PWA and the 6m / 45 degree rule

kingandy2nd

kingandy2nd

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Hi Folks,

Making slow progress with my detached garage build, but I've got to the point of getting quotes for groundworks.

I live on former sand dunes, so a special foundation was always going to be needed - raft or piles.

My initial thoughts had been a raft foundation, as I am a touch over 3m away from the neighbours so I thought piling might be a bit close. On speaking to the groundworks specialist (that also did my extension), he's said that often a raft is not suitable if the ground is not stable and that the labour and materials involved often mean it's more expensive than piling.

He's pushing to do piling on the job. I asked him about needing a PWA because of being less than 6m away from the neighbours (and obviously digging down quite far for piles) and he said a PWA isn't needed for piles.

All the houses around here are built on piles, so I guess we wouldn't be piling down further than the neighbours - not that we could tell how deep their piles are.

So my questions are:
- Is the feedback regarding rafts a fair assessment, or am i getting pushed towards his preferred way of working?
- Should I be concerned about the PWA if I go down the piles route?

Thanks
Andy
 
Best you consult a PW surveyor as I think the piles do form the foundations and therefore will come under the act


We had to do this for our extension / piling
 
The key word is excavation, and piles are not excavation.

Despite the Internet having lots of sites saying that piled foundations invoke the Act, those sites do not clarify why, and I've never found any precedent to confirm that piled foundations are excavation.

Rafts may not always be suitable for shifting sand.

You should really involve an engineer to report on the ground and suitable foundations. There will be costs in that, and costs in potentially choosing one or another foundation type, that may or may not avoid the PWA. You may need to work out some scenarios and risks/costs.

If you are minded to pile, then if these go in quickly, the Act can't be applied retrospectively.
 
^woody^ said:
The key word is excavation, and piles are not excavation.

Despite the Internet having lots of sites saying that piled foundations invoke the Act, those sites do not clarify why, and I've never found any precedent to confirm that piled foundations are excavation.

Rafts may not always be suitable for shifting sand.

You should really involve an engineer to report on the ground and suitable foundations. There will be costs in that, and costs in potentially choosing one or another foundation type, that may or may not avoid the PWA. You may need to work out some scenarios and risks/costs.

If you are minded to pile, then if these go in quickly, the Act can't be applied retrospectively.
Click to expand...
Thanks Woody. I noticed the same when I read the details of the act, there was a focus on the excavation so I think it would be a technical point to consider whether piling was excavation or not.

The only diagrams I can find regarding the PWA and piles are those where the new building is piled and the adjacent property has a traditional (shallow) foundation. This isn't the case here, so the odds that my piles go significantly further down compared to next door in order to invoke the 45 degree rule is questionable.

The quote for the piling (9 piles to 4m) is £7.5k plus vat. My extension went down 8-12m in places, so at £35m a metre for the extra depth it's probably going to be about £11-12k all in. I do take your comment on board about the engineering report, but pretty much everything around here is piled, so can see that I'd pay for a report (which I guess won't be cheap) and then end up with piles being recommended anyway.

Good point about the act being retrospective...don't want to be naughty, but equally it's questionable at to whether the PWA applies, so might be a situation to seek forgiveness (of the neighbour) rather than permission as this build isn't coming in cheap as it is.
 
TBH, piles are not going to affect anyone's foundations at 1m or 6m. So even the spirit of the Act - excavation and foundation slip, wont be relevant.

The only potential thing I can think of that may be classed as excavation would be skimming the topsoil to allow for the ring beam and pile caps. But if that was done prior, say a bit of landscaping that is not part of the Act then that does away with that connection.

I think as long as you advise the neighbour that there will be a bit of noise, and maybe vibration depending on what system you chose, then that will give them chance to move the Willow plates and Ming vases.
 
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