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PCI
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Discussion Starter · #1 ·
I am writing a proposal for a set of stairs on an existing deck. The deck is 11' tall, with a proposed rise of 7.33" and a run of 10.25". I come up with 18 steps and propose 4-2x12 treated stringers approx 9" oc. (tread 36" wide)

How do I calculate a live load for this set up? I believe the IRC specs 40lbs, but I can't find anything in regaurds to load calcs tables or throat minimums.
 

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Windwash
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I am writing a proposal for a set of stairs on an existing deck. The deck is 11' tall, with a proposed rise of 7.33" and a run of 10.25". I come up with 18 steps and propose 4-2x12 treated stringers approx 9" oc. (tread 36" wide)

How do I calculate a live load for this set up? I believe the IRC specs 40lbs, but I can't find anything in regaurds to load calcs tables or throat minimums.
You will need 5 stringers to go 36" wide at 9" on center I think.

I don't know the calcs but I do know that those stairs will be bouncy and will be sagging from the get go. You will either need a landing of some sort (straight or 90 degree turn) or will have to put midspan support posts with their own footings. IMO landings feel more comfortable to go down than long straight stairs but they do add to the cost.

Edit comment: I am assuming some sort of non structural composite decking. If using 2x treated or cedar for treads it will be stiffer than pvc/composite.
 

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General Contractor
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Yes, 40 PSF uniform load and 300 LB concentrated load...
 

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GC/carpenter
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Yep, 5" throat minimum. Although I've never had an inspector measure that, they are always more concerned with the stair rails.
 

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PCI
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Discussion Starter · #7 ·
Thanks all, same here with the inspector being more concerned with the rise measurements and the continuous damn handrail.
 

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PCI said:
I am writing a proposal for a set of stairs on an existing deck. The deck is 11' tall, with a proposed rise of 7.33" and a run of 10.25". I come up with 18 steps and propose 4-2x12 treated stringers approx 9" oc. (tread 36" wide) How do I calculate a live load for this set up? I believe the IRC specs 40lbs, but I can't find anything in regaurds to load calcs tables or throat minimums.
too bouncy, I remember building a set of deck stairs 9' tall three in a half feet wide with two stringers sistered on each end and two in the middle to make six total stringers, all with treated 2x12. It ended up with about a one inch bounce in the middle. I nailed a 2x6 stringer reinforcement on each one and it stiffened them up pretty good. You have a long set of stairs if it's just a straight run, no middle support and not attached to the building. You'll need to think of some way to stiffen that center. You have a lot of options like the apartment style steps with two beams and some precast steps can span a long ways. Other options; add a landing or beam in the middle, order 2x14s, attach non-notched stringers at the ends, or you can simply add a couple more stringers with a 2x6 stringer reinforcement on each one.

Also remember code is 36" wide between any finished material. If you have handrails sticking out then a 36" frame for your stairs won't cut it.
 

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Eater of sins.
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If it helps you can think of your stringers as roof rafters.
Use the IRC wood frame construction for roofs span tables.
The depth of the RR/Stringers are regulated by the non-cut depths of the bottoms of the stringers.
For your situation, you have an 18' span say 40 lb live load, 10 lb. dead, your effective RR/stringer depth is somewhere around a 2 x 6. look up in the tables for a 12" spacing for 2 x 6 span length. You will no doubt need a "purlin" at about half way for that span.
This assumes a delta or deflection of 1/180.

Andy.
 

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Somebody would have to be paying me some serious money to design and build something other than a prescriptive stair. Just about all I do require an engineer's stamp, even if it's prescriptive.
 

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diplomat
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If it helps you can think of your
For your situation, you have an 18' span say 40 lb live load, 10 lb. dead, your effective RR/stringer depth is somewhere around a 2 x 6. look up in the tables for a 12" spacing for 2 x 6 span length. You will no doubt need a "purlin" at about half way for that span.
This assumes a delta or deflection of 1/180.

Andy.
Something seems off here.
 

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I've built a lot of long steps with and with out supports. They all have a lil bounce regardless of how you modify. The 1st set was in exterior grade lvl's came in at about $1000 each and I needed 3. So I went fir steel cost me $1200 for c-chanel and diamond treads.

Then I started making dbl 2x12's for the outers and single 2x12 with 3/4 ply glues and screwed. total of 5 stringers. Also have used 4 2x12 all glued and screwed with 3/4 ply. 0 difference in bounce in comparison to the extra 2x. Much less weight to through around and easier to rougher the ply against the 2x12. They also get a 2/coat sealant before there dropped in.
 

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11' rise with 18 steps, you have about 18' stringer, that is one long set of stairs. If I was building a deck like this, I would definitely split that run with a landing... doing that IMO not only will it make a more comfortable stair, it will look more attractive.
 

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11' rise with 18 steps, you have about 18' stringer, that is one long set of stairs. If I was building a deck like this, I would definitely split that run with a landing... doing that IMO not only will it make a more comfortable stair, it will look more attractive.
Greg, sounds good but where I could ever try and fit another 3ft in my world...;)
 

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11' rise with 18 steps, you have about 18' stringer, that is one long set of stairs. If I was building a deck like this, I would definitely split that run with a landing... doing that IMO not only will it make a more comfortable stair, it will look more attractive.
If not this.

I would go with engineered prefab.

Whatever you do, you don't want to make the news with a collapse
 

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I didn't take any pictures of this process when we did it 5 or 6 years ago but my brother and I did this on a project with a long run of stairs, I'd do it again in a heartbeat if we had another long run stairs that I didn't use steel for.
The first thing to do is to nail a 2x2 onto the 2x12 and layout like normal, after the layout is complete take the 2x2 off, then cut the stringer as normal.



You'll end up with a funky set of stringers but then you use 2x8's (ripped to rise measurement) as your riser, that acts to support the edge of the deck board as well. between the 2x8 risers nailed to the stringers and all the additional meat from moving the notch up it's a very sturdy set of stairs. You can always add 2x6 or 2x8 strongbacks to it as well, or you can add more stingers, whatever makes you happy.



We always install a fascia that covers the ends of the boards so the missing triangle is never a big deal (I left it off the drawing for clarity).
 
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