Building/Extension help, could someone give me a rough estimate?

Wonderimg/hoping there are some experienced builders out there that could give me a rough guide cost for an extension, I realise it may not be easy without knowing exactly what’s involved but I’ll explain ….

So, I’m having some building work done, a single story extension on the side of the property (bungalow), it’s being done under permitted development and the building inspector says the work is good so no problems there. But, we are having a bit of trouble with the builder and rising costs, we think he may have underestimated the work, we just want to make sure that the final cost is not excessive and relates to the work done.

So, it’s a 3 x 12 metre extension, it’s on the side and to the rear so one wall is already existing but it extends 3m to the rear, 1m foundations, brick and block walls with insulation, concrete floor with insulation and screed finish, area divided into 2 rooms, flat roof going up into existing roof, 1 medium and 1 small window and outside door. That’s it, no plastering or electrics, just the builing work.

So can anyone give a rough cost? Maybe if your an experienced buider you’ll know by square meterage or something? We have been advised to get 3 quotes from other builders to get a figure but no one seems keen to do this.

Any help appreciated.

I’ve seen figures of £1000-£1200/sq m quoted before but suspect that includes more finishing work than you’re having done.

tbh, it’s going to be difficult to get other builders in to quote on a job that’s in progress I suspect.

Maybe sit down witht he builder and go through all of their expected costs and work estimates? It’s going to be about damage limitation at this stage. Get them to justify why it’s gone wrong thus far and why you shoudl trust any estimates they’ve made to complete the job.

You have got written quotes for the work that details what’s to be done etc? Go back to those with the builder too.

Have they started work yet?

doesn’t really answer your question but didn’t you agree cost and scope of work with builder at the start?

I had something vaguely similar built last year.

Same area, one room, pitched roof, screed floor, stud wall in-front of existing wall, all plastered. ~ £20K + windows (plus VAT).

Costs can vary depending on the details eg I had a very small extension to the kitchen, but it involved moving the main sewer, water main, gas main and boiler as all the services entered / exited through the wall I had removed. Cost £16k for 4 square meters of new floor space, but made a massive difference to usable space in the kitchen.

Something similar that came in at £28k complete, hope it helps as a guide

Janet & John’s Extension

Also

Single storey extension
Single storey extensions are simply an extension built onto a part of the house whereby one side (or more) of the extension adjoins the property and there is only the ground floor plus any basement built to it.

Main considerations here must be the size of the extension and its impact upon neighbours, how the roof will work with the existing building and specifically whether the same type of roof covering of the existing property can be used on the extension. Positions of flues, drains and excavations must all be considered.

In some instances planning permission will not be required for single storey extensions. Building control permission will almost certainly be required.

Typical costs can start at around £8-10,000*
(*Figures are rough estimates and may not be representative for the whole of the country).

Types of Extensions

Thanks everyone.

The builder has started, nearly finished, but everytime there’s been a problem, for eg. he had trouble cutting out some of the original concrete base where a prefab garage stood at the side, he’s moaned about the extra work, the extra time, the extra costs of getting equipment to cut it, and when the building inspector has said something needs to be like this and not what he thought, the same moaning again. We had a quote originally for something smaller which was good so thought we could go larger, he gave a rough estimate for extra costs of materials and work. Another problem is he was recommended by a neighbour, he’s their son, so we thought it would all be ok as we’ve known the neighbour for years and had no problems, so stupidly we trusted what he said.

Trying to nail him down to explain things has been difficult, he’s a very aggressive person and proven a real problem to deal with or talk to sensibly. I’m in the middle of writing to him to sort things out and getting some legal advice on where we can go and what to do now. He wants £30k, I’ve just measured it and it’s approx 10 x 35 feet, but that’s without plastering just bear block walls. He’s saying the extra costs are in meeting the building regs where he’s had to make a soak away, extra work for the air bricks, extra work and materials for the roof – all things I assumed he would have known about anyway before starting the job, we began to wonder if he knew what the building regs were? He keeps going on about the value it’s added to my property and we just say that’s got nothing to do with the cost of the work and it just ends up in an argument again.

But, it’s proving difficult to get other quotes, someone said that a local builder won’t want to go against another local builder. Speaking to someone else recently they said they’re having their kitchen extended by 3x3m and that’s costing £30k before they even have the kitchen put in. So it’s going to be difficult to know if this is fair or not?

