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I want to set up some weight lifting equipment in a room on the first floor of my house. There is an unfinished basement below. (Big disclaimer: I am not going to use the results of this calculation to determine if my plans are safe. This is for my own understanding only. The possibility of "second order incompetence / not knowing enough to know what I don't know" is too high for something like this, so I am hiring a structural engineer to make the actual "safe/not safe" determination. If unsafe, hopefully said engineer can tell me how to make it safe.)

I am trying to calculate the safe live load for this floor. My actual questions:

(a) Have I done something totally wrong below in my look ups or logic?

(b) When measuring the span of the joists - do I measure the full length of the board, or the length of the board not directly supported by the wall or metal I-beam?


The joists are 2x8s, spaced every 16 inches (e.g. there are 14 inches between joists). They span roughly 14 feet. I was able to find only one stamp:

enter image description here

If I understand correctly, that's grade 1 of spruce, pine, or fir. This is listed on page 17 of the design values table (pasted below). For safeties sake, I am assuming it's "Spruce-Pine-Fir (South)" since that seems to be slightly weaker than the other option:

enter image description here

Also for the sake of safety, I will assume it's a mix of grade 1 and grade 2 lumber (have only found this single stamp so far). That means Fb = 1070 and E = 1,100,000.

Hopping over to the span tables.. it seems like I am in trouble, because this floor can't even support a 30 PSF live load:

enter image description here

Okay, that's a little scary, maybe my assumptions about type of lumber (SPF, instead of SPF-Southern) and grade (all grade 1, instead of mixed 1 and 2) were incorrect. That leads to Fb = 1,210 and E = 1,400,000 - which might just support 30 PSF.

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  • Hmm, weren't there some comments here?
    – negacao
    Jun 6 '21 at 0:43
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The approach is fine for the purpose of existing joist capacity evaluation, however, note that in the deflection table, the limiting span length is derived by imposing a live load of 30 psf (see criteria), which is less than the 40 psf usually specified by the building code. To be correct, you have to confirm which live load value was in effect at the time of design. You may need to find the table corresponding to 40 psf live load.

Other notes:

  • For the bending and reaction table, you have to make sure the unit floor load back-calculated using the listed values exceeds the combined live load and dead load.

  • In determining joist capacity for the new loadings: For bending, you need to check the effect of concentrated loads from the equipment and the effect of potential dynamic/impact load induced by the user(s). For deflection, you need to use the proper equations and parameters to perform the calculation, which will not be available by any table.

I agree with Solar Mike's comment to have an engineer look into it for safety.

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  • Thank you. :) I do think code requires 40 psf live load here - we'll see what the engineer says, this could end up being kind of obnoxious.
    – negacao
    Jun 5 '21 at 20:27
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The other answer is the craziest answer I can think of. Why give an answer that says: “gee…you should check what the code requires” ?

First, 2x8’ at 16” on center with a span of 14’ can support a “Total Load” of 68 psf.

Second, the “Dead Load” is probably about 2.5 psf for gypsum board ceiling, plus 2 psf for the 2x8 joists at 16” on center, plus 3 psf for plywood subfloor and plywood underlayment, plus 2.5 psf for carpet or wood flooring, for a total “Dead Load” of 10 psf.

Third, this leaves a total available “Live Load of 68 psf - 10 psf = 58 psf depending on the exact species and grade.

Fourth, this Live Load is assumed to be distributed across the entire area. If your room has a couch, tables, chairs, etc. and you’ll have 10 people in the room, then “No” it probably won’t support your added load of weights.

However, if the room is 14’ x 10’ and no furniture or visitors, then it will support 14’ x 10’ x 58 psf for a total 8,120 lbs. So, now you can answer the question yourself. If you have 3 - 200 lbs. friends for a load of 600 lbs. then your weights should not be more than 7,000 - 7,500 lbs…just to be safe.

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