Are My 24" Oc Trusses All The Floor I Need? - Building & Construction - DIY Chatroom Home Improvement Forum

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Old 09-13-2007, 12:57 PM   #1
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Are my 24" oc trusses all the floor I need?

Looking at Gambrel trusses that are spaced 24" on center. The lowest horizontal member is the floor joist also.
Is it right that the floor joists would then be 24' oc because that is how the trusses are mounted? OR do you supplement in between the truss joists with other joist material?
If it is 24" oc, what flooring gives you solid feel? 3/4 ply t&g?


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Old 09-13-2007, 01:32 PM   #2
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The truss manufacturer would be able to tell you if the truss is designed for use as a floor and what the load rating is. Your local building dept can tell you if that rating is acceptable for the rooms purpose. For example here a 40 psf live load and 10 psf dead load is required for all rooms (except bedrooms allow a 30 psf live load rating).

Plywood typically is identified with the acceptable floor joist spacing right on the panel - or you can call the manufacturer. It also will have the rating for use as roof sheathing so don't confuse the two. The floor joist rating is the second, smaller number. For example, it will say "32/16" if it's rated for 32" oc rafters when used as roof sheathing and 16" oc floor joists when used as subfloor.

So if the truss is rated for your purpose then for floor then select a plywood subfloor that has a 24" oc floor joist rating. I don't know if a 3/4" plwood T&G subfloor is rated for 24" oc but even if it is I'm betting that a 1 1/8" subfloor would feel a lot better. Be sure to use T&G material as subfloor with all butt ends ending on the joists.

You probably won't need additional floor framing besides the trusses but ask the truss manufacturer.


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Old 09-13-2007, 02:14 PM   #3
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new here and thankful for response

Thanks! Great I response, I learned even more. I'm new to this and very appreciative.
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Old 09-13-2007, 04:20 PM   #4
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Also for "storage" only 10 or 15psf may be allotted for in the design. If you dont specify they do this to keep the quote down. For an attic this might be ok, for living space it varies by local codes as stated. Also even if its non living space you can over rate like my garage i calculated it for 40psf so I can store lots of engine and car parts up there.

Regardless of the design with 24" oc you will get some bounce just from the flooring material. Two ways to help this. Use Advantech T&G instead of regular OSB T&G... both 3/4 both glued and screwed the Advantech is about 40% stiffer, I have written other threads about this so I wont go on. The other thing Ive done prior to Advantech being on the market is add another layer of subflooring. I used 1/2" cdx with constr adhesive. I staggered the joints and ran it the opposite direction. I used Long screws through both over joists and short elsewhere when needed. This made for a nice bonus room over the garage. My teenage daughter has had at least 20 friends in there running around dancing and having pillow fights no problems. Ive even put tile over this succesfully but that was elsewhere and at 16 oc.
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