I’d be looking to get a detailed breakdown of work done to date plus a list of what’s left to do with a quote to complete the work.

With no agreed budget for the new works and a change to the design after he quoted originally it’s going to be tricky though.

all things I assumed he would have known about anyway before starting the job,

Yep, he should have known all that to start and quoted against it. Sounds like he’s just not very good at quoting for stuff and/or doesn’t normally do complete projects on his own where he is responsible for everything.

I suspect he’s under costed it all and is out of pocket – which isn’t your fault.

What was your contract / agreement – build to plans?

He wants £30k

It all depends what he quoted to start with…

If his original estimate was 25k – then the extra may be OK, if there is extra work involved.

If his original quote was 15k – then he’s extracting the urine, and has underestimated to get the job.

footflaps and muffin-man, our thoughts exactly, we think he’s not quoted properly in the first place and is out of pocket so bumping up the price all the time, he’s suddenly adding on every little thing. He had plans which I drew up myself, I’m used to drawing up stuff on Autocad/2D Design myself, which showed the layout and elevations with dimensions but he claims never to have had them, so I’m trying to find out if the building inspector has ever discussed the plans with him.

His original quote was near to £15k and I budgeted £18-£20k expecting some increases, then it went up to £25k, then he said £30k to finish it, this led to a big argument outside the house, it was like an episode of Eastenders but after the watershed with lots of swearing and shouting (not by me by the way), I did record this and it’s quite shocking. Hense the reason for seeing a solicitor tomorrow with all the facts to see what we can do.

You have made it hard for yourself by not providing proper drawings and specification/schedule of works to quote on originally. You would normally expect the builders quote to reference these to make it very clear what he has quoted on. Did your drawings state that all works should comply with local authority regulations? You could get a surveyor to help you agree costs. It is very unlikely another builder will quote for you if they know the work has started.

Hi ajc, the builder knew I would be applying for a building notice and adhering to local building regulations, I even sent the details and drawings to the planning office to make sure it was all ok, we needed to have the building notice in place and first inspections arranged before he could start work. A surveyor, that could be helpful.

A surveyor may be money better spent than legal fees. If you and builder agree to a cost that an independent surveyor has reached it should be a fair outcome to both parties.

You have made it hard for yourself by not providing proper drawings and specification/schedule of works

plus 1

Personally, I would get him to stop work immediately, pay him for what he’s done based on the originally spec and quote and then find someone to finish it, having given them precise details and drawings.

Loads of Builders around, you just need to find one who talks your language.

lack of agreed scope is always a problem. Can be fixed though. If the design changed after you accepted his quote, and if you are not clear on amendments then a third party surveyor would be advisable before anymore work carries on. £30K tops is what I would consider if design has changed since he started though for a single storey. What roof is it?

Yep, I’d stop work. get a QS to cost up value of work completed so far and pay him off on that basis, if it goes to legal this should help cover you.

+1 Footflaps last comment. The bloke doesn’t know how to spec/quote and is making it up as he goes along. Get him to justify/itemise current and planned expenditure before letting him do anything else. Failing that, just get someone else in.

BTW, whereabout in the UK are you? Prices differ a lot in certain parts.

Ok, so maybe I didn’t spec what thickness of cellotex to use, or when to put it in, but he said this is what I’ll do, and this is when I’ll do it, and by this week we’ll be at this stage, I thought he would know these things and at no point did he say I can’t do this without this drawing or this spec or this schedule, yes in hindsight things could have been better, he has done a good job, been very bad with communication and letting us know how things are progressing, if he had said at the start it will cost this now we would have revised things to come within budget. I’m prepared to pay a fair price but I don’t think shouting, swearing, threatening to pull it down and agressive behaviour has endeared me to deal with him in a normal manner.

I think people are sympathising with the position you’re in now but also saying you could have helped avoid it and then offering a way to make progress.

