Pile Foundations and different options

[OurBuild2023]

We have had plans drawn steels calculations done and permission granted with stipulations on foundations because we live net to a canal. Our original costing for foundations alone was £9K this has now spiraled to £50k plus ( more if they have to dig deeper than quoted). Does anyone have any experience with a similar situation? would be interested to hear. TIA.

Why did it go up so much? Though 9k sounds ridiculously cheap. How many piles?

Can it not be built on a reinforced raft foundation?

Was it originally designed on piked foundations? Or rafts/strips?
Was the original design based on a ground investigation? Has one subsequently found unforeseen adverse ground conditions? Assuming it's a CRT/EA owned/managed/maintained canal, did the design include permissions and licences from CRT/EA?
The cost of construction materials has skyrocketed on the last year or 2. Deii is ending on the type of pike, it could be that they are not made in the UK, so obvs transport costs will have massively increased too.
Do you need sheet piles to cut off seepage from the canal as well as foundation piles for your property.?

C4tastrophe That was for normal foundations before we realised were informed we require pile foundations.
Diyextension This is out of our remit, i guess i haven't put enough information in my original post. Will add at the end here.
IbizaToTheNorfolkBroads We were advised of this option by our Architect & structural engineer this is our 1st project of this type. We are next to the canal on a hill with lots of trees around us. I'm trying to find out if there could be different options as we havent got a clue. It would be great to have some information to go back to the Architect & Structural engineer with so we don't look as clueless as we actually are 🙄

Is this stipulated by Building Control? You could phone the officer back and clarify. It might be a standard comment for properties near water and they just want confirmation the soil conditions have been checked. Piles are usually needed in soft ground or where there is a settlement risk. I know someone who had a house built right next to the Thames on steel screw piles but that was in the flood plain.

Is it s new property or extension by the way?

NotMeNoNo The original house is 100 years old with a existing extension possibly 40 years old.

This is what they said.

3. Prior to the commencement of development, details of the proposed risk assessments and methodology for the excavations as well as details of the type of foundations to be undertaken shall be submitted to and agreed in writing by the Local Planning Authority and thereafter implemented in accordance with the agreed details. Reason To comply with Policy SP.31 of the Wyre Forest District Local Plan and Paragraph 174 the National Planning Policy Framework as Excavation and the construction of foundations have the potential to adversely impact on the integrity of the waterway infrastructure.

Structural engineer here. Depending on the soil type, you may need piled foundations if you're in a close proximity of trees. If you're in clay and within trees influence zone, the foundations may as well need to be in excess of 2m+ deep and piles may prove to be more economic. It all depends on tree type and soil type. Check nhbc building near trees (google it). If you're in London, you're 90% in clay.
Also, if you're near a canal, the water table may be quite high and shallow foundations may need pumping out water, which again would increase the price.
Quite surprised it went up so much though. Although given current economics and jumping prices, it may as well be the case.

Sorry OP but I think you were terribly naive to assume you'd only need standard foundations when you say the property is on a hill, close to trees and adjacent to a canal....did you not seek any advice before putting in your application??

You say you are near a hill. Is the canal built on an embankment. The soil conditions beside a canal could well be extremely poor depending on whether the canal is cut out of the ground or built above it. You definitely definitely need a very experienced structural engineer and you absolutely need to draw their attention to the possible issues re the canal.

I am currently building next to the Thames and we were very close to needing to pile. Instead, we have dug 2m foundations and even with the cost of the digging, muck away and extra concrete, it is still much, much cheaper than piling. I hope you find a solution.

Stickytoff canal would have been cut out, we have already employed and paid the structural engineer to be advised of this at the very last hurdle. We are not builders just wanted to extend our home without any previous experience or knowledge 🙄

cowsaysmoo thanks for your reply, I shall show my husband all of these reply's tomorrow.

menareallthesame this is what I'm trying to find out, if/ is there is another way!? It's just so frustrating when you do everything by the book and pay for all the survey's you need and then get this thrown in at the end. Ignorance is obviously not bliss 🙄

It will depend how close to the canal you will be going, how much load, and the relative levels, as well as the stability of the existing cut/bank. Suggest get your engineer to explain ideally with a diagram, why the piles are needed. Since it's your money that's a reasonable thing to ask.

NotMeNoNo Thanks for that 😊

We had the same with our extension, it was only 3.6 x 7.2 m, we are on a hill and on made up ground so we’re told we would have to pile. We did only pay about £10000 though but this was just over a year ago for 7 piles. There are obviously many variations as to what may be needed in your case, I think ours was quite straight forward and not near water.

I should add the 10000 was for the piling only, not the rest of the foundations and floor.

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