Guide to house extension costs

A question about : Guide to house extension costs

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I am in the process of planning a ground level extension to my house 3.5 metres x 4 metres apex roof. Is there a rule of thumbe for estimating building costs? For example Ј/square metre formula.

I just want to have an idea of roughly where the prospective builders should be giving their quotes.

Thanks

Tom

Best answers:

• Very roughly Ј1000/m2
• I think it would be worth you buying a copy of "The House Builders Bible" by Mark Brinkley https://www.amazon.co.uk/Housebuilder...309066-0616635
  This is a really helpful starting place for any building project or renovation, giving an indication of material and labour costs for most projects (or a guide where to find out current costs). Hope this helps.
• We had an extension built last year, slightly larger than yours is going to be, ours was 4m x 5m. It cost Ј11K all in.
  That was project managing ourselves, hubby done alot of labouring...i.e clearing site, digging footings and moving materials from front of house to the rear. Also he did the wiring and plumbing himself. The planning app and building regs cost Ј500 but vary depending on size of proposed extension. We also sourced ALL the materials ourselves as the builder wanted too much to supply and fit, so we supplied and he fit. Its worth getting a quote for both though.
  Definately worth having the tiled apex roof, the difference between this and a flat roof was only about Ј300 and it looks way better IMO.
  Last thing you MUST remember to do is to get a completion certificate from the building inspector. You will need this if you ever sell the property.
  Anything else you want to ask please feel free to do so, either on this thread or by PM.
• Have a nosey at this site too - it's not bad for getting an idea of costings and other things: https://www.house-extension.co.uk
• I live on Anglesey, which is hardly the most expensive place in Britain to live, but when I asked an architect for an estimate of how much the building costs would be to extend our bedroom out over an existing single-storey extension (basically sticking three walls on top of three existing ones and putting a roof on), he came up with Ј24,500+VAT, and the available space is only 4mx4m.
  This sum doesn't include fees for anything else (architect, planning etc.).
  From what I've been able to pick up of the Web, this is grossly overpriced, but should I bother getting a second opinion? I could only really even consider going ahead if the price was about half what the architect estimated.
  Regards
  Gareth
• Sorry - I didn't realise my post had been replied to - I'll look for an option that emails me in future when that happens.
  The current structure is fine to build on - in fact it's identical to one on the same side of the house on which we had built, with no problems, an extra bedroom 25 years ago, and is a simple 4mx4m square (or 3 sides of one).
  At that time, we had that work done - and a huge extension at the end of the building which exactly doubled the size of the house (which was already quite a big one) - all for Ј25K!
  Our recent experience only underlined the effects of house-building inflation over the years.
  Regards,
  Gareth
  Quote:
• I have started to obtain quotations for the proposed kitchen extension and shower room to our house. I have had detailed plans drawn up by an architect and I have written a detailed specification quoting the finish and services to be provided.
  It basically consists of gutting the existing kitchen (Approx 3 m x 5m) demolishing a conservatory (approx 3m x 2.5m) building a single storey pitched roof extension 3.5m x 4.2m (2.5 of the walls already exist), creating a toilet and wet room in half of the old existing kitchen (2.7m x 2 m). The build is to be completed as far as provision of all electrical, drainage and water services in a plastered shell with concrete floor all suitable for tiling or painting.
  I have put the plans and spec out to four companies whose work I have seen and know to be of a good standard.
  First quote is Ј35000.00
  This does not include the provision of any decorative finishes such as tiles or flooring or the supply or fitting of the kitchen or the supply or fitting of toilet and shower room hardware. Also the wet room waterproofing / creation is not included.
  This first quote is about Ј10K higher than I was expecting. Am I being over optimistic or is this builder trying it on? I am still waiting for the other three quotes to come in, but this first one is a bit of a shock.
• Where about in the country are you? Home counties / London prices are going to be a lot more than say, rural Lancashire.
  My initial reaction is that £35k is a bit OTT but getting it done for £25k is perhaps a bit optimistic. Rule of thumb extension cost is £15k. Also, what are the ground conditions like? Fylde coast is a lot more work than say Manchester (typically).
  Sorry just re-read it. It does sound high and even £25k might be OTT. Depends a lot on location.
• I suppose it depends on where you live as well.
  Personally I think Ј35000 for a 14.7m2 extension is steep.
  Our 2 storey extension is in the region of 30m2 and it costing us a few ЈЈЈЈ more than your quote and that includes VAT.
• Thanks Bob
  I am located in Derbyshire, midlands. Ground in mainly clay based and 2 and a half of the 4 walls that will form the new extension are already built.
  I don't won't to screw the builder down to the bare minimum, just a fair price for a fair job. I am still waiting on 3 more quotes so maybe they will be closer to my expectations.
  Thanks for your input anyway.
  Regards
  Tom
• I'm located in Derbyshire, our foundations had to be 2.2m deep do to the neighbours trees.
• The price that you have been quoted for your 30 m square two storey extension: To what extent will it be finished?
  For example does it include plastering, plumbing, electrical work, joinery etc?
  Thanks
  Tom
• Hi, i thought i would post in here as well as its the same topic.
  I am having quotes though at the moment for a small extension (about 12 ft by 8ft) and converting an existing coal shed into a shower room/wc.
  At the moment we have said that we are paying cash and the lowest price have been able to haggle to is Ј22500 + Vat so Ј26437. We have had a couple of quotes and both are around Ј25000. We are in Guildford Surrey.
  We are trying to get closer to Ј20000 but it seems this is near enough impossible. Does Ј25000 seem reasonable to anyone?
  Thanks
  Darren
• A friend of mine is having a toilet block / wash room built on the end of his business showroom. It measures 16' x 8' has a sloped tiled roof, built from block and rendered. Price for this with plaster finish, with all services electrical and water, excluding tiles and hardware is Ј12000.
  I am going to ask this same builder to quote for my kitchen extension mentioned earlier in this thread. I have not had my other three quotes back, but I am starting to get the impression that Ј35k is an inflated price.
• Just had another quotation for my 3m x 4m extension of which 2.5 of the walls already exist and the internal block wall to form the shower room. Ј50000. This is basically to provide the shell, so by the time I have added the fitting and kitchen units it will be well over Ј60000. This equates to about Ј5K per square metre!
  I am no builder, but something doesn't add up here. I have just seen a TV programme where a couple completely renovated a badly neglected cottage and added a two storey extension of greater area than mine, supposedly for Ј25K.
• Does anyone have an idea of a ball park figure for an attic conversion per m2? Will need beams moved as are W shaped at the moment.
  We wouldn't need a dormer though as there's plenty of headroom - velux windows would do.