minimum depth of footing .

22 Sep 2009
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United Kingdom
We currently have a conservatory that we would like converting into a single story extension.
I have dug down and discovered the footings are deep of concrete with the dampcourse about 3 brick courses above this height.

Am I right in thinking that we will have to have new footings dug ?

If so to what depth?
I live in south northants if this helps with depth of footing required.

many thanks in advance.
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It all comes down to your local building control department. Give them a ring and tell them what you are looking to do. They will probably be able to pop out and take a look and let you know if you will be able to reuse or have to redig. Also means you don't end up paying lots for buildings notice to then decide its going to cost too much due to the foundations not being up to scratch

I have just done exactly the same proceedure and got the good news they were good enough for my single story extension.
Soil types and foundation depths are peculiar to each individual area and there is no set precedent. A default depth setting of 1m is recognized as the accepted norm.

Here in Staffs we have a sub-soil variation of pure clay through to sandy soil with ducker stones. The sandy-ducker stone variety being the best type upon which to build. Clay sub-soil is nowt but trouble.

If the soil type is good at say 600mm and unlikely to change whether you are at 800mm or 1200mm then bc will accept shallower than the standard 1m depth.

However, if there are signs that the soil is non-virgin, made up ground or that there are deep drain pipes close to the dig, then b.c. will insist the foundations are dug deeper.

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