Under stairwell bouldering

Climbers/handymen/women,

So, my wife and I want to make a little 45 degree training wall under a stairwell in the basement (pictured below). It would be about 38x123 inches, so only good for vertical training, but still worthwhile. Does anyone have thoughts on how to safely do this? I was thinking of screwing two sheets of 3/4" plywood, one above the other, on the underside of the staircase. I would then put T-nuts into it with various holds.

Problem#1: there is plaster covering the underside of the stairs so I can't see where the stringers are. Will they be just inside the outer wall? Is there always one in the middle?

Problem#2: even if we CAN find stringers to screw the plywood to, will it be strong enough to hold us making dynamic moves? (Especially toward the middle - away from the stringers, if there isn't a central one).

Any advice/help would be appreciated. This is really our only option outside of our hang boards. Thanks!

Luke

Here is how I would approach this project.

1. I would start by removing the sheetrock from the under side of the stairs. You should find three stringers (but maybe not if it is older construction). Plywood should be fastened directly to the stringers. If you don't find three stringers you will probably need to install horizontal blocking 16" on center between the outer stringers so that you have enough structure to mount the plywood.

2. Three stringers should be plenty of support for that width. When fastening to the stringers place a screw every 6 to 8 inches. That should provide plenty of holding power. I'd use self tapping deck screws.

Because the underside of the stairs is plaster, you'll probably have a hard time removing that to find the stringers. You could drill some test holes to see if there is a stringer in the middle.

Alternatively, you could bolt a 2x4 into that brick wall on the right, and another into the stud wall on the left. Then build a frame between them. 2x4 slats, 16" on center will hold up anything. if you do find a stringer in the middle, you could mount some little brackets on the cross-braces that tie to it.

I was thinking the same thing as Jeff. You could combine that with a few screws into the stringers for extra strength.

Thanks for all the advice, guys. Well, we decided to drill some pilot holes in the plaster and sure enough, there was a stringer in the middle and on both sides. So, we decided not to pull of the plaster, but rather to just mount the 3/4" plywood on top of it.

Unfortunately, we have a very old house (100 yrs old), and if any of you guys own old places, you probably know about how uneven things can be. When I put up the plywood and started putting screws through it I noticed that I had about a 50-75% chance of hitting a stringer in the middle and about a 75% chance on the sides unless I angled the screws, which would decrease some of the strength (I would think). I assumed that the middle stringer would be the same distance form the side walls all the way down, but apparently it's fairly uneven...

And... Now when we go up and down the stairs, one of them is noticeably moving... You can feel it wobble. This is new. It's all carpeted, so there's not a whole lot we can do.

So... We might die, but I appreciate all the help!

I have been thinking of doing similar, but under my back deck. My stairs have 3 stringers, but are not as wide as yours. Would one have to put 2x4s in between spaced out? Do instead of two long rectangles of space from top to bottom there would be many smaller rectangles?

Tyler - You mean 2x4s between the outside and middle stringers? If so, I wouldn't think that is necessary. The stringers themselves should be able to support the same weight from below as they do from above without additional support as long as you use enough screws. ...but I'll yield to anyone on this blog with more engineering/structural knowledge than me.