Extension too small, builder says "tough!"

[tumdedum]

Can anyone help or suggest what I can do next?
I've just had an extension built on my house. I selected a builder based on recommendations and provided him with accurate plans from a (very expensive) architect. The builder has now built a single storey extension that is considerably shorter than what the plans indicate.
I didn't realise the extension was too short until the kitchen planner came out to measure up. I put faith in the builder that he would be able to take the plans and translate them into an accurate building. Let's be clear here, this isn't some fly by night one-man-band builder, but a proper and (previously) respected local building firm.
I'm obviously really angry about this and don't think I should pay the full amount. The walls are up and plastered, the roof is on, they can't feasibly knock it down and start again.
But how do I work out how much is a fair amount to knock off the bill? If I just took the value of the bricks that weren't used, that doesn't take into account the knock-on effects such as the kitchen units I was planning to put in there can no longer do so, my washing machine won't fit in anymore, the pitch of the roof looks silly, etc.
And where do I stand legally in terms of not paying any amount that is fairly decided? It's getting nasty now with the builder who is refusing to complete the job (2nd fix electrics, carpentry and plumbing) until he receives payment for the milestone that the building came under. I've had 1st fix done, but I'm going to struggle finding an electrician who is going to be happy to take someone's half job and finish it?

There are several other problems with the work that has been done so far. This project was estimated to take 4 months - but I've been without a home for 10 months so far. It's a nightmare. I'm losing sleep over it. I feel close to a nervous breakdown.
Does anyone know who I can turn to for honest advice?

How much smaller is it?

I think you need legal advice. Are people going to want to buy a house with an awkwardly sized extension?

@wowfudge:
The part of the extension that is too small is a long thin utility room.
It's 6" thinner than it should be - which doesn't sound much, but it equates to being 10% smaller than the plans indicated. (and now nothing fits)

@Tollygunge:
Do you think any local legal firm would know how to deal with this sort of situation or should I search for something in particular.

I wonder if I need to see some sort of surveyor to go over all the problems with the build and quantify them in some way?

To confirm, six inches short? that being 10% than the plans indicated so the plans suggested 60 inches (five foot) and you have 4.5 feet width?

He hasnt followed your plans and you haven't got what you ordered. I wouldn't be paying him at all unless he puts it right.
You wouldn't pay for a rolls Royce and walk away with a mini would you?
What's the point of an extension if you now can't fit your things into it? It's his mistake not yours don't give him a fkin penny if it's not right.
Seek legal advice asap.

6" so 15cm?

I can't help sorry but there might be other sites where you could ask. You poor thing though.
Try searching for Building not built to spec or something. MN has something similar.
Did you have a written contract?

Are you measuring internally or externally?

The architect provided internal and external measurements. Both of which are incorrect. It's 15cm too thin. I know that doesn't sound a lot written here.
But it's a pantry and a utility room.
So the internal measurements for the pantry should have been 1555 x 1000
It's actually 1400 x 1000
The utility room should have been 1555 x 4335 It's actually 1400 x 4335

What was your contract with the builder and what does that state about tolerances and measurements?

If it is 10% too small pay 90% of the bill! If he thinks 10% doesn't matter he can accept 10% less!

Actually your figures just seen show its only one length that is 10% out. Work out what the square metrage should have been v whst it is now (by multiplying length x width). Add 2 rooms together. Then work out the percentage difference. It won't be 10% but less as only one length was incorrect.

Just did calculations - still 10%

I'm surprised builders are still trying that fraud.

Years ago it is said that the builders for an estate of houses pocketed a lot of profit by charging for the full size and building smaller. They saved on bricks, concrete, groundwork, labour... everything.

It's not a mistake. They actually have to deliberately order undersized excavations dug, and smaller roof timbers from the suppliers, recalculating from the plans. It's a fraud.

You need to go back through all of the documents / drawings to see where the error has occurred. Is it an outside wall? If so, is the difference on the architects drawings 300cm (the width of an outside wall?). Did the council approve the drawings as drawn (I have seen planning permissions say that an extension has to be set back one brick's width from the front of the house)? Or is it simply that the builder made a mistake? What have they said?

I'd lawyer up I'm afraid. How stressful and how dare they think they can get away with it.

Before forking out on the legal advice I would try to google if there is any allowance in law for variance between plans and actual build.

I have no experience of building industry etc but in my line of work I deal with suppliers who deliver products and there is always +/- allowance for variance to spec.

You absolutely can ask them to knock it down and make it right. I'd also ask for any costs caused by the delay to be swallowed by the builders.

You need an experienced buildings surveyor. They can advise you on what constitutes normal tolerances on size (which TBH it does not sound as if this is). Probably worth them inspecting the quality of the work to date too. He should be able to advise you how hard it would be to make the necessary changes and how much it would cost.

Also, do you have a written contract? Does it say that the builder has to build according to the architect's plans? Does it specify a completion date? You may well have a legal claim against the builder.

Get some legal advice - you may well have free legal advice as part of your home insurance.