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I want to span a 76" gap. People won't walk on it, but I want to make sure it could support an adult.

What is the minimum size I should use?

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Suggested Edit:

This is to hold a decorative item. It is not a walkway. However, an adult would stand on it for about an hour to work on the decorative item.

3 joists, spaced evenly over 2'.

Attached to both end of the walls by [ to be determined].

Here is a rough mock up...

rough

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    A regular two-by-four could support an adult at that span. For how long, you ask? Well, you didn't ask so take it for what it's worth.
    – MonkeyZeus
    Nov 17, 2022 at 14:34
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    Websearch "sagulator"
    – keshlam
    Nov 17, 2022 at 15:04
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    For safe floors you usually can start with an inch per foot of span, so at least 2x6 joists. Smaller dimensional wood will be in the 'Might hold' instead of will hold range.
    – crip659
    Nov 17, 2022 at 15:41
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    Are you asking about laying the wood flat (long dimension side-to-side) or are you asking about standing up (long dimension up and down) like a floor joist?
    – RetiredATC
    Nov 17, 2022 at 18:07
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    Your question leaves a lot of gaps. What's the purpose? What joist interval do you plan? How will they be anchored at the ends? (There's a substantial cantilever effect if they're fastened at the outside of your diagram.) Please revise to be more clear.
    – isherwood
    Nov 17, 2022 at 19:38

1 Answer 1

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My staging planks are 71-3/4" 2x8, with the occasional 2x6, and I would expect them to be fine for another 4" span, but you could crank up to 2x10 or 2x12 if you like. The 2x6 are noticeably more springy than the 2x8, for a point of reference.

I would not use 2x4 on the flat without something to spread the load to more than one 2x4 - that's begging for trouble.

Depending on duration, price of materials, and what you could reuse the materials for after this (presumably temporary) thing is done, a sheet of OSB or plywood with a few vertically-oriented 2x6 screwed under it might do the job more efficiently.

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