Piled Foundations

[stender]

I have a conservatory of the type where you have about 2ft of brick work then conservatory. I'm considering changing that into an extension i.e. continue brickwork up and put a roof on with 2 or 3 velux windows and keep the existing french doors.
Question is.... The foundations were piled due to clay soil which has resulted in nearby non piled structures pulling away from houses. eg porches and conservatories.
How Can I tell if the foundations are ok to support a one story or 2 storey extension?

 

[freddiemercurystwin]

Call up Building Control and speak to the inspector who deals with your area, with any luck he'll be a good'un and will ask you to dig a trial hole or two so that he can pop out to have a look at your foundations. If he's happy with what he sees he'll say so if not he'll tell you why not and what he'd expect. Being the inspector dealing with your area he'll be familiar with the local ground conditions.

Just read that you'll be keeping the french doors so strictly speaking you won't need to get Building Regs approval though its till needs to comply with any relevant regs. If you're going to all that work though why not get it approved and give yourself the option to do away with the french doors.

 

[^woody^]

Call up Building Control and speak to the inspector who deals with your area, with any luck he'll be a good'un and will ask you to dig a trial hole or two so that he can pop out to have a look at your foundations. If he's happy with what he sees he'll say so if not he'll tell you why not and what he'd expect. Being the inspector dealing with your area he'll be familiar with the local ground conditions.

A trial hole, for piles?

I doubt any BCO is qualified to assess piled foundations via a trial hole, or would even entertain it.

And what about the pile caps and beams? I'm sure any BCO would want more than a cursory glance to prove aadequacy

 

[freddiemercurystwin]

Ahh I read his thread that people in the area had done piles and he had strips. My bad!

 

[stender]

Theres no way to see the piles. There were 4-6 put down and then 1-2m foundations concreted on them if I remember right. This is why I am asking the question about hhow you could assess? I'm hoping the company that did the conservatory have records and can provide plans but I dont want to use them for the work.

Re french doors I want to keep them they are only 2-4 yrs old and are fine

Would anyone be able to give a rough idea of how much it might cost?
about 15ft square to basically brick up and sloping roof with 2 or 3 velux in roof.

 

[Static]

You would need records of the piling depths, size and layout as well as soil investigation information. I would be surprised if the conservatory people put in piles and ground beams suitable for a 2 storey extension.
Chances are you would need to underpin with new mini piles.

 

[GuyK]

Hi Stender,

I am in exactly the same predicament that you were in. I want to replace my Conservatory with a single storey extension with flat roof and lantern. My foundation is mini piles with a stainless steel beam apparently, any advice from your past experience would be most welcome.

Thanks Guy.

 

[jeds]

Hi Stender,

I am in exactly the same predicament that you were in. I want to replace my Conservatory with a single storey extension with flat roof and lantern. My foundation is mini piles with a stainless steel beam apparently, any advice from your past experience would be most welcome.

Thanks Guy.

You'll be lucky if Stender is still watching this thread.

My own extension was piled. 5 piles were driven at 115kN and all refused between 8m and 8.5m, which gives you about 45kN/m. That was done with a small hand held mini-rig, which is about as small as it gets. A track rig would drive to much greater pressures. The load per metre of an average extension is between 15kN and 20kN/m, so the capacity of the piles is more than double the requirement.

Of course, you don't know exactly what your pile capacity is and there is no way of knowing without the original piling specification. But I'd be very surprised if it wasn't well inside of what you need for your proposed conversion.

 

[GuyK]

Thanks Jeds, I appreciate the info this helps me a lot.

Guy