Basement stair

benjamincall

I'm building a return stair to the basement. I have a couple of questions:

1) I'm guessing I should build the staircase before I carpet the basement, i.e., I want the stringers sitting right on the slab, not the carpet. Will the first tread need to be 1-7/8" higher than the rise on the other steps to account for the 5/16" dimpled membrane + 3/4" Advantech + 7/16" carpet pad + ~3/8" carpet?

2) How do you get straight, true stringers when you don't have a kiln, a planer, or a year to wait for your lumber to dry? Has anyone tried prefab steel stringers?

mrgins

Calculate your total height from finished basement floor to finished first floor. I would place the stringers on top of the floor sheathing. Lumberyard material is already kiln dried enough for this project. The only adding/subtracting to be done is taking off the thickness of the tread from the bottom of the stringers, and adding it to the rise of the top of the stringers

benjamincall

Thanks for the quick response!

Finished basement floor would be measured from the top of the carpet pile?

The reason I hesitated to place the stringers on the AdvanTech is that it will be sitting on top of the dimpled membrane.

So, if I build the stair on top of the sheathing, I don't need to take into account the fact that the finished floor (carpet in this case) is sitting higher than the bottom of the stringer?

mrgins

Some people may have different ideas, but I would place the stringers right on top of the advantech. For the finished floor, I'd go from the top of the advantech as the carpet will compress as you walk on it. You could probably remove 1/2" from that total if it works out better for your riser measurements if you had to.

jomama45

I'm not a carpenter by trade, but I wouldn't set the stringer on the dimpleboard, as the bottom of the stringer get's most of the weight & is likely to compress & shift on the dimpleboard. I also wouldn't add to the first riser more than maybe a 1/4" for carpet. As stated, carpet compresses. Maybe a seasoned vet can weigh in on this, but I don't think they take carpet into account.

benjamincall

You say you wouldn't put it directly on the membrane. Do you think the AdvanTech secured with tapcons would distribute the weight sufficiently to prevent compression of the Delta-FL membrane?

benjamincall

Does anyone have an opinion about whether or not I should place stair stringers on top of Advantech with Delta-FL underneath? Do you think the rigidity of the Advantech and the Delta-FL's compressive strength of over 5200 psf would be sufficient to support the force transferred through the stringers and the landing framework?

Should I cut the stringers short and place them on a flat 2x12 on the Advantech?