Lifting sagging deck

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
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 12 Apr 2006 10:53:41 -0400, "Don Phillipson"

If the deck is sagging because the supports are sinking, why do you want to mess with adding beams and other posts?
Just dig out around the sinking posts, jack them back up, and pour a bigger footing under them. Failing that, for a 3-year repair, you could probably get away with just jacking the corner up, and bolting a pair of 4' cross-peices to the post, at ground level, as an extra bearing surface.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ask your doctor about Levitra.
Oh, *DECK*
Carry on.
-- Todd H. http://www.toddh.net /
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 12 Apr 2006 10:53:41 -0400, "Don Phillipson"

Why not a single jack outside, or a pair inside? That is, I don't understand why these are the two choices. Oh I get it, now.
I've done this but on a much smaller scale, a 6 foot by 12 foot deck that had only sunk 8 to 10 inches.
I used a floor jack and I thought it worked great. That's the one that looks like an lizard, with a lever one end, a platform that goes up on the other end, and 4 wheels on the part in the middle. I put the "platform" just aabout 6 inches to the side of the post that had rotted away. (26 year old deck) That way there was room to put in another post beside the first post. I plan to enlarge and replace the thing this summer.

Like I say, my plan worked fine. I jacked up one side and put another piece of 4x4 in to hold it up. Then went to the other side 12 feet away, and jacked that up.

I don't think it will stick and i don't think waiting overnight will change much. Why do you think it will stick?

Despite the fact that the other edge of the deck stayed attached to the house, and the near eadge was only 6, or 5, feet from the house, each corner seemed not to care what the other corner was doing. Lifting up one corner didn't make the other one, 12 feet away, move at all. But I only went up 8 to 10 inces.

How deep is the whole hole. That is how much above the soon to be empty part. I don't think it would take much effort to open a channel from the side of the post to the hole and fill it with rocks, stones, soil, more rocks, stone, soil. Or something more permanent, if permanence isn't a problem. Then there would be that much more for the deck to rest on. (although the horizontal beam at ground level someone else suggested would solve that.)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
This whole thing is very unclear. If the problem is that the supports were just sitting on soil and have sunk in, then I don't see why any new joists are needed. Just placing concrete slabs for support on the ground is not the correct solution, nor will it pass code. But then maybe the rest of the deck won't either.
The correct starting point here is to pour concrete footers that extend below the frost line that the supports will rest on. Then you will have something that will last. What else is wrong with the deck or what else is needed to correctly support it can't be determined from the rest of the description.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.