Rough cost of these extension plans? (London)

itravelforchurros

Hi all - we're considering doing the following extension of our 3 bed semi in zone 4 London. Any ideas on rough costs in today's climate? We'd be looking at a mid-level spec.

• Convert attached side garage to liveable space (18 sqm) and include a 6 sqm bathroom
• Build on top of side garage (18 sqm) to create a bedroom and a bathroom
• Extend out to the rear on the ground floor by 21 sqm on full width and then further 15 sqm on original house
• Build on top of rear extension to create a 9 sqm bedroom 
• Knock out two chimney breasts (on party wall)
• Move a boiler downstairs
• Knock through two 3m walls to create open plan, will likely need support beams + brand new kitchen

Any ideas appreciated.

Doozergirl

I appreciate that you're new and can't post links or pictures, but the list isn't a lot to go on! 

How much do you want/need it to cost? 

Can you post a broken link to a previous rightmove advert, perhaps?   Someone here will fix it.  

itravelforchurros

I want it to cost as little as possible ideally. I don't have a link but it's a typical 3 bed semi with side garage. I.e. 2 decent sized bedrooms and a box, bathroom upstairs, downstairs kitchen, dining and living. 

I thought the sqm would be a decent amount to go on but maybe not!

Doozergirl

63 square metres, in several extensions plus a garage conversion and we don't know if the garage is capable of holding an extra storey  - easily £150k before you even start bashing the existing inside around and buying kitchens and bathrooms.  So throw another £50k at that.  

itravelforchurros

Doozergirl said:

63 square metres, in several extensions plus a garage conversion and we don't know if the garage is capable of holding an extra storey  - easily £150k before you even start bashing the existing inside around and buying kitchens and bathrooms.  So throw another £50k at that.  

Wow! Thank you. I feared it would be around the £200k mark. In a realistic case scenario do you think it would be done (with a project manager friend managing the different trades individually) for:

• £2k per sqm for the building work so £126k (63 sqm x £2k)
• £1k per sqm for the garage conversion so £18k (18 sqm x £1k)
• £10k for two bathrooms 
• £10k for the kitchen
• £3k for the two chimney breasts and moving the boiler 
• £5k for rewiring
• £4k to remove the two load-bearing walls + install support
• £20k for internal decor (underfloor heating on 36 sqm, carpeting to cover 45 sqm, some fixtures)

Grand total of: £196k

Doozergirl

It looks light, to be honest.  £2,000 a metre is not very much, particularly when that 63 square metres is split up into different extensions - the smaller they are, the more expensive they are.  I would have budgeted £2,500 before the massive price hikes in both materials and labour, and not in London.  

£10k is not a mid range kitchen in a large house, it is bottom end.  Ditto bathrooms, bottom end.   

Moving a boiler can easily cost £3k in itself, more if the boiler doesn't meet regs and needs to be replaced.  

£5k bottom end wiring for a decent sized house.  Damage also occurs to the entire house.  

All of it light, let alone for London. 

itravelforchurros

Doozergirl said:

It looks light, to be honest.  £2,000 a metre is not very much, particularly when that 63 square metres is split up into different extensions - the smaller they are, the more expensive they are.  I would have budgeted £2,500 before the massive price hikes in both materials and labour, and not in London.  

£10k is not a mid range kitchen in a large house, it is bottom end.  Ditto bathrooms, bottom end.   

Moving a boiler can easily cost £3k in itself, more if the boiler doesn't meet regs and needs to be replaced.  

£5k bottom end wiring for a decent sized house.  Damage also occurs to the entire house.  

All of it light, let alone for London. 

Well that's scared me right off! May have to re-think this house purchase   

I guess I could also prioritise certain works but would hate to rip up the house later on when we're settled in. 

Doozergirl

Oops.  Sorry 😬

weeg

You need to allow for fees too - planning and building control, architects and engineers. I'd guess they'd eat up the better part of £10k?

ObserverOfLife

A friend of mine is having a big extension in the suburb of London and the going rate is £2.5k per square metre so you should budget for that. I would add on 10% of total budget for contingency. Material costs are also rising so may end up being more expensive at the later stage. 

FaceHead

As a general rule, don't think that having something built is going to be less expensive than buying it. If your budget won't stretch to buying this sort of home in the developed state, it won't stretch to buying a wreck and developing it. 

The benefit of a project is getting exactly what you want, and getting to live in something when it's newly done up - unless you're a property developer doing it on a shoestring, it's unlikely to come out less expensive than just buying the house you want. 

(Side note, could the garage be converted, and then built on top of? It seems unlikely the foundations were designed for a first floor, so it may need demolishing and re-building, at much more than 1k/msq)