Stair Planning Redux

Almost exactly a year ago I spent some time working out where the stairs would go and how exactly they would be configured. This was because the original design work I did had overlooked some issues that the architect caught, but in so doing he caused a lot of other problems. For example, in the approved drawings we have there’s only 5′ 10″ of headroom on the first floor landing. So I recalculated everything last year and had worked out a plan that was pretty good. I used that plan to position and size the basement stair opening.

However, since then I have leveled the first floor subfloor, which means the height from the first floor to the second is slightly different than it was when I made my calculations. Not only that, but if I plan to level the second floor as well I need to consider its height when it’s done rather than its height now.

Stair planning with minimum required headroom

Another factor is that I read up on load and span limits for the stair stringers. Since the opening for the basement stairs prevents me from having any intermediate support for the first floor stairs, they need to be able to span the whole distance to the first landing, which is nearly ten feet. That means I need to use 1 ¾” x 14″ thick, 1.55E stringers, which are bigger than I planned. That affects the headroom in the landing going down to the basement. Finally, the rise for each step must be equal and no more than 7¾”. The current rise floor-to-floor  averages about 10’11” (131″). I can’t fit more than 17 steps, so the closest rise match is 7 ¾” for a total rise of 131 ¾”. I guess I’ll just level the second floor to that height.

So, I went back to my model in Sketchup and started re-working the plans. I got a bit frustrated because I was spending a lot of time drawing things out just to figure out it wouldn’t work. I finally realized I need to draw the required headroom and clearance, so I could see how much space I needed.

Second floor stairs

Once I did that, it started to come together. It’s a tight fit between the multiple stories, roof slope, and other available space restrictions. There are a couple of things that are less than ideal. In the picture above you can see that the second floor landing will need to be notched so there’s enough headroom coming up from the first floor, but structurally it will be fine. There’s also the roof pitch clipping a triangle of headroom above that landing, and the stringers which are notched onto the edge of the landings rather than completely on top to provide enough space to meet code.

The good news is that I can figure this out on the computer and that it will all meet code requirements and I should be able to get a queen-size mattress up the stairs (and not bonk my head on the underside of the landing). Now I can get my LSL stringers on order and start framing the first floor landing.