Fair cost of Piling

[DarrenSL]

We are having a single storey extension built but on day one of the job it has been discovered that we need to have the ground piled. Now the piling contractor has quoted £2800 from 11m of piling which I felt wasn't too far off the mark. My building contractor however has added £2400 onto their quote for the dig & slab (was £3700 now £6100 excluding piling but incl survey fee of £700. Or to put it another way, now £9000 for 11m foundations and 5x4m slab).

I was expecting the original dig & slab price to come down as for £2800 I expect the piling contractor will be doing the dig and beam. Can anyone help me as I know nothing about piling and what is required? Is it fair to add cost if foundations and beam are already in place?

Many thanks.

 

[Static]

Chances are the piling contractor will only put the piles in, then your groundworks contractor will need to dig ground beams, reinforce and pour concrete then do the slab (be it suspended or otherwise). Adding the reinforcing element will increase the cost as speciallist fixers may be required..
Get more quotes..

Was the original house piled?

 

[DarrenSL]

Thanks for replying Static.

Yes the original house was piled. I was told before the job that the extension may need piling and it would cost roughly £2k. My structural engineer also said it would be about £2k. Now that contracts are signed and work has started it's significantly higher!

 

[^woody^]

Remember that the builders previously quoted costs for the [traditional] foundations and floor slab need to be deducted first, and then he adds the new price for the altered work.

So its not just a case of the builder adding additional costs

 

[DarrenSL]

Yes thanks Woody. It looks like they have forgotten to take off the cost of the original work. I contacted a piling company and they have given me a rough price of £2,600 including ring beam and BC calcs.

Is there anything unique about the floor slab when the foundations are piled. I wouldn't have thought so given that the slab isn't load bearing? So all I expect the builder now has to do is lay slab as originally planned and build straight from the concrete ring. Not sure why that would cost £5,400 + £700 utility survey.

 

[^woody^]

Really, this should be designed by an engineer - who will determine if the floor slab should be independent or not depending on the ground conditions.

 

[jeds]

All the piled jobs I've ever done had a suspended floor. Do you need a reinforced slab though. Would a beam and block floor not suffice?

 

[noseall]

Would any structural internal walls make a difference to the extra (piling) cost increases, if so are there any?

 

[DarrenSL]

Thanks again for you replys.

No, there are no internal walls so the only increase I could envisage is that they are doing something different to the 4x5m slab. There is steel going into the slab but I thought that would be the case on the original slab.

I suppose the question really is would having piling also add c.£2.5k on to the cost of the slab originally quoted at £1.2k? We have not had any calculations or engineer advice at this stage.

Not sure about the suspended floor Jeds. I am just following the architects plans and don't know the relative advantages/disadvantages of each.

I will get some more quotes. I avoided this previously as I am contractually bound with this company to do the work. I'm not sure what the penalty will be if I drop out now and get someone else to do the job. So far all that has been done is a toilet delivered to site and a test hole dug.

 

[^woody^]

You need to check your contract to see if it is still binding

The work content has changed, and it has significantly changed in terms of the foundations.

So it may be that the original contract is no longer valid, unless there are provisions for such a large change in the scope of the work

Even so, the contractor is obligated to give a new quote for the extra work - which is in itself potentially a new contract, and the quote must be fair and not hold you to ransom due to any other contractual arrangements - ie you can't be forced to accept a high quote just because you are tied in with the contractor for the rest of the work.

And you are not obligated to accept this quote and could get another contractor in for the foundation and floor slab work

 

[DarrenSL]

Thanks Woody, that's a relief!