Floor joist cross bracing

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Old 02-25-15, 06:08 AM
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Floor joist cross bracing

Hey guys, I have a finished basement that I am getting ready to install ductwork in for my house. I don't have any room to lower the ceiling anymore so that is not an option. Where I want to run the round pipe through the floor joist there is approximately one cross brace in the way for each supply I am running to the room. I would need to remove a total of 3 cross braces out of different ares of the floor. From my understanding, they are just for keeping the joist more square and helping reduce sagging and squeaking. Is it going to hurt to relocate or remove said cross braces to allow my ductwork to fit through?
 
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Old 02-25-15, 06:28 AM
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It is normal to forego cross bracing whereever the ductwork has to run.
 
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Old 02-25-15, 06:35 AM
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Better to do that than to cut joists or I-joists. I have seen it done in new construction, and cringed at the outcome later down the road.
 
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Old 02-25-15, 06:36 AM
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So it shouldn't be a problem removing a few?
 
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Old 02-25-15, 06:38 AM
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What type of flooring is located in the room(s) above? If tile, it may be of concern. The closer to an outer wall if running parallel to the joists would have the least impact. Cross bracing ties joists together so that the weight placed on one is distributed over 3 joists. I have remodeled where the only way to stop movement was to add cross bracing.
 
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Old 02-25-15, 06:40 AM
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Not going to hurt a thing.
 
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Old 02-25-15, 07:24 AM
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Its hardwood flooring above it.
 
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Old 02-25-15, 03:27 PM
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What size joists vs what size duct work. Is the hardwood above full nail down solid 3/4" planks? What is the length and width of the room? What age of the house and is the floor original? Should be OK but just looking for the missing pieces of the puzzle.
 
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Old 02-26-15, 05:33 AM
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Floor joists are 2x10s, the floor appears to be fullly nailed down, solid 3/4 planks. One bedroom is 12x10, the other 10x10, I've decided to use oval duct to go underneath the cross bracing that would be dead center of the living room. House is 1959, original floors.

Duct work is mostly 8" round, but going to get some oval.
 
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Old 02-26-15, 06:11 AM
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Have you considered flex? Otherwise, don't fret over removing a few cross braces to accommodate the duct work.
 
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Old 02-26-15, 06:16 AM
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Sound like a good plan. Some homes of that vintage only used 1/2" plywood underneath the hardwood. Today, the industry minimum standard is 5/8" for plywood and 3/4" for OSB. Your joist spans are well within specs provided you are at least #2 grade or better.
 
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Old 03-01-15, 12:23 AM
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Be careful cutting big chunks out of your joists...

And why not just cut out holes in the cross supports? (oops, I was thinking about "solid blocking" from here; http://www.doityourself.com/stry/flo...ross-bracing#b)

Ideally they are solid 2x at the same height as your joists. All that matters is support at the top and bottom, so a big hole in the middle isn't a big deal. And it'll hold your ductwork up, too

But what's a bigger deal is if you're cutting big holes through your joists without reinforcing them.

Sounds like a job for a structural engineer.

If you do any bracing without talking to an engineer, here's the short version of what my engineer did for me (I was notching the bottom of a 2x12, though). 2x6s along the top of each 2x12, but he was VERY insistent to use doug fir #2 or better wood AND to use 16 penny common (common is very important) nails (holy cow they're big) and a LOT of them - a row along the top of the 2x6 at 6" spacing and a row along the bottom, staggered at 6" spacing. It's very important to be able to transfer the load to the bracing (lots of very thick nails) and for the bracing to be able to withstand that shape of torque (the requirement for the variety and quality of wood).

tl;dr: don't cut holes in your joists and reinforce with crappy wood and flimsy nails.
 
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Old 03-01-15, 05:35 AM
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Thanks xaxxon - But the OP was talking about cross braces running parallel to the joists.

remove a total of 3 cross braces
Nothing was mentioned about having to run duct work perpendicular through the joists or anything about solid braces. He is not jeopardizing the integrity of the floor system which differs from your situation.
 
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Old 03-03-15, 07:34 AM
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Thanks for the great advice guys. I found out even with using oval duct I still need to remove some cross bracing due to the 90 degree boot will cause the duct to need to connect about 2.5" below ceiling. I will need to remove 1 set of braces near where the boot will be. I will fix this by blocking both above and below the duct with a 2x4 to make up for the removed cross brace. I would rather keep the duct as close to the ceiling as possible to stay out of the way of wires and such, so this is the best route.
 
 

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