Extension cost (London) is this reasonable?

[ThisOneNoThatOne]

I'm just looking for some advice on the cost of a house extension. I know it'll be hard for people to answer this without seeing the plans, but I'm close to signing a contract with a building firm and I'm getting cold feet about the cost- it just seems so expensive!

We have a 1930s semi, and we're planning a double side extension, and at the back a part single and part double extension (extending by 3m at the back and 2m at the side). We're also remodelling inside and having 3 bathrooms & underfloor heating on the ground floor.

I've had 3 quotations- (£150, £180 & £210k) although with the cheaper quote it was quite basic so I think there will be lots of extras. I'm thinking of going with the £180k quotation and with extras such as flooring, kitchen I'm hoping to go no further than £215k.

Is this reasonable? I'm wondering if ive picked the wrong builders to get quotes from and have chosen expensive ones?! The builder I like is holding a slot in Feb for us but needs us to give him an answer asap.

Thank you!

My OH is a main contractor (although premium finish - mainly does west London) and he said what you've been quoted is cheap. He said if you get anyone else further down on price, they won't be making any profit at all and will just need to make the money back by leaving bits out on the quote and then adding back in as extras. Also if the quotes are too cheap, it's because they're using cheap subbies who end up being unreliable as if they get offered another job offering more money they'll leave yours and it'll be delayed. Good luck with your project but go with the contractor who is most trustworthy and who you get along with-not the cheapest! It's the biggest investment you'll probably ever make, don't scrimp. Pay a fair price and you'll get happy reliable quick contractors.

Thank you geeup that seems very wise advice!

May be true for some contractors but we have an architect supervising the work, and the way the contract is done, he can't charge extra if he finds problems and if any work is not to standard the architect will ask him to resolve it. He's already asked him to change the damp proof course so the water drains to outside if it gets between the layers but no extra charges. I wouldn't feel confident to question complex parts of the wall construction, but the architect can talk on the builder's level.
I think the important thing is to get a trustworthy contractor with a good contract, and then don't add extras unless you put it in writing.

Sounds about right to me. Decent building work is expensive.

If you know people who a builder has worked for and have seen how they do the work/what the finish and aftercare is like then personally I would go with that one.