Reducing foundation costs

[bsr]

I was discussing our extension plans with my brother who's a civil engineer (not structural). We'll need piles and beam & block flooring due to clay soil, trees within 2m of foundation and FFL between 600mm and 1200mm above ground level.

I was explaining that I understand the ground beam is a lot of the cost. He suggested it would be much cheaper to extend the piles above ground up to say 450mm below FFL, then to span the piles with steels and build directly off them. He thought steel would be much cheaper than the cost of the ground beam and have ample strength.

Would this work and is it ever done? I haven't got an SE yet as we are at planning stage. I would need 16.4m of either beam or steel. A set of four 203x102x23 UB with a 275x10 welded plate would be about £1.5k or 250x250x10 SHS would be about £2.5k. Obviously I don't know what beam would be needed for a 3m span but either of those is a lot cheaper than a ground beam. The extension would be single-storey, conventional construction with gable pitched roof.

I guess you would still need the outer skin to go below ground level for comestic reasons so what would you do there? Clad with cement boards and slips? Any sort of brickwork would presumably need a foundation so then you're back to step 1. You would also need to restrain the steels somehow e.g. shot nailing or bolting into the piles.

 

[^woody^]

How are you going to stop the beams rusting?

 

[Deleted member 281264]

I was discussing our extension plans with my brother who's a civil engineer (not structural). We'll need piles and beam & block flooring due to clay soil, trees within 2m of foundation and FFL between 600mm and 1200mm above ground level.

I was explaining that I understand the ground beam is a lot of the cost. He suggested it would be much cheaper to extend the piles above ground up to say 450mm below FFL, then to span the piles with steels and build directly off them. He thought steel would be much cheaper than the cost of the ground beam and have ample strength.

Would this work and is it ever done? I haven't got an SE yet as we are at planning stage. I would need 16.4m of either beam or steel. A set of four 203x102x23 UB with a 275x10 welded plate would be about £1.5k or 250x250x10 SHS would be about £2.5k. Obviously I don't know what beam would be needed for a 3m span but either of those is a lot cheaper than a ground beam. The extension would be single-storey, conventional construction with gable pitched roof.

I guess you would still need the outer skin to go below ground level for comestic reasons so what would you do there? Clad with cement boards and slips? Any sort of brickwork would presumably need a foundation so then you're back to step 1. You would also need to restrain the steels somehow e.g. shot nailing or bolting into the piles.

I'm in the same position as you at the moment, it's difficult trying to decide whats best. Had a quote for piles at around 6k but they don't do ring beams, not sure how much that is going to cost seperately. any ideas? 8x4m area

also have you considered removing the trees?

 

[Nakajo]

You mean like this? https://bit.ly/39Nlmey

 

[Markbon]

Has anybody else told you piles is the best way? I was in that position once with trees 3m away and clay soil but when I got Building control out he just made me go down 1.8m 0n on side and 1.5 on the other 2 walls. Saved a lot of money.

 

[Deleted member 281264]

Has anybody else told you piles is the best way? I was in that position once with trees 3m away and clay soil but when I got Building control out he just made me go down 1.8m 0n on side and 1.5 on the other 2 walls. Saved a lot of money.

Common theme here engineers insisting on piles. But what happens if you don't listen to the engineer and then problems occur, does that mean they are absolved of any liability?

 

[freddiemercurystwin]

Encasing the beams is not hard but perhaps not cost effective given you're on a cost saving excercise.

 

[^woody^]

Common theme here engineers insisting on piles. But what happens if you don't listen to the engineer and then problems occur, does that mean they are absolved of any liability?

Of course, the person you listen to is responsible.

 

[Deleted member 281264]

Of course, the person you listen to is responsible.

Interesting, so can BCO's/council hold the same type of liability as a structural engineer? I was not aware of that and assumed it was better to listen to the SE.

 

[^woody^]

Interesting, so can BCO's/council hold the same type of liability as a structural engineer? I was not aware of that and assumed it was better to listen to the SE.

No, the council hold no liability for what they approve, advise or fail to notice

 

[Nakajo]

Well, same with AIs; just take a look at those T's & C's

 

[Notch7]

How are you going to stop the beams rusting?

Case them in concrete with 50mm min cover

 

[Notch7]

A set of four 203x102x23 UB with a 275x10 welded plate would be about £1.5k or 250x250x10 SHS would be about £2.5k. Obviously I don't know what beam would be needed for a 3m span but either of those is a lot cheaper than a ground beam

I'm not sure about that.

I did a 6m x 6m orangery for a client (who conveniently "forgot" to mention the big patio where it was going used to be a huge pond)

From memory the SEs charged a few hundred quid for a rebar schedule, the reinforcing bar cost about £1500 and then it was the cost of the builders to tie it all together and cast the concrete....which is probably no more work than the steel beam option....which will need encasing anyway.

From memory the 8 driven piles cost about £6k


Have you considered a raft?

 

[^woody^]

Case them in concrete with 50mm min cover

I'm not sure 50mm is enough, but even so, by the time our thrifty friend has paid for shuttering and concrete (and ancillary costs) he'll be cursing his bro and his big ideas in a very uncivil way.

 

[^woody^]

Well, same with AIs; just take a look at those T's & C's

AI's are engaged under contract and so have all the liabilities and responsibilities that come with it including negligence.

Bare in mind that just because someone tries to impose their T&C's, it does not mean that they can or that the T&C's are actually valid and enforceable.