"mm" wrote in message
...
Same friend who is getting a new roof, I looked at her home.
She has a deck held up by 6x6 posts. There is a 10 or 12 foot span
that sags and needs another post in the middle.
I could use a 6"x6"x8', but I'm not sure how to keep it from going
further into the ground in a few years, or even tomorrow. I could pour
redi-crete around the base, but I don't see how that would do more
than slow its sinking. (I would use a jackpost to lift up the deck
to put the new post in.)
Or I could use a 6 to 8 foot jackpost, and build a 6x6 box around it.
Then if it sagged, say the post sank into the ground, someone could
just open up one side of the box and make the post longer. The box
would still be ok at its original length. Because of the grain and
warping, I don't think this box could look exactly like the other
posts.
Unneeded? details:
This time I'd actually do some work and she offered to pay me.
Her deck was repaired a few years ago, and the repaired part is the
part that is already sagging. This part is about 3 feet wide, 6 feet
off the ground, and 15 feet long, with 6x6's holding it up maybe every
5 or 6 feet except one part 10 or 12 feet long with no post.

You got some good advice on how to correctly anchor the base of the posts in
concrete.
Re jacking the sagged part, I just use a 20 dollar hydraulic bottle jack
from home depot to raise a really heavy elevated deck, by the main
crossbeam. Used a 4x8 x 4 ft long, laid on its side for a base, put the
bottle jack on it, then cut a 4x4 PT fir to about 6 feet long, and attached
4x4 sheet galv caps on each end, so wood would not split under
compression.. Cranked it up with ease.