Supporting deck stairs

Old 03-30-09, 07:48 AM
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Supporting deck stairs

I have a deck made out of composite materials (ChoiceDek from Lowes) that has 8 steps going from the deck to the ground.

The stairs are 48" wide, and so for added support I have a 3rd stringer in the middle.

But I'm still concerned that it's not enough. I read after the fact (I know, I know...) that ChoiceDek recommends a stringer every 12 inches!

I had a recommendation from a contractor that I could nail 2x4 underneath the stair boards (nailed on both sides into the stringers), but I don't know if that's worth doing.

I'm trying to avoid having to build 2 more stringers and put them on to my (already assembled) stairs, but I will do it if it's the best (only?) way to prevent long-term sag
Old 03-30-09, 01:56 PM
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Hi, regoarrarr. Yes, you need them 12" o.c. I would sister a treated 2x4 to each as well. If they are being inspected - - open risers no opening >4" except tread/riser triangle 6" max. Grippable handrail required, 34-38" up, sorry I got carried away. The 2x4 voids the warranty, doesn't it? Paper trail your warranty. Be safe, GBR
Old 03-31-09, 05:22 AM
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It seems to me the stringer spacing should be the same as the joist spacing used when the deck was built.
Old 03-31-09, 07:09 AM
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I'm shooting in the dark here so use this if it has any value. I didn't see backers included in your post, but backers can support the heel of one step and the toe of another, creating a box structure that should give you some additional support. Not sure how you fit them in, but may be an option.

Old 03-31-09, 04:09 PM
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With your steps being 4' wide, you need to support those treads every foot, so that they are anchored in 5 spots across that 4' width. Otherwise they will flex and be 'springy', or at least have enough flex that it will start working on the points where they are anchored. Removing the boards and building a 2X6 box between the existing stringers will work, but add a 2X6 at the center of each of those 2 boxes that is parallel to the stringes so that you gain an additional anchoring point for the deck boards.

Wirepuller -- it's all about the number of anchoring points for each board involved, not just the span. Composite deck boards come in 12', 16' and 20' lengths. The shortest, with the joists at 16" OC, is anchored in 10 spots. I WILL NOT let my crew install a composite deck that is anchored in less than 5 spots over it's length.

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