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Question I have has to do with my joists. The builder put smaller pieces of joists perpendicular to the long joist spans. These seem to be near the corners of the house and run for about two sections of joists. Wondering 1) why, and 2) if I can cut out some of the small piece joists to run 6" duct.

They look something like if you could look at them from the top:

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Thanks
 

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The short pieces of wood are called blocking. The keep the joists from twisting along the span. They are usually placed in every joist bay every 1/3 of the way.
Fell free to remove a few here and there to run mechanicals. If you can replace them in another spot, out of the way, it can't hurt.
Ron
 

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someone else will be able to give you more technical and thorough answer but I believe they are just an extra form of support to keep the joists straight. I can tell you that in my house several have been removed or cut when they put my hvac in. Again dont take my word as gospel. Someone else will give you a better answer.
 

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Although you won't have the same strength to avoid twisting it's not a bad idea to replace the spacer once the 6" pipe is in with the same peice turned flat ....and brace the sopce either side of the joist space you are working in
 

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Generally, they are installed in the last two bays closest to the outside walls, for floor shear. The joists with a rim have shear flow, but the joists running on the ends do not. Many engineers add the blocking, 2' on center, with special nailing. Unless they are installed that close, they wouldn't do much. Be safe, G
 

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Although you won't have the same strength to avoid twisting it's not a bad idea to replace the spacer once the 6" pipe is in with the same peice turned flat ....and brace the sopce either side of the joist space you are working in

this is what my HVAC guys did actually.
 

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I tend to agree with GBar but am puzzled. These are not your typical floor blocking because they would be located out further away from the wall (8-10 feet) and in every bay. Instead they may well be intended to resist the soil pressure against the foundation walls. But if so, I would have expected more of them and the corners would be the least likely area to put them if trying to get by with fewer.

Can you get hold of the builder or maybe the local building inspector to find out what the purpose of the blocks is? It's always good to know exactly what somethings function is before you mess with it.
 

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1. Are the blocks 4' from the corner of the house?
2. Is there a solid, no windows, wall above?
3. Can you see any hardware at the 4' studs? Maybe a bump in the outside ply or siding, showing a strap or hold-down attached there?

Joist blocking for lateral displacement (roll-over) is only required on 2x12's and bigger, every 8' - across the whole span. IRC 502.7.1 UBC 2316.2 So it's not for this.

I think it is for the shear walls above, to transfer the wind and earthquake loads to the floor, on into the foundation. Which would explain the corners only as that is required by codes. Try to leave the top 1/3 of the blocks intact, as this is where the deck nails are. Be safe, G
 
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