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Stair Stringers

Posted: Fri Aug 09, 2019 7:33 am
by Dave_88
Hello,

I am looking at building some interior stairs and just wanted guidance on making sure I am doing the stringers properly.

The total rise is about 10 feet and total run is close to 15 so they will be pretty long and I haven't seen a firm rule on how much "meat" should be remaining in the stringer after you cut the notch out.

I was originally thinking of using 3 2x12's for stringers but I've received some comments that for a run this long I should use LVL beams and even consider adding a fourth stringer for added strength (stairs are only 3ft wide and that sounded a bit overkill to me but I'm not an expert).

Any advice would be appreciated, Thanks!

Re: Stair Stringers

Posted: Fri Aug 09, 2019 8:08 am
by A. Spruce
First, I would recommend getting a copy of The Stair Builders Handbook, as it covers the hows and whys of stair building, and more importantly, has cut tables that take all of the calculations and guess work out of notch measurements.

Second, you need a framing square and a set of stop blocks so that you can do easily repeatable notch marks. The provided link is to show you what you're looking for, not necessarily to the exact product to purchase.

Is there a reason that the run has to be that long, because that is awful long and won't leave much left of the stringer once it's cut. If you are locked in at this length, then I would suggest adding a 2x6 backer under each stringer to carry the weight, as the stringers themselves will be too compromised to do it alone. 3 stringers will suffice for a standard 3' wide stair.

Re: Stair Stringers

Posted: Fri Aug 09, 2019 8:39 am
by Shannon
quick calculations:
120" total rise

17 rises of 7-1/16"
16 treads of 8" (plus1" nosing)
total run of 10'-8"

This is still a pretty easy to climb stair slope.

Re: Stair Stringers

Posted: Fri Aug 09, 2019 9:09 am
by Dave_88
Yes sorry I think I said run when what I meant was the total length of the stringer.

Re: Stair Stringers

Posted: Fri Aug 09, 2019 9:22 am
by Dave_88
Those calculations are actually pretty close to what I was planning. Do you think 3 2x12's would be fine in this scenario or would you go with LVL's?

Re: Stair Stringers

Posted: Fri Aug 09, 2019 2:13 pm
by Shannon
How much wood is left behind the cut out for the stringer? If its less than 3-1/2" measured perpendicular from the under edge of the stringer then you could either use LVL or add 2x4 stiffness on the back side of all singers as Spruce suggested earlier

Re: Stair Stringers

Posted: Fri Aug 09, 2019 8:13 pm
by A. Spruce
Dave_88 wrote:
Fri Aug 09, 2019 9:09 am
Yes sorry I think I said run when what I meant was the total length of the stringer.
Yeah, run and stringer length are two totally different things.

Without consulting the book I mentioned earlier, I can't say what the riser height should be or the stringer length. I don't do enough stairs to know how to do it without the book and cut tables.

I don't remember if these are interior or exterior stairs. If exterior, use pressure treated material for the stringers and then treat all the cuts with coppernapthenate or similar preservative to prevent rot.