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Discussion Starter · #1 ·
Hi guys,

To introduce myself I have been in business for 10 years doing bathroom and kitchen remodeling. On this particular project in question I am adding an addition on my own house and would like some feedback on the joist sizing.

I am doing a low pitch 1/12 , rubber roof. In order to maximize the height in the room I need to use 2 by 10 joists maximum. (2by 12's i lose 2 extra important inches). The clear span of the joists is 13 feet, 10". I will be spraying foam under the roof deck sheathing. I need to space my joists 24"O.C. (It is too involved to explain why 16" OC will not work).

From the load span tables (Number 1 southern pine, 2 by 10, l/360 deflection, 40 psf live load, 24"oc I know that the maximum allowable span is 14'7". Again my span is 13'10".

My question is.... Is this too close to maximum span? I live in southern ohio and we do not get tons of snow, 23" per year maybe. I tend to error a little on the conservative side as a general rule (slightly overbuilding).

One thought is that every third joist I would double up and bolt them together.

I do not want sagging problems over time (30 years, and beyond).

However, maybe I am being a bit too cautious or over-concerned. Will you advise just to do the 24 oc spacing (not doubling up on every third or every other... and be done with it?

Additionally, I was planning on 5/8 osb (remember 24"oc) - will this be strong enough? Go to 5/8 ply? 3/4 osb? 3/4 ply. Again, I want long term durability, but not to OVERSPEND(wasting money where it is not necessary). Thanks...


The Duke
14,746 Posts
Hard to say 100% since I feel you have some other necessary details missing from your post. I'd definitely go with 3/4 for 24" oc. 5/8" should be ok but not for my house. Get it dry quickly.

Are you going to rip the taper into the joists? That comes into play some also when figuring.

You said I joists in your title but talk about 2x's in your post. 2 different beasts.
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