Mark’s new house is comfortable, compact, and beautifully finished… but his builders made a couple of mistakes. First, the basement stairs weren’t built to code. A support column squeezes the basement stair landing too close to the top of the stairs, forcing risers about 8 ½ inches high when code limits them to 7 ½ inches. Second, the landing for the upper stairs is sagging due to inadequate support.
The obvious solution to the first issue is to move the support column – it needs to slide about 15 inches to make room for the basement stairs. So, let’s think like an engineer: what are the consequences of moving the column? One consequence is that the column no longer supports the end of the collector beam; it leaves a cantilever. An unintentional cantilever is never good, but 15 inches isn’t that big of a deal when the beam itself is 12 inches deep. We agreed to lag a stringer to a nearby LVL, reducing the load on the cantilever.
Another consequence is that the column no longer stands on a concrete footing but is supported by the slab directly. I went through a checklist to see if I was OK with that move. Slab construction? On grade. Soil underneath? Extremely dense glacial till, no risk of consolidation. Loads above? Just the first floor itself; the exterior walls are the only loadbearing walls in Mark’s whole house. I concluded the slab might be more susceptible to cracking, but structurally it could support the moved column just fine.
The second issue took a little more investigation. The exposed bit of landing support provided a big clue, and so did a nearby first floor joist that deviated from the pattern. My diagnosis was this: the upper stairs were built too narrow at first, and when they were widened an extra piece of landing was tacked on, resulting in another of those pesky cantilevers. I recommended Mark rebuild the landing as a single frame. He could do the job while the basement stairs were out, supporting the upper stairs temporarily from the basement floor.