Tommy C

I may be building a block wall in a basement which has a slab floor. Here's a dumb question....is the frost line altered on a basement floor? In other words, for the footing of this new block wall, would I need to go 36" below the slab floor for the footing? Or is a little 6" deep footing OK, since this is a basement that is already 5 feet below the grade?

MALCO.New.York

The purpose of the the wall would dictate the need or not for a footing.

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Tommy C

There is a framed 2x4 wall there now (rotting). Beyond the wall is a crawlspace. So the homeowner wants me to build a more permanent block wall there.

concretemasonry

The frost depth is referenced from the distance below the EXTERIOR soil level. A basement(even unheated) is not subject to the same conditions as an exterior wall.

For a non-bearing wall in a basement, I would suggest 6" block and definitely not 8". - Lightweight would be better. An 8" wall is expensive and too heavy, especially inside and existing basement.

If you have faith in the condition of the slab it is possible to eliminate a footing. Drill a few holes and probe with a bent coat hanger to see how thick the slab is and if there is anything below it.

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Dick

Engineer, designer and consultant recently active domestically and internationally on construction and design in about 35 countries.

Tommy C

Dick, that's what I thought. I would just feel weird laying block on a slab.

I have not driven out there to see the slab yet...so I am unsure of the condition exactly. The homeowner says there are a few hairline cracks. House is 40 years old.

Assuming the slab is 4", would it be wise to proceed laying a non-load-bearing block wall on this slab?

neolitic

I wouldn't want to assume the responsibility.
What if it doesn't hold up?
Load bearing or not, there's always going
to be some idiot come along later and
assume that it is, after you assumed that
the slab would be okay, and then....
I would push for an 8" deep footing for
everyone's best interest.
2¢

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MALCO.New.York

Build the wall on the slab.....Non-Load Bearing............NO PROBLEM!!!!!

Other posters.....Stop with the confusing BS. Dividing wall....Simple install.

__________________
Something to One may be Nothing to another!

Ultimate Wisdom---------
http://www.youtube.com/watch?v=_k1Ug...ture=rec-HM-r2

neolitic

On an already cracked slab where
"best practice" was install an untreated
frame wall for a crawl space.
Yep I trust that whole set up.

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concretemasonry

neolitic -

The poster reported a few hairline cracks, which should not be a problem. He will be looking to to determine the actual conditions and was alerted as to what to look for.

If the slab is sound and not undermined after probing, it should be fine for the conditions supplied.

Certainly is it far better that what a wood butcher would put up. If the slab is not sound, the scope of the job changes and a footing will have to be installed after cutting out the concrete. The owner has to put up with the mess and inconvenience.

__________________
Dick

Engineer, designer and consultant recently active domestically and internationally on construction and design in about 35 countries.

Tommy C

Once I scope this out in person I'll have a better idea of how to tackle...I'm thinking this will be a good job for the winter since it's indoors.