Rear extension quote

nicnic77 · 25 July 2019 at 2:40PM

A few months ago I was quoted by a builder for a 6m x 6m rear extension with GRP flat-roof. The quote was £53,650k + VAT. Bi-folds, roof lantern, new boiler, kitchen fit not included.

I've reduced the depth of the extension plans to 6m x 4.5m and asked for a re-quote. The price is now £48,500k +VAT (£5150+VAT less).

Does any of that sound right? I've read everywhere that the average cost of an extension should be £1500 - £2k per square meter.

At £1.5k per m2 that would mean:

6m x 6m = £54k
6m x 4.5m = £40.5k

The builder is saying that the costs are due to supporting a bay window above the new rear extension and installing a warm roof with GRP.

Thoughts please?

FreeBear · 25 July 2019 at 3:15PM

Labour will be the single largest component of the quote, so a reduction in the amount of materials isn't going to have a huge impact. You have a saving on 3m of brickwork and 9m² of roof & floor (down from 36m² to 27m²).

For a saving of £5K, you'd be better off going for the full 6m extension. Or put another way, you'd get a third more floor space for just 10% more money.

bengalknights · 25 July 2019 at 3:20PM

As above its costing you less per sqm to have the larger extension.

However do get 3 quotes to ensure it competitive.

nicnic77 · 25 July 2019 at 11:34PM

6m is no longer an option. I put 4.5m through planning in the end.

So does £48,500 plus VAT seem reasonable for 27m2? Crudely that works out at £1800 per m2.

When the figure of £1500-£2000 per m2 are banded about, is that usually always plus VAT? Also is that for the basic brickwork and roof - no bi-folds or roof lanterns etc?

Doozergirl · 26 July 2019 at 12:09AM

There isn't a rule.

There are so many different ways of building. Even if you built within the same specification, it will cost differently per square metre because each individual square metre of that building involves a different level of work.

A 10X10 metre building will cost less than a 5X20 metre building built with the same products, despite them being the same square meterage - the rectangle requires 25% more labour and materials in foundations, for a start.

You're bang in the middle of the rough estimates you're comparing it to, and your builder has clearly shown variables, which to me indicates a maturity in estimation.

There is no science, only art, when it comes to pricing.

phill99 · 28 July 2019 at 12:39PM

You must get out of the habit of simply comparing square metreage. It is very naïve of people to do so. You are not understanding the intricacies of pricing. A 6x 4m roof will cost the same in labour as a 6 x 6m roof. And the cost differential in materials is marginal. As Freebear above suggests, labour is the biggest cost and there will be very little reduction In labour to build the smaller extension.

Londoner_1 · 29 July 2019 at 12:48PM

nicnic77 wrote: »

6m is no longer an option. I put 4.5m through planning in the end.

So does £48,500 plus VAT seem reasonable for 27m2? Crudely that works out at £1800 per m2.

When the figure of £1500-£2000 per m2 are banded about, is that usually always plus VAT? Also is that for the basic brickwork and roof - no bi-folds or roof lanterns etc?

I'm also looking to build an extension 4.5m x 5.8m, pw side is complete as sharing with neighbour but im getting quotes of £30k, £36k £38k and £45k ex vat based in East London. The 30k is very tempting and includes extras but i think its too low. Block construction with felt warm roof, 2 quotes have gpr covering.

Doozergirl · 29 July 2019 at 4:24PM

Don't have a felt roof. Times have moved on.

And £30k really is silly, especially if it includes extras. It's been calculated crudely by a builder that still hasn't worked out what we've been trying to explain.

Doozergirl · 2 January 2020 at 9:23PM

I don't understand.

How did you save money?

flea72 · 3 January 2020 at 12:50AM

Doozergirl wrote: »

I don't understand.

How did you save money?

By getting a lifetime supply of spam for free

malky39 · 25 February 2020 at 9:44PM

7m x 3.5m extension, tiled pitched roof

Electrics standard 4 double sockets, 1 ceiling pendant, 1 extractor vent and 1 smoke alarm

Plumbing Utility Room, hot and cold water supply, sink waste pipe, first fix only

Joinery Standard skirtings and facings to extension, New pocket door to existing

bathroom, 3 velux windows as per drawing.

Plaster All walls and ceilings in extension plaster finished

£37500 Quotes varied from this to £47000

Rear extension quote

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