Basement

Rodney

Ok My customer has given me plans for a crawlspace foundation, His situation calls for a basement. All the loads should be in the same places for the supports as with a basement. I on the other hand am thinking that since the basement will have support walls all across the floors in the load areas, should I have to pour the footers in the load areas heavier as with a crawlspace or is the weight distributed evenly enough for the thickness of my poured floor. Sorry this may be a bit odd but this is my first basement.

mdshunk

Ummm.... aren't you gonna need an engineer's seal on these prints anyhow? I think the answer to the question is "yes", but if you need to get the prints stamped anyhow, the engineer's got a little work to do for you in this regard.

Rodney

no not in GA, Most residental is not required by an Engineer.

ConcreteGuy

Basic Engineering for Builders

When do you need an engineer? It's up to your local building department.

But a basement wall imposes no greater load beyond the original design of a crawl space. The only appreciable new load is from lateral pressure exerted by the earth fill against the wall.

You have a couple of options. You can pour a cantilevered footing with reinforcing dowels every 24", or, a conventional footing.

With the cantilevered footing you can backfill earth against the wall without a completed structure (framing). For 8' of earth fill, you would extend the footing about four feet beyond the outside face of your wall, on the side you intend to fill. With proper placement of reinforcing steel, this extended footing uses the weight of the earth fill placed on top of it to counteract (cantilever) against the lateral load on the wall.

The conventional footing would require you to erect the structure prior to backfilling the basement walls. The building structure serves as a diaphragm which supports the basement walls.

The most important thing is that you use re-bar out of the footing at a minimum spacing of 24" O.C.. And I would grout ALL of the CMU cells, not just those with reinforcing.

If you give me the height of earth fill, I can give you footing dimensions based on an engineer's charts (see the above link).

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A reasonable expectation becomes an assumption when it goes wrong.

Rodney

Its 7 foot.

ConcreteGuy

Your continuous masonry wall footing would need to be 3' wide by one foot thick with three #4's continuous. Dowel out #4's @ 24" OC for the vertical masonry, extending the dowels at least 24" above the footing. While constructing the masonry walls, lap the vertical reinforcing at 48 bar diameters, in this case a 2' lap. With your wall reinforcing spaced at 24", and minding the 2' lap for the vertical masonry lifts, grout ALL the cells using a Portland Cement and sand grout, paying special attention to the vertical masonry cells with reinforcing steel. The contractor should only wet the mixture as required to fill the cells and surround the reinforcing, without overwetting the mixture which increases shrinkage, decreases strength and decreases water intrusion.

It is also advisable to install a masonry bond beam near earth grade or slightly below the ground level framing.

This information is good only if you plan to construct the ground level framing prior to backfilling the basement walls. However, prior to such framing, you may place up to four feet of backfill without bracing the walls.

Price the installation of concrete foundation walls vs. masonry, while probably more expensive, it's a better product overall.

And pay great attention to the details regarding foundation drainage, waterproofing and final grading. All of your efforts will fail without it.

I am neither qualified to be an engineer, nor play one on TV, but keep in mind the importance of monitoring these activities. Further, make sure the earth will support the structure. If you are in a virgin earth cut, better, but just the same you need to probe the footing excavation. If you take a #4 re-bar (1/2" diameter rod) and can push it into the soil more than six inches, you might be a fat redneck...eh...heh heh, or you might have soil conditions unable to support a conventional structure using the above criteria.

I would wish you good luck, but only drunks and fools are thus served, lol!

*Sigh* I love earth and concrete.

__________________
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A reasonable expectation becomes an assumption when it goes wrong.