Problem: deck surrounding an above-ground pool
(deck standing on wood posts into sand without
appropriate foundations) has sunk badly at one
corner, has sunk 9 inches at the pool edge, and
17 inches at the outermost corner. Thus the corner
post has sunk about 17 inches and two or more
intermediate posts about half that.

(This deck & pool are about 19 years old and
I contemplate repacing both whenever the
pool collapses . . . I.e. repairs should last two
or three years.)

I plan to raise the deck and support it by
a new joist of doubled 2x6" cedar (i.e. 4x6" total)
diagonally under the corner, and supported at each
end by new posts (4x4" lumber) on 2ft concrete slabs
atop the ground (sandy soil). The deck must first be
raised by one or two auto jacks, placed atop 12" drums
cut from a large poplar tree (2 ft. diameter.)

Questions remain:
1. Should I raise the deck with a single jack
under the deck (lifting the new diagonal joist)
or a pair of jacks outside the deck footprint?
This would require having the diagonal joist
extend at least 3 ft. beyond the deck footprint
at both ends (and cutting off the surplus when
the job was finished.)

2. How fast should I try to raise the deck?
I.e. if it seems to stick at (say) 3 inches, should
I just leave it overnight and try to raise it another
3 inches next day? Or should I use two jacks,
crank one end up 3 inches, then raise the other
end 3 inches, and repeat at the first end?

3. Two new pillars (resting on concrete slabs
on the ground) will be hangered to the new
2x2x6 diagonal joist, the pillars placed under
the edge of the deck like the others. But just
how far from the corner post should I fit this
diagonal, e.g. 2 or 3 or 4 ft. from the corner?

4. If I can raise the deck and insert new
supporting posts as planned, would there be
any point in digging below the old corner post,
with a view to filling the empty hole below it
(probably 17 inches deep)?

--
Don Phillipson
Carlsbad Springs
(Ottawa, Canada)