Piling for extensions

maurice28

We're currently having an extension built, to add an extra room to the back of the house. While digging down to the required depth on the plans, before laying the foundations, the builders are yet to hit solid ground, the soil seems a little clay like. The building inspector is due to come out on Friday to see what they think and if piling is required so we'll know then but wondered if anyone had experience of piling.

The builders can see for example that the existing house has no piling under the foundations and would assume the soil is similar under the house itself. Does anyone have any experience of the need for piling for extensions when the main, existing building doesn't have it? I spoke to the council briefly before the work commenced and they didn't have a record of any other extensions in the area needing piling, but who knows!

We'll see what the building inspector says when they come, but I wondered if anyone had any relevant experiences?

stuart45

How deep have they gone? Do you know if your subsoil is shrinkable clay?

maurice28

stuart45 said:

How deep have they gone? Do you know if your subsoil is shrinkable clay?

I believe they've gone a metre deep so far. I'm not sure on the shrinkable clay question I'm afraid, just that clay does make up some of the soil (sorry, this is beyond my comfort zone of knowledge!)

Section62

maurice28 said:

Does anyone have any experience of the need for piling for extensions when the main, existing building doesn't have it? I spoke to the council briefly before the work commenced and they didn't have a record of any other extensions in the area needing piling, but who knows!

We'll see what the building inspector says when they come, but I wondered if anyone had any relevant experiences?

Building regs will require the extension to have adequate foundations - if that can only be achieved through piling then that's what you have to do.  The foundations of the existing house/building are more or less irrelevant (although the new work mustn't weaken the existing).

There can be reasons why piling is required when previous work was done without - for example the site of the extension could have been an old pond (filled in) with softer ground than the original, or organic material at a greater depth than the surrounding natural ground.  And sometimes ground conditions can vary quite significantly in the space of a few feet (in plan as well as depth).

maurice28

Section62 said:

maurice28 said:

Does anyone have any experience of the need for piling for extensions when the main, existing building doesn't have it? I spoke to the council briefly before the work commenced and they didn't have a record of any other extensions in the area needing piling, but who knows!

We'll see what the building inspector says when they come, but I wondered if anyone had any relevant experiences?

Building regs will require the extension to have adequate foundations - if that can only be achieved through piling then that's what you have to do.  The foundations of the existing house/building are more or less irrelevant (although the new work mustn't weaken the existing).

There can be reasons why piling is required when previous work was done without - for example the site of the extension could have been an old pond (filled in) with softer ground than the original, or organic material at a greater depth than the surrounding natural ground.  And sometimes ground conditions can vary quite significantly in the space of a few feet (in plan as well as depth).

Got it, thank you, that makes sense. I guess we'll see when the building inspector comes, thanks for the thoughts!

stuart45

One.of the.methods for testing is to drive a piece of 2x2 into the ground and see how easily it goes in. If it gets firm after a foot or so you might just need to go down a bit deeper. 
The square peg test was often used by BCO's.

Slinky

Good luck, our builders went down 9 feet which was as far as the digger would reach and still didn't find solid ground. We'd uncovered the site of a filled in well, as well as the old soakaway. We ended up with a reinforced concrete beam spanning the well.

maurice28

Slinky said:

Good luck, our builders went down 9 feet which was as far as the digger would reach and still didn't find solid ground. We'd uncovered the site of a filled in well, as well as the old soakaway. We ended up with a reinforced concrete beam spanning the well.

Ah nightmare, how much extra did that end up costing? 

EssexExile

I assume your builders are used to building in your area so know what to expect when digging for foundations. Wherever I've lived it's not normal to expect to reach something solid, just go down a metre, sometimes a bit more but not much.

Slinky

maurice28 said:

Slinky said:

Good luck, our builders went down 9 feet which was as far as the digger would reach and still didn't find solid ground. We'd uncovered the site of a filled in well, as well as the old soakaway. We ended up with a reinforced concrete beam spanning the well.

Ah nightmare, how much extra did that end up costing? 

£3300 with the new soakaway crates included. Not as much as I feared at one point. There was a huge amount of concrete made to fill the footings.

TELLIT01

EssexExile said:

. Wherever I've lived it's not normal to expect to reach something solid, just go down a metre, sometimes a bit more but not much.

I agree, firm ground but not bedrock.