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Fasten Joist to Subfloor From Below

IVDan's picture

Are there any suitable techniques for fastening joists to subfloor from below?

I am installing new floor joists in my second floor from underneath by opening up the first floor ceiling.  I'd really rather not have to tear up the floor on the second floor to fasten the subfloor to the new joists, so am looking for a way to fasten from underneath.

Thanks for any input you can provide.

I once used some aluminum (post #216614, reply #1 of 5)

I once used some aluminum brackets that were sold for this use.  They were a chunk of aluminum with holes drilled for screws into the joist and subfloor.  (A "chunk" so they were much stiffer than ordinary bent steel corner brackets.)

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Interesting Idea (post #216614, reply #2 of 5)

Thank you - that seems like a reasonable approach.

IV (post #216614, reply #5 of 5)

In either of the above and in addition PL Premium adhesive you can toe screw thru the new joist into the subfloor if it’s thickness will allow.  If there’s some sort of good finish above, you'd best be very carefull screwing around...

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


Hi there, what is the purpose (post #216614, reply #3 of 5)

Hi there, what is the purpose for installing the new joists? Are you leaving the existing and sistering the new ones?  If so, then construction adhesive between the old and new and on top of the new joist is the way to go before mechanically fastening the new and the old with structural screws.  Best of luck

A bead of polyurethane foam (post #216614, reply #4 of 5)

A bead of polyurethane foam will do nicely.

Florida Licensed Building Contractor, 50 years experience in commercial remodeling, new homes, home remodeling and repairs and all types building maintenance.