Timber Framers Guild

minimum drop in joist pocket size

Posted By: 51steve

minimum drop in joist pocket size - 04/12/20 05:18 PM

Hello Everyone,

I am in the design stage of installing 10 foot long 5x7 white oak drop-in floor joists on a preexisting 11 foot long 10x11 white oak summer beam and I was wondering if there was a minimum drop in joist pocket depth? Looking at the "floor joist sizing rule of thumb" the depth should be less than or equal to 5/8ths of the width of the beam. Based on the spacing of the joists(31 inches on center) and the load each pocket will need to bear 715 lbs. I would prefer to make the smallest pocket possible because 1) I dont want to weaken the summer beam. 2) It's oak that's been drying for 10 years! I will be scoop cutting the floor joists down to 5 1/4 so my pocket dimensions will be 5 x 5-1/4 x depth... that's what I need help on! There will be 5 3/4 of wood underneath the joist pocket.

Thanks in advance!

Steve
Posted By: Jay White Cloud

Re: minimum drop in joist pocket size - 04/12/20 09:11 PM

Hello Steve,

There is, as you suggested many old "rules of thumb" for such applicaiton. Another is "2 and 3...3 and 4" which translates into the distance in inches between joist pockets on the top of a Summer beam and the distance from of the pocket on the bottom...min and max.

I'm found of soffit and/or tusk tenon for such applications, not dovetails...even if the tenon has to be "free" and slid in.

Your timber sizes seem more than adequate if I'm understanding the overall design without seeing a CAD or drawing, so no issue there.

Your reduction of the joist (aka scoop cutting) seems acceptable but not necessary at all, and would only be dependant on aesthetic you are trying to achieve. A fully house joist appears achievable if it is desirable...

As to the "smallest pocket possible" that motivation for strength maintenance is not really a concern it would seem? As to cutting the pocket, a "v" gouge (aka corner chisel) and a #5 in or out cannel gouge would make short work of this task in either green or dry oak without much effort. Then simple cleanup with slick or paring chisels...Of course any applied power tools and/or saws can be employed according to skill set, tooling and applied knowledge to effectively use them of course is also part of the tooling should you have these?

Hope that was of some use...

Regards,
j

Posted By: Will B

Re: minimum drop in joist pocket size - 04/13/20 01:03 PM

1"
Posted By: 51steve

Re: minimum drop in joist pocket size - 04/14/20 12:58 PM

Thanks for the quick replies and helping me through this process! I have been scoop cutting a few trial joists on scrap pieces with fair results and hope to cut some sample pockets soon before heading on to the "real thing".

Thanks again!

Steve
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