The main thing, for me, would be for work to stop until you have all agreed a financial structure for the work to be done in and a clear list of what is left to be done.

wwaswas, that’s what I’m doing at the moment, work has stopped and I’ve informed him I’m sending some paperwork for him to respond to where I’m just outlining my concerns, what he intends to do to finish it, the final cost and terms for final payment, I’m getting a solicitor just to check the letter to make sure it’s ok and get some further advice, would just be good to know the work/cost is fair.

and….if you do discuss it further and he gets aggressive, walk away and say you are not prepared to discuss it unless he does so in a calm and professional manner.

sleepless, it’s a 3 layer mineral flat roof, supposed to be finishing it off with 2 layers of insulation with an air gap as per regs, but I’m wondering if he’s now going to say that’s extra

spacemonkey, I’m on the south coast, Brighton/Eastbourne way

I just got a quote for a 3x8m single storey extension which came in at around £26k. Not got any more quotes yet so not sure how that stacks up. It includes re-directing drainage, all plumbing and electrics to 1st fit, 4 velux windows in the roof, and 2 bi-folding doors. I’m having a small support in the middle of the opening as the steelwork for an entire unsupported opening was a bit high.

Mine doesn’t include any electrics or plumbing, 2 double glazed windows and a single door is included, he’s had to build a soak away for the roof guttering.

It’s a difficult one, I’m willing to negotiate final cost as sometimes I think it’s too much especially when I look at the link provided by Kona TC up there ^^ where it cost about £28k for a 8x30ft extension including new kithen, electric, plumbing, plastering, flooring, windows and doors, but that’s in a different area, and sometimes I think it’s resonable. Just wait to see how he reponds to my letter and then consider getting an independent specialist if not satisfactory.

Wobbiliscott – sounds similar to something I’m planning – where in the country are you to get that quote?

That is very 😯
For an un plastered un wired un plumbed space, and for that money I’d be expecting a proper sarna or similar roof, not pissing felt!
There’s not even a grands worth of concrete holding it all up!!!

Flat roofs are keeping us busy at the moment. have you had a down pour on it yet? you can do your own leak test, I am thinking of the prospect any snagging work really. Roof flashings/ details are also a bit troublesome. A QS is a good idea,a Surveyor could also QS for you and help with a snagging list, but without a scope to baseline from this could be a bit vague. at least the QS could price work to date though.

tor5, i’m near Derby. Its a local builder. Unfortunately he’s fully booked up to early next year so unless i’m going to wait (i.e. the wife) i’ll have to find someone else, but he was recommended to me. If you’re near me let me know and i’ll pass on his details.

wrightyson – it isn’t unplastered – it includes finishing the walls, fitting of flooring and two radiators i.e. leaving the space ready for furnishing and fittings – so not quite 1st fit – more like first-and-a-half fit.

Not yours wobblis, the op’s.

Wobbliscott – I’m in Surrey, so not much good I’m afraid – but thanks for the offer

Well, for anyone still interested, nothings’s been resolved yet, we’ve asked him for a breakdown of costs, receipts for materials and 3rd party work, receipts for money, list and costs to finish, proposed final cost and guarantees for all work, not sure he understands what we want, it was all listed out in a letter so not sure what we’ll get back from him. He came around and still insists on his cost, I’ve had others builders look and they say it should be finished to a ready to decorate finish for that price, not an empty shell, also spoke to a QS who seemed surprised it’s an empty shell based on the size and cost – he was asking if the electrics and plumbing had been done yet. Nightmare goes on …. 😐

Does sound like it’s going to drag on 🙁

The bloke is either incompetent or blatantly trying to rip you off.

spacemonkey, I think you’re right on both accounts, he even had the audacity to say it would cost more if he was doing it properly, ie receipts, and he would have to add 20% vat on top, it’s almost becoming a joke, especially when he said he had ‘a millionaire friend who would pay for a top solicitor’ 😀

Threaten him with a VAT man.

If he’s genuinely offering to do stuff ‘off the books’ and won’t issue invoices then they’ll be quite interested 🙂

spacemonkey, I think you’re right on both accounts,

Another problem is he was recommended by a neighbour, he’s their son,

IMO he sees you as easy bait for making a few grand quid as he’s had an easy introduction via his parents. Did you get any other quotes at the time? If not, and he knew this, he probably thought he could screw you for the extra.

wwaswas, that’s one thing we were thinking of doing anyway, even more so if we get no receipts and guarantees and I think Trading Standards will be interested to hear this too, they’ve already opened a case on the subject and the way he’s been dealing with us, there’s just no reasoning with the man, luckily I have conversations recorded including the threat to pull it down, him admitting he knew we had a budget but that doesn’t matter to him, and all the swearing and personal insults. It’s just crazy, he shouldn’t be allowed to trade, I can’t imagine he would treat other customers differently, he keeps going on about not ripping me off and he’s never had this sort of thing before! Really?? 😯