Viewing 21 posts - 1 through 21 (of 21 total)
  • Piling costs for house extension?
  • Bimbler
    Free Member

    We’re trying to build an extension on the back of our 30’s semi-d, owing to it’s position on a hill and the proximity to a freshwater drain piling looks like the only/best option for foundations anybody know the rough cost per metre for augered piles? Cheers

    footflaps
    Full Member

    A friend had 3 or 4 and it cost £5k inc all the concrete lintels on top etc.

    Bimbler
    Free Member

    Thanks footflaps, any idea of the depth of the piles your friend had?

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    jam-bo
    Full Member

    not sure on costs yet but have a look at grundomat piling. considerably less machinery required if you are on an awkward site with difficult access.

    nickjb
    Free Member

    Does it matter how much per metre? Surely you won’t know how many metres you need until they start digging. That’s always the big unknown with footings

    Rubber_Buccaneer
    Full Member

    I think nine piles to approx nine metres cost us somewhere between £7-9K, can’t remember the detail now as it was about a year ago. I’d get quotes for the piles and ground beam together. This was a relatively easy site.

    wrightyson
    Free Member

    Used grundomats for driven piles a long time ago, driven welded sleeves then subsequently filled with concrete and bar to create your “mat”. Also believe we did some with what i think was called a bunny rig which is tracked and can be driven through a doorway to augered piles. What is the slope like by the way? Don’t see why this would dictate piles over trench. Have you got an engineer on board?

    Rubber_Buccaneer
    Full Member

    Does it matter how much per metre? Surely you won’t know how many metres you need until they start digging.

    Before deciding on piling and getting quotes we had a couple of core samples taken so we had a rough idea what was down there and how deep.

    Scienceofficer
    Free Member

    If you look at the BGS onshore geoindex, they have some layers showing publicly available borehole records. Chances are there will be something reasonably near your house to give you an idea of what you might need to do.

    Bimbler
    Free Member

    Thanks all. Just got a basic quote back, in less than a day, and it doesn’t seem unreasonable. Thought that costs may put the kibosh on the whole thing.

    Budgeted for 8m piles based on the fact that, as mentioned, we are on a hill but on “made-up” ground, how long does ground remain “made up”, my house has been there nearly 80 years, I think it’s either clay or chalk underneath that. Also the freshwater drain is about 5m deep from the level where the extension is to be built.

    one_happy_hippy
    Free Member

    Have you had a Ground Investigation Commissioned? If not commission a ground investigation. Many local authorities now wont give you planning without a GI for foundation design and contamination analysis for human heath.

    For the cost of £1500 or so its worth it for the long term not falling downness of the extension.

    The number of extensions we see that have incorrect foundation design / no foundation design that are subsequently falling down / have to have remedial works is staggering. The funniest are where the Building control turn up when its 90% built and ask to see the GI report and then subsequently order GI work that ends up involving demolition of the extension to re-found it.

    RE: Made Ground – if its ‘Made ground’ and not an engineered fill than it’ll always be made ground.

    munrobiker
    Free Member

    http://mapapps2.bgs.ac.uk/geoindex/home.html

    Here’s the geoindex Scienceofficer was referring to.

    Made Ground is Made Ground, pretty much regardless of age. A ground investigation would give you the definite answers you need – it’ll tell you how deep the Made Ground is, what the strength of the geology below it is and the piling contractor is likely to need this information, and some chemical testing (the made ground can contain sulphates which are aggressive to concrete piles). It will cost around £2,000 but could save you the cost of several metres of pile, and in the long run mean you have the right foundations and the thing won’t fall over. Do you know what foundations your house uses? It’s relatively simple to figure it out if you don’t mind doing some labouring.

    If you want some back of a napkin advice about the geology beneath your house then my email is in my profile (I’m a geotechnical engineer)- while the Herts Geol Soc thing is useful for a general overview geology changes surprisingly quickly.

    Bimbler
    Free Member

    Phew. Who do I approach about a Ground Investigation?

    Yes I saw this, Geoindex thingy unsure what layer to use, returning white chalk on 1:625000, can’t find anything more than that, although when I dig about 30cm into the ground of the lowest terrace in my garden it’s clay?

    Scienceofficer
    Free Member

    Use the borehole layer. You might want to look at superdicial geology as well as the solid you’ve already found.

    A foot into the ground tells you nothing. As Munro biker says, made ground is made ground. It’s a generic term for ground that is literally made of the detritus of previous land use or unspecified tipping of whatever is around, and usually compacted/consolidated by the tipper traffic or a dozer if you’re lucky.

    As such it has no specification and variable qualities such as resistance to slip, over-pressure, subsidence, free drainage and the like. It’s basically an unknown, which is why a ground investigation is usual.

    Rubber_Buccaneer
    Full Member

    For us (new build not extension) it went

    1. Have geological survey (or whatever it was called) completed
    2. Decide piling was the only viable option
    3. Have piling design drawn up (sizes, reinforcement, etc) to suit the house
    4. Get agreement from building control
    5. Sort out party wall agreements (the further down you go the further away this applies)
    6. Choose piling company and make sure you keep the piling log if required by building control or for LABC warranty etc.

    al2000
    Full Member

    We had a similar situation, 30’s semi, extension on hill, proximity to storm drain (3m deep).

    We were advised by a structural engineer to go with piling and commissioned foundation designs accordingly – Severn Trent said no, they are very wary when it comes to unconventional foundations.

    After working with building control, a different engineer, and our builder we specced deep trench foundations which were acceptable to Severn Trent, and much cheaper than the piles. Still bloody expensive, mind.

    steve_b77
    Free Member

    Roger Bullivant are an all in one solution, GI, Pile design etc.

    I’m pretty certain Terrawise do domestics too.

    There are numerous companies out there.

    The BGS will give information on the general area and in addition to the original plans for the house you may find an architect / designer / engineer willing to sign off on this information alone; however if as you say the property is in fact built on made / non-consolidated / engineered ground a full GI survey will be required, at the very least there will be a mac-probe test and quite possibly window sampled coupled with SPT to ascertain the exact make-up of what your house is actually built on.

    one_happy_hippy
    Free Member

    I’m in the GI industry – depending on where you are in the country I can either help or point you in the correct direction.

    ChrisE
    Free Member

    For something like that, driven steel tube would normally be cheap. Augered piles (CFA) are a bit overkill.

    Make sure they include a warranty.

    I do about £300k a year of piling but all big stuff

    C

    Bimbler
    Free Member

    Just thought I’d update this thread, had the piles “done” to structural engineers design in late November, 9 piles (managed to lose 1 due to a design change) to a total of 87 linear metres. Deepest pile was 15m! No we’re not building a car park. Came to about £6.5K.

    The ground was a smorgasbord of clay, chalk and sand.

    A further cost was the ground beam, the pilers, who I think didn’t really want the job quoted something like £10k. Managed to do it ourselves for £7k-£8k.

    tom200
    Full Member

    Good to see someone in hi-vis 😀

    Who did the GI in the end?

Viewing 21 posts - 1 through 21 (of 21 total)

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