- Q.Although code inspections are not routinely done in the rural area where I work, I want to make sure a winder stair I am building to access the upstairs of a storage building meets residential code — just in case the space is ever used as a living area. According to the IRC, you need a minimum 10-inch walk line 12 inches from the inside edge of the tread, and the minimum allowable tread width is 6 inches. Would this proposed layout (illustration, top right) meet code? All the winders are 6 inches wide at the narrow end, except for the last one, which is wider as the stair transitions to the final straight-run treads. The corners are the part I’m not sure about; the walk line is 10 inches along a line pulled diagonally from the corners.
A.Bruce Abernathy, a stair builder in Niceville, Fla., responds: First, keep in mind that the stair code doesn’t apply if the attic is used only for storage. There’s nothing in the code about drop-down attic stairs, for example. But you’re wise to cover the bases now, rather than have to rebuild later. (A local builder informed the inspector that the space above a garage he was building would be used for storage. The inspector didn’t buy it: When he saw that the “storage space” had finished oak flooring and crown molding, he red-tagged the stairs.)
In my opinion, straight stairs are the most easily navigated, and the fewer winders the better. But if you don’t have the space, you don’t have the space. Your layout should meet code; I’ve included a page from the Stairway Manufacturers Association’s interpretation of the IRC, which shows a variety of winder configurations, including one similar to yours (illustration, below).
Excerpted from the Stairway Manufacturers Association’s Visual Interpretation of the 2006 International Residential Stairway Codes
You can build your stair directly from your plan. First make a full-scale drawing and transfer the layout to the surrounding wall framing. Then use what I call a riser beam, where the risers are 2x8s ripped to match the rise, supported by studs or other framing at each end. I cut the treads so that they are flush with the face of the lower riser beams and glue and screw them to the bottoms of the upper riser beams. I then add extra support under the upper riser as needed.