Cost for an extension

[Trytosmilefor2025]

I am in the south east and have been looking at extending my kitchen for a while. The plan is just to add a standard 3 X 5 m extension at the back. Quotes are coming at between 40-50k. Most likely we won't get this money back any time soon, but it will make a massive difference to the way we use the house. I have also posted before about conservatories. That will be around 25k, but not open to the kitchen etc and given the price I think it might be best to pay a bit more for a proper extension....is this reasonable? Any thoughts?

Just for a bit more context: it's a 3 bed detached house that fulfills our needs really well (apart from the smallish kitchen/luck of dining space) and it's in a lovely/quiet residential area. Not keen on moving house given the hustle and costs involved....

That sounds reasonable to me. We've just paid 35k for a slightly smaller extension in the south west.

Thats a steal. We (London) wanted to add a 3x6m box extension on the back of the house and the build was coming in at 100k with the builders saying we need at least a 20% contingency. Thats without the flooring, kitchen, fixtures and fittings.

I did have quotes initially for 80k (clearly someone who wasn't motivated to do the job) so I am thinking that's fairly reasonable. Although we bought the house at the top of the market and we will unlikely make that money back...if we extend than really we need to stay put for the long run to make it worthwhile.

Have you had multiple quotes from builders with a good reputation?

I only ask as £40-50k seems VERY cheap. Off the chart cheap for the southeast.

If you go ahead, make sure that what’s included is fully documented as it’s not unknown for builders to quote cheap but then tell you later about loads of essentials that weren’t included.

I don’t think £80k is a price from someone not motivated to do the job - I think that’s probably closer to the usual going rate.

And yes to a PP, you need 10-20% for contingencies too.

We got multiple quotes for an 8x5m extension about two years ago (southwest). All ranged from £115 - £145k to first fix finish.

We’ve just done our kitchen, no extension but knocked a small utility wall down to make kitchen bigger and it has cost around £55k

I don't need a new kitchen, as reusuing the cabinets etc. The quotes I received are from 3 different builders and yes I have references and detailed quotes. It's just the shell that I need. But the comments above are getting me thinking....

I have done the same (knocking through to a dinning room), although a 3 years ago and it cost me 15k 🤔 but then again reused kitchen cabinets. I should add that the quotes received are from builders/firms that do not charge tax, I think with tax it will be more like 50-60k.

Gosh, that seems cheap. Also in the SE, extension of 2x7m 2 years ago was £65k (inc VAT) just for the shell. Total £90k once kitchen, flooring, extras and fees were added in.

Honestly OP, I'm not trying to piss on your parade, and maybe you have found builders that are just very competitive....

If they're not VAT-registered, how much actual experience do they have in building extensions? The VAT threshold is £90k, and that's turnover, not profit.

So either they don't do many extensions/big jobs or else they're doing things illegally which would cause me real concern for shortcuts in other areas like building regs, safety etc.

In your shoes, I would get a reputable VAT-registered building firm in to quote - and I'd show them the quote you've had and see what they say.

You have been ripped off!

Just was I was thinking! We did this a few years ago and it was 12k.

We’ve just had pretty much the same done in the last month. Original quote was £54k for kitchen extension - inc electrics, plumbing, steels, knocking down original exterior wall, creating a new bathroom, creating a new doorway, bifolds, and skylights.
it went over budget by about £10-12k in the end.

(all of this wasn’t including new kitchen, bathroom or flooring)

In hindsight, the company we chose to do the job wasn’t really experienced in proper extensions, with their strength being garden rooms and convsevatories, so my advice would be to go for proper building companies.

Ok, thank you all for your comments. Very helpful!

@Trytosmilefor2025 can I ask for recommendations? my quotes have come in a lot higher

I will look a bit more closely at the quotes and also at previous work. I do have a couple of quotes from a VAT registered building firms one at 78 the other at 67k. But to be honest at that price point (+any buffer). I simply won't be able to afford it. It will be too much of a financial stretch. Thank you all for sharing experiences!

I just had an estimate for a 3x6m single storey extension shell only plus velux and bifolds and it was £75k which was horrifying going to get a couple of others!

See the plan for mine is just to have a flat roof with sliding doors (as that's cheaper) and also refusing a window on the side....but still seems too cheap according to some so will investigate a bit more

I have pm'd you

thank you

This is very interesting. I'm looking for builders too in the SW. My neighbour just had a 4x7 m extension and it cost them £80k.

I'm hoping to knock down internal wall and replace conservatory with proper extension but have a budget of £40k. Hopefully it will be possible.

My understanding is that the costs will depend on the complexity of the project, e.g. the depth of the foundations, sewage on the way etc. And also, the type of roof/windows/doors etc. I just need the extra space

I’m in the SW. I’ve got a thread somewhere on here that follows our extension work from start to almost finished.

We went for a modular extension because it goes up faster, it’s a fixed cost, and it’s about a third cheaper. It looks and feels just like a regular extension and lasts just as well too. Unbelievably well-insulated - we don’t need heating in ours. We have our kitchen out there.

Cost came down from £143k to £96k.

If you’re on a budget, it’s worth looking into. We didn’t do it just for cost, but the cheaper price tag was a real plus.

@SpidersAreShitheads can you link to your thread please? I will be interested. I contacted Eurocell (one of the companies who do modular extensions) and the cost was around 60K in my case

can you tell me how your extension went in the end please