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Depth of foundation wall

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swazimatt

Civil/Environmental
Aug 19, 2009
286
I recently had an argument with the architect for a single storey house. The contractor had levelled the site and was roughly 250mm below the original ground level.
The contractor had then excavated his trenches for strip footings (700mm x 230mm with 220mm concrete filled concrete blocks as foundation wall). The trench was only deep enough for the concrete footing and possibly 2 courses of blocks (220mm high each block) before he reached the finished floor level of the ground floor slab.

I was satisfied with the excavation as he was through the topsoil and into good hard gravel layer below.
The architect threw his toys out the cot (as no doubt they are all taught to do at university!) and said that the building code requires four courses of blockwork below the ground floor slab.

The building code in swaziland is left over from colonial days and i only know one old engineer who has ever seen it.

My question is why would the code mention that?

The only reason i can think of is for projects that do not require an engineer (single storey houses in swaziland do not) by specifying 4 courses plus foundation you are looking at between 0.75 and 1m below original ground level, and that should get you through the bad stuff in most situations. So if you are in good material and your footing will not protrude above ground or into your floor slab you should not be controlled by depth.
 
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I don't know if there is any required frost depth in Swaziland, but it is 18" here, and that necessitates a minimum of two courses of fully grouted block.

The footings, strip or spread, are usually required to be buried a minimum of 7" into the soil to inhibit walking of the foundation duiring a seismic event.

Otherwise, you got me on the four courses. Unkless the frost depth is deeper, which I highly doubt, maybe he has had too many four course meals?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
 
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