Hi! I have post-and pier foundations under my old 2-story wood farmhouse in Northern California (it never freezes). They were amateurishly renewed 20 years ago using standard building-supply piers, and have sunk as much as 7 inches in some places. The soil is flat clayey bottom land. I want to replace many piers (the decision versus perimeter foundation is already made). I’ve done all kinds of building work including concrete, but never this particular job. The area is a crawl space about 2 feet high.
Can anyone please give me advice about what type of jacks to use? What is the best method of inserting a new post — should it and the post bracket be installed into the fresh concrete, or the post forced in after the concrete has set (I mean while the beam is temporarily supported with jacks and shoring)?
I intend to make forms and pour concrete for piers of about 2 feet square, or is that larger than necessary? How sharply angled should the sides of such a pier be?
I will very much appreciate any help and comments. Thank you!
Replies
The first thing I would do is to speak with an engineer and have him calculate the bearing capacity of the soil and give you a rough sketch of the pier. I would then pour the pier according to his specs and after it sets up to 75% strength (about three weeks) I would jack up the floor, insert the new post and fasten it per engineers specs.
Hope this helps, good luck
Have you looked into getting a permit for this? Here in LA, they'd probably require you to put in continuous footings or grade beams if you have a lot of piers gone wobbly.
Two ft. square might be too small. Only a soils engineer who knows your area can say for sure. But if your piers are on 4 ft. centers, as is typical, that's half way to a grade beam already. Get it designed right, or you risk putting all your effort into yet another not quite good enough foundation.
When I did mine, I used one 20 ton Norco bottle jack from Otto Service Co., a 12 ft. piece of w8x15 steel, and loads of cribbing and shims. But I didn't have a big area to lift, or anywhere near as far to lift it. You might want to go with more and bigger steel to let you do more per setup.
Or, maybe even get a house mover to put the whole house where it belongs so you can do it all in one shot. Of course you'd be paying for their steel and cribbing for the duration. (OTOH, I still have that w8x15 in the garage from four years ago....)
-- J.S.
Thanks to Saw Horse Const. and John Sprung for your helpful answers. They are appreciated!