Piling or Standard Foundations

muskoka

Architect says needs pile 17'...(due to various trees) structural engineer says piling not required, subject to trial hole Builder I'm 'likely' using says no difference in piling with ring beam to digging foundations - bearing in mind very narrow access lane to house & removed dirt can only be transported by transit tipper. Absolutely no chance of getting even a mini skip down the lane Struggle to get a car down there

Is just a standard 25 metre ground floor extension.

I've desperately tried to get hold of an independant piler this evening, but can't find any local

If anyone can throw any light on price difference (how long is a piece of string, I know) I'd gladly appreciate it

Thanks:)

ab7167

Have you had any kind of ground investigation done? Foundations need heave protection when in proximity to trees if there is clay in the soil. Interested to know how the architect has determined the length of the piles....

muskoka

Architect has now asked for trial hole to be dug, then to notify authority to inspect same, and local authority to advise if piling required which is fine BUT I'm thinking if costs are very similar to pile as against to dig standard foundations....then piling could be the way to go due to extremely difficult access for removal of dirt (from digging standard foundations)

No idea how architect has come up with 17' piles There are various trees within 20/30' of property though, including Cherry, Llelandi and also a huge tree (dont know what it is, but something like an oak tree- probably protected)

If for example piling is much more expensive, then standard foundations will have to be dealt with

GuidoT

Everything else being equal a structural engineer will know more about the type of foundations than an architect. Therefore providing the structural engineer knows what he is doing then you should go with him. But all of this is irrelevant until you dig a trial pit as the structural engineer may conclude piles are required.

Piles are generally more expensive than a strip foundation, I can say no more than that without knowing the depths quantity etc.

ab7167

If there is very difficult access for soil removal, you may have difficulties getting a piling rig on site. There are smaller rigs available, but I don't know exactly how small they go. You can get them inside building though, for remedial works to existing structures, so I'm guessing they come small enough to fit through a door? A piling contractor would be able to offer better advice on this.

In terms of soil removal, even if you pile you will have to dig trenches for the ground beams. This is likely to be around the same width as standard footings, but probably shallower. There will then be reinforcement to fix in these trenches. Standard footings will be deeper, to compensate for the trees, but no reinforcement. I am assuming you are installing a suspended floor?

Tucker

I priced up both as I had do a trial hole as all the houses on my street were put on raft foundations.

Basically, piling worked out about 3 times the cost of standard strip foundations.

The piling company I got quotes from did not include digging out. They just came in calculated it, piled, did the steelwork and poured the concrete.

The best quote I got for that was £2200+ vat for 15 sq metres.

There's more digging out for standard foundations, but the cost was way less, so I was very happy to not need the piling.

CashisKing

I would get a quote from a piling company then you have a firm idea rather than speculating.

Look up the Zurich tables/NHBC tables (PM if you cant find them) for Height distance for the trees to see your likely required depth for trench fill and work out a price for the different types of clay (high/med/low shrinkability).

Soil testing can end up costing lots of money if you get the companies on site with their rigs etc.

If you decided you wanted to trench fill you could dig a hole to the depth you think the foundations will be and take a 1kg sample and send it for testing.
E.g CMT testing is about £50+VAT then you will know what the soil is like.

tommytadge

Get a trial pit done and let the structural engineer inspect and determine the way forward. Architects know next to diddly squat about foundations and structural loading.

stef73

When we had our extenstion built it was the planning dept that told us we had to have a piled foundation . We had to have a core sample taken to determine the depth . We are a mid terraced house with the only rear access through 2 gates (not double width) Both firms core sample firm and piling firm had rigs capable of fitting through gates. If memory serves its was £120 for core sample .

ormus

ive seen those mini rigs where access to almost anywhere is possible. they drive mini piles into the ground, no or little excavation required.
no idea on prices though.

there was a DIY SOS type prog on telly recently, where the rigs were shown in use.

muskoka

Thank you one & all. I really appreciate your input Having today spoken to Building Control, architect & structural engineer, subject to a trial hole- it seems that piling won't be required.

Goodness knows what removal of dirt for foundations are going to cost though. Absolutely no chance of a skip lorry getting anywhere near the house (transit tipper only way I can think of, but gonna increase the cost doubtless). Oh well