Stair stringers

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Forum topic by Clifford91 posted 03-26-2018 12:22 PM 576 views 0 times favorited 9 replies Add to Favorites Watch
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4 posts in 670 days

03-26-2018 12:22 PM

Hi all,

I’m new here, but have visited a few times for information. I’ve looked through many posts and haven’t found quite what I’m looking for so hoping for some general advice. Sorry if the post is long, I’m a detail person.

I am looking at building a set of fairly long outdoor stairs up a hill, from one pad to another, top and bottom both with cement landings. Vertical rise of 12 feet, horizontal distance of 22 feet (though I may make it 1-2 longer, that’s just the minimum).

I would have liked to use 4×12’s as stringers, but they are extremely expensive where I’m at, to the tune of 2-3x the cost of two 2×12’s the same distance.

I have in mind to use two 2×12’s on each side as stringers (so four in total), lagged together with staggered joints, and have a few questions.

The first being, can I make a run that long without any supports between the top and bottom? Will four 2×12’s support the weight? I can put one or two intermediate pylons in if needed, though I would rather not, just for asthetics.

My next question is am I okay to attach the faces of each stringer on each side right to each other (such as glueing) and then lagging, or would I be better to space them with shims and then lagging. This is mostly worrying about rot and moisture between the two boards. They will get treated either way, just wondering if spacing them reduces the load-bearing capability as a whole.

My last question is, if I do need to seperate the two stringer boards on either side, can I do so by putting the 4×4’s I’m going to use to support the railing in between the two stringers on each side? Is that too far of a gap that it will render the outer stringer useless in weight bearing?

Open to all ideas here. I’m not opposed to over-engineering things here as that’s my usual MO.

Thanks all.

-- Good with a hammer, marginal with a tape measure... Still not sure what that level is for...

9 replies so far

View Robert's profile


3602 posts in 2089 days

#1 posted 03-26-2018 02:22 PM

Why not use the 4×4 posts to support the stringer? You should have a railing, right? Then you don’t need to double up.

How wide is the staircase? You can support the middle stringer(s) with a concrete pad and post.

You can span the butt joint with a steel plate (look at the Simpson stuff).

I always use thru carriage bolts, not lag bolts on projects like this.

-- Everything is a prototype thats why its one of a kind!!

View Clifford91's profile


4 posts in 670 days

#2 posted 03-26-2018 02:43 PM

Thanks for the reply.

My reasons for not having supports in the middle is partly asthetic, I just think it would look attractive being sort of “free-floating”. The other is the terrain. The soil on the hill is clayey silt mixed with rather large cobble (2” up to 12”). Working it and either doing pads or pylons is very tedious. Just wondering if I can avoid that.

If I did do that, then yes the 4×4’s would support the stringers.

Most likely it will be 48”. I would like to go wider but probably wont.

Now that you mention it Im wondering if I could only do supports on the middle stringer,, and so keep them hidden and the appearance of a full span staircase on the outside.

I use the terms lag and carriage interchangeabley and probably shouldnt. I have in mind to use carriage bolts, thank you for clarifying.

Thanks for the response, again still just brainstorming.

-- Good with a hammer, marginal with a tape measure... Still not sure what that level is for...

View Ripper70's profile


1371 posts in 1517 days

#3 posted 03-26-2018 03:03 PM

Tony_S is the resident stair master around here. Hopefully, he’ll chime in with some useful recommendations.

-- "You know, I'm such a great driver, it's incomprehensible that they took my license away." --Vince Ricardo

View Snipes's profile


445 posts in 2853 days

#4 posted 03-26-2018 03:27 PM

I think 12’ is the max height from floor to floor per code, so you should be alright there. You could have 4×12’s milled up. If you sandwich 2 you could have moisture issues as you stated, I think you want to use .6 pressure treated if you do this. Probably going to need some support to keep the bounce down.

-- if it is to be it is up to me

View bdresch's profile


155 posts in 2216 days

#5 posted 03-26-2018 04:14 PM

Will you be getting permit/inspection of this? I ask because there are some very specific code details on stairs. If you are deviating from them you will likely need an engineers sign off to get it past an inspecter.

View Clifford91's profile


4 posts in 670 days

#6 posted 03-26-2018 05:37 PM

Snipes, does that apply for outdoor stairs which are not actually traversing from one floor of a house to another? Am I correct in assuming a landing of proper dimensions halfway up meets the requirement of that as well?

Bdresch, honestly I was not planning on having it inapected. But I am not opposed to it, or to building it to code. And I am not trying to do anything less than code, I want it to last as long as possible. I guess that’s just my question, “can I build it to meet code or more, the way I envision it?”

Just a reminder, as I’m not sure if it changes things, this is an entirely outdoor, free standing staircase, not attached to a structure.

Thanks again all.

-- Good with a hammer, marginal with a tape measure... Still not sure what that level is for...

View Snipes's profile


445 posts in 2853 days

#7 posted 03-27-2018 12:04 AM

Yes your assumption would be correct, residential construction 12’ landing to floor or floor to floor. Since its not attached to structure there should be no footing requirements either. I’ve only done freestanding down to lakes, put posts into ground 4’ and attach to those, which serve as newels also.

-- if it is to be it is up to me

View Tony_S's profile


1067 posts in 3691 days

#8 posted 03-27-2018 09:31 AM

Where to start here…?
22’ is a pretty long total run for a free standing staircase. With a 12’ total rise your looking at a 25’ long stringer and about a 29 degree pitch which is a pretty low slope as well. The length in combination with the low slope makes for a (free standing) stair that I don’t believe you would be happy with, short or long term.
You don’t mention what type of stringers you had envisioned using. ei. Closed(housed) or open(carriage). This will effect the strength greatly. What about risers? It’s an exterior stair, so I would assume at this point that you’d want an open rise stair? Possibly with half risers? How about a third(center) stringer? What about the width?
All these things effect the strength and stability of the stairs. On long runs like your suggesting, even the quality of the lumber you’re going to use is a big factor.
I can’t speak of specific US building codes, but here in Canada, yes all building codes would apply, and to some degree are even more strict on exterior stairs simply due to the fact the general public may have access to them (the mailman the neighbors kids etc.)

-- “Wise men speak because they have something to say; fools because they have to say something.” – Plato

View WyattCo's profile


93 posts in 712 days

#9 posted 03-27-2018 07:03 PM

Use 2×16’s for all three stringers. No center support(s) needed. No “bounce” either.

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