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-   -   Joist span no longer adequate, how to upgrade (http://www.diychatroom.com/f19/joist-span-no-longer-adequate-how-upgrade-171645/)

Wellc 02-11-2013 06:31 AM

Joist span no longer adequate, how to upgrade
 
Renovating a one story house with an open attic space with hardwood floors, to me it would make a large bedroom. After taking the drywall ceiling down on the 1st floor we exposed 2x6 ceiling joist 16" on center spanning 13' 0", my carpenter friend helping me replace the ceiling said the area above was designed for storage & not living space, he's suggesting 2"x10" joist, 2"x8" were borderline. I didn't want to tear up the floor in the attic so is there other options? Maybe sistering additional 2"x6" to existing or adding plywood between the sistered joist.

Thanks for any help

AllanJ 02-11-2013 07:38 AM

I am thinking that sistering every one of the joists (or adding more 2x6 joists to have them on 8 inch centers) would work fine. But you should run it by a structural engineer.

If that doesn't work then maybe 2x8 joists sistered to the existing 2x6 joists (which remain in place) will do.

Again, run it by a structural engineer but, if you do it with sistering, generally the new joists do not have to go all the way to the rim joists, which would make it easier to install them.

Alan 02-11-2013 09:18 AM

Quote:

Originally Posted by Wellc (Post 1114731)
Renovating a one story house with an open attic space with hardwood floors, to me it would make a large bedroom. After taking the drywall ceiling down on the 1st floor we exposed 2x6 ceiling joist 16" on center spanning 13' 0", my carpenter friend helping me replace the ceiling said the area above was designed for storage & not living space, he's suggesting 2"x10" joist, 2"x8" were borderline. I didn't want to tear up the floor in the attic so is there other options? Maybe sistering additional 2"x6" to existing or adding plywood between the sistered joist.

Thanks for any help

There's an episode of Holmes on homes where someone did this and tried to shortcut it. They ended up having to rip most everything out that was already done. Look it up on youtube maybe.

I agree with the structural engineer comment.

md2lgyk 02-11-2013 11:11 AM

My wife designed our house, and the log home company drew up the blueprints. The joists are 2x10s. But in one area of the house, the span is about 3 inches longer than the IBC tables allow. What the log home company's architect did was specify the joists at 12" oc in that area, plus double joists in the areas of high traffic. Trust me, my kitchen floor doesn't bounce or sqeak.

I don't know which would be harder, sistering the existing joists or adding joists in between, but I'm pretty sure either would be acceptable. But, then, I'm not a structural engineer. I think to be absolutely certain, you should check with one. Unless you live in one of the few places with no codes, you're going to have to submit plans with the permit application anyway.

tony.g 02-11-2013 12:17 PM

Timber floor joists are normally checked for 1. bendng stress and 2. deflection (sag).
In domestic loadings, deflection is usually the critical factor.
Assumung your live load is 40psf and dead load 10psf then that would give a maximum loading of 864 lbs per joist. If the joists were sistered to give 2 1.5 x 5.5 joists fixed together, your maximom deflection would be about 1" (assuming a medium-strength softwood). This would probably NOT comply with the deflection limit which might be specified in your code. You would be better off sistering them with 2x8s, though as the other guy said you don't have to take them end-to-end.


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