Running a 3/4 ledger under the bench is a fine idea. No problem with
strength as you describe. Personally I would use small lag bolts into
the studs maybe 5/16" or 3/8". Screw pull-out would be your only
concern here so the lags give more bite. The deck screws won't likely
pull out but a commercial grade approach would use lags.

As far as attachment up to the bench, I would probably use table irons
or other typical attachments like used for a table top. Across the 18"
width you will get some expansion and need to account for that in a
sliding attachment. Plus is seems difficult to screw up through a 3/4
wide board and that puts your screw at the very end and edge of the
bench slab.

You could use pocket screws but that puts the screws even farther
toward the end and edge.

Finally, you only need a little grab into the bench top, just enough
to keep it from sliding or coming loose. Also, I don't think this
would ever sag and in fact I would probably just put a ledger at each
end but having it along the back will make it a littloe more stable.

On Jan 17, 7:20*am, blueman wrote:
I am building a 52" x 18" x 2" (actual dimensions) white oak bench for
a small alcove that is surrounded on 3 sides by walls.

To support the bench, I am thinking of using white oak cleats along the 3
supporting sides and screwing up through the cleats into the bench so
that there are no (obviousy) visible fasteners

Would a running 3/4" x 2" cleat along 3 sides of the bench be
sufficient to support the bench under easonable use? (say maximum of
3 adults or 4 children sitting on it).

Assume that the cleats will be screwed into the studs every 16 inches
using a 3 1/2" deck screw. Assume also that 3" deck screws will be
used to screw up through the cleat into the bench.

Thanks