inch for each side.
Cutting or Enlarging the Opening
Erect temporary support walls even if you’re only enlarging the opening. Reroute any plumbing lines (call a plumber for gas pipes), electrical wires, or ducts that run through the new opening. You may have to remove a finished ceiling to check for – and move – utilities.
Lay out and mark the perimeter of the opening on the floor surface above. Strip off any carpeting or tile (you can easily cut through most other types of flooring), then snap new cutting lines if necessary, and cut through the floor and subfloor with a circular saw. Set the saw depth to cut through the flooring, nut not into the joists.
Remove the flooring. If there is a finished ceiling below, drill holes at the corners of the opening, then connect the holes to mark the cutout on the ceiling. Remove the ceiling material within the marked area.
Working from above or below, extend the cutting lines down the joists. Cut the joists with a reciprocating saw. Measure and cut both the trimmer and header stock and fasten them with 16d nails staggered at 12-inch intervals. Cut stringers, treads, and risers, then hang the stairs in the opening. Frame in the old opening by installing new joists in joist hangers. Then install the new subfloor and finished flooring.
Building Platform Stairs
Platform stairs – two short runs perpendicular to each other – are useful in a tight space where you don’t have enough room for a single straight-run stairway.
Check your local building codes, however. Some codes don’t allow platform stairs. Others allow them, but set requirements for pitch, width, and other construction details. Make sure both runs of the platform stairs meet code. Pay particular attention to the pitch. Keep the angle of both runs between 30 and 35 degrees.
Lay out and cut or enlarge the opening if necessary. Frame the end wall at the bottom of the landing if required by your design or you local codes. Measure and cut platform framing members and assemble the platform by face-nailing through end joists or by hanging them in joist hangers.
Measure and cut studs and plates for platform support walls. Anchor the sill plates in the slab with concrete nails or powder-actuated fasteners. Assemble the support walls in place. Toenail the platform support to the support walls and face-nail it to the end and sidewall framing if there is any. Nail the lower ledger to the platform support. Compute the rise and run of the lower stairs and cut stringers, treads, and risers. Assemble the lower run, cut and install the ¾-inch plywood landing, and repeat to build the upper run.
If you plan to hang a door at the top of your basement stairs, be sure to include a landing for the doorway. An open stairway door cannot extend over the first step because opening it could knock someone down the stairs. Most local codes require such a landing.
