Reply by clin

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Posted on What screws to use for floating vanity frame?

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1128 posts in 2080 days

#1 posted 12-09-2017 07:44 PM

Since it is supported on three sides, the loads are pretty small at any point. Your worst case load is the 300 lb guy that will sit on it.

The cleat that jerry shows is the way to go. You don’t need a 2×4 frame up against the wall. 1×2 would be enough. The front end, of the two side cleats, are where the greatest load will be and two screws there is not a bad idea. Though one good size screw like a #14 should be plenty.

Elsewhere, one in each stud is certainly enough. As for screw length, you will probably have 1/2” drywall and then the thickness of the frame/cleat.

Assuming a 1” thick frame/cleat, + 1/2” drywall, + 1” screw into stud, as TheFridge suggested, you need screws 2.5” long. If you use 2×4 or similar frame/cleat, then you need another 1/2” so 3” long. A bit longer doesn’t hurt, but unless you know for sure there isn’t wiring running through the studs, you don’t want to just run 2” deep into the stud.

#8 screws are probably plenty big, for all but the front end of the frame. You won’t break (shear off) the #8, but they could bend. The bigger the screw, the less they will bend and the more wood the forces are spread over. So maybe just go with #14 or similar fro those front ones. You’ll want to pre-drill for those to make sure you don’t split the frame/cleat or stud. I’d pre-drill the frame/cleat no matter what, makes it easier to pre-load the screws when mounting. For #8 screws in the stud, you don’t need to drill the stud.

You didn’t describe how the shelf was constructed. At 50” long, you will need some strength along that front edge. If the top is something like 1.5” hardwood, then that’s likely plenty. But if the top is laminate covered particle board or similar, then you need to support that.

This of course may be why you have described a frame. And certainly a 2×4 frame going around all 4 sides is more than enough. Smaller would still be okay, even for the 300 lb guy who will sit on it. You just want the shelf to not bend too much under an extreme load. And of course not bend or sag at all under it’s own weight and the weight of the sink.

Often a smaller frame is desired for looks. If so, you could consider a steel tube long the front.

-- Clin

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