Moving a support post

RaH · 03-07-2010, 07:14 AM

I'm in the process of moving a support post in my basement. The house is 2 story, truss roof and has an 8" steel beam in the basement. I'm moving the post approximately 16" from its current location. My question is how deep to make the footing. I'm looking to cut a 2' x 2' pad and go 24" deep with a tapered hole. I've read that 8 to 12" would be sufficient in a similar set up. This seems light to me?

Just Bill · 03-07-2010, 07:49 AM

There is no forst line under a basement slab, at least not in the lower 48. And in theory, you are already on undisturbed soil, so it does not need to be deep. Check local code for your requirements. I know 16" is not far to move a support, but are you sure that does not upset the balance of the support structure???

tpolk · 03-07-2010, 08:08 AM

adding 16" to a load span could make a diff. get it checked first

RaH · 03-07-2010, 08:23 AM

The steel beam has two posts supporting it. The basement area is small - 20' x 24', and there is another post holding the beam. The posts are set with equal spacing between the openings. I had an experienced builder look at it and because of the short distance being moved he thought this was not an issue. Having some difficulty with specifics in local codes in my area on this subject, which is why I'm factoring in some overkill in the footing depth. safe vs sorry. Thanks for the help.

Daniel Holzman · 03-07-2010, 08:31 AM

There is no specific rule that tells you how deep you need to be. Typically the footing is sized based on the specific type of soil, i.e. organic soil is junk, and cannot be used, hard pack glacial till might be rated up to 6000 psf. You need to read the code, and check with your local code enforcement official. I assume you are pulling a permit, as this is a permanent structural modification to the house. Some codes set minimum depth for footings, some set minimum sizes.

As to the required depth, you don't kinow for a fact that the soil is undisturbed, your house could be built on fill. Once you open up the slab and are able to look at the soil, an experienced, qualified person (typically an engineer) can determine what the allowable bearing capacity of the soil is. Based on the load you are going to pick up, the qualified individual can then determine how big a footing, and how deep, it needs to be.

walkman · 03-07-2010, 09:48 PM

2'x2'x12" is typical, but the hole should be square to the bottom, not tapered. Use rebar in the hole.

Bigger issue is widening the span. Inspector will probably want an engineering stamp if you're pulling a permit.