Foundation for steps

R0X

I'm cutting 3 stringers for steps leading from my new 4-seasons room to my concrete patio. The patio is a kidney shape, and due to the curved edge I found that 2 stringers will sit fully on it, but the 3rd barely touches it. (see pics attached) I'm looking for options for the 3rd stringer's foundation which avoid pouring concrete. Any ideas would be greatly appreciated.
Thanks

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tony.g

Can you make the staircase longer, ie 3 risers but longer treads; another couple of inches on each tread would give you a good bearing.
Or is space restricted, or does your Code stipulate a specific relationship between rise and tread?

R0X

Space is kinda resticted on the patio, plus the total height is only 22" so more/bigger steps might look weird. I was wondering if I tied the bases of the 3 stringers together and if 2 were fully on the concrete, whether the 3rd one could be partly on the concrete and just have aggregate underneath the rest. Then again, the inspectors might not like that idea...

KevinPh

In most situations, stringers should not be placed on a patio or walkway, but should have their own foundation - usually compacted aggregate is fine for 22" steps. If you are in a location subject to freeze and thaw cycles, putting the stringers on the concrete patio will cause the patio to crack over time.

If it was me, I would cut out the area of the concrete patio where the stringers go, and build a proper foundation (compacted aggregate) for all 3 stringers. The structural integrity of the stringers and the patio will then be sound.

jcarlilesiu

I think this is being way over thought. Your concrete probably has between a 3000 - 4500 PSI bearing strength. Considering the width of the 2x, and the expected loading on the stairs, I think you are comfortably within range.

Additionally, simply closing off the first riser with a 2x will help spread the load back to the stringers which have more bearing on the concrete. Infact, it should spread the load across the front evenly if the closed riser is touching the concrete as well.

R0X

Yes, I'm trying to keep it as simple as possible. I like the idea of closing off the first riser with a 2x to link all 3 stringer bases together. I'm also going to increase the step run from 10" to 12", which will increase the total run by 6" to allow about 2/3 base of last stringer to sit on the patio.

Anchoring to patio: I was thinking of adding a flat 2x between stringer bases, and anchoring it to patio with concrete nails. Do you think this would be sufficient?

hammerlane

Yeah right!!

jcarlilesiu

Here is the problem. In reality, your wood stringers should have terminated above the patio level. The reason being, is that its easier to provide a concrete surface which sheds water away if it was an independent structure than the flat slab. (Such as a concrete pier)

At this point, I wouldn't go back and put a pier under the stairs since its such a small load. Be sure however that the concrete doesn't pond under the wood stringers, if it does I would suggest a shim that will hold up to continual contact with water.

I wouldn't use 2X between the stringers as we want to try and minimize the amount of contact the wood has with the concrete.

I would actually use something like this on either side of the stringers.

http://www.shortrunpro.com/thick_gal..._vhv20ytw.aspx

Or

http://www.shortrunpro.com/deck_rail..._vhv20ytw.aspx

(Not sure about those prices, I think this is a bulk order site, but you should be able to find this at your local hardware/improvement store.

Additionally, I would leave about a 1/4" space between the bottom of the wood and the patio.

rjniles

I would put a piece of heavy aluminum angle under the floater. Might do for all 3 to prevent the direct wood to concrete contact.

__________________
Location:
Coastal South Carolina

R0X

Yeh, that makes sense. So how would you anchor it to the patio?

jcarlilesiu

Its concrete right?

Tapcons would be fine. Loading from the stairs is mostly vertical, thus the screws into the concrete will simply resist lateral racking. Not much load in that direction.

For the clip angles, try to find them in S.S. or aluminum, if you can't then make sure they are galvanized.

concretemasonry

R0X -

I don't know your location, but just keep in mind that your patio will move in relationship to your home during the winter in many areas. If the patio heaves and the steps are anchored the anchors could be ruined or the moving stairs may be ripped off the house attachment.

Dick