# re: joist blocking/strapping alternative



## gramps416 (Dec 26, 2008)

*re: joist blocking/strapping alternative*

I am interested in running some new ducts between my joists. It is an old home using 2"x8" 12" o/c, giving very little room inside for the ducts.

Currently, the cross-bridging method (see picture) is used for blocking.
I was wondering, if in one bay, i can remove the cross bridge and insert one 2x4 or 2x3 block on the top and on the bottom, spaced 1 foot apart (see diagram with red markups).
Using that method, there is enough room to fit my duct.

Would this work, and be safe as an alternative method? i may have to use sub-floor adhesive in addition to fasteners. 
thanks
-g


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## Daniel Holzman (Mar 10, 2009)

Blocking provides a few functions. It effectively eliminates the chance for horizontal buckling of the joists (that is rare anyway). It ties adjacent joists together, which reduces the potential for creaking of the floor when you walk on it. There are lots of older houses built with minimal or even no cross bridging, and they survive just fine because the bridging provides no bending strength. As for your plan, it seems pretty reasonable to me, as you will provide effectively the same bridging as before.


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## gramps416 (Dec 26, 2008)

Daniel Holzman said:


> Blocking provides a few functions. It effectively eliminates the chance for horizontal buckling of the joists (that is rare anyway). It ties adjacent joists together, which reduces the potential for creaking of the floor when you walk on it. There are lots of older houses built with minimal or even no cross bridging, and they survive just fine because the bridging provides no bending strength. As for your plan, it seems pretty reasonable to me, as you will provide effectively the same bridging as before.


except that there is not cross bridging (expansion control), but does that really matter anyways?


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## ron45 (Feb 25, 2014)

Turn them to represent solid blocking....


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## gramps416 (Dec 26, 2008)

ron45 said:


> Turn them to represent solid blocking....


I can't turn them, the point of this plan is to attempt to give myself as much spaces as possible to run the largest diameter ducts that i can fit


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## ron45 (Feb 25, 2014)

I don't see a problem as long as it's only one bay, not two together.
You could use 1 by's or even 3/4" real plywood and attach with pocket hole joinery. I take it you don't want to use the strapping method.?
Still, I would test the floor before installing the ducts. I say this because you didn't give the length of the unsupported 2x8 , 12" OC., or what's above.
Here's a good start for that.
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp

..


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