Rear Extension

[LBS85]

We’ve found a property were interested in buying and adding a double rear extension on the back, a 3m ‘simple’ permitted development job. In theory it’ll allow us to have a much bigger kitchen/diner, possibly a study or play room and upstairs a larger family bathroom with either 2 doubles or 1 master & en-suite.

Firstly, is the general rule of thumb still £1k-2k per square metre for the ground + 50% more for the upper still reliable? And are these figures for a plaster finish with electrics & plumbing or do they include decorating/bathroom/kitchen fitting? I’m going a bit boss-eyed with all the different types of estimate that google throws up & would really appreciate some clarity!

Secondly, regarding permitted development we know the 3m double storey shouldn’t be a problem, but if we wanted to add a conservatory or further single extension later would we need planning permission? If that’s the case I’m wondering if it might be worth just doing it all at once under full planning.

We’re in Kent & it’s a semi detached property. Yet to measure up properly but as a guess: 3x5-6m out from the rear on both floors...maybe 2x3m as an additional single storey if we feel the need.

 

[^woody^]

Instruct a local surveyor to comment on the development potential and costs, don't base spending thousands on a random internet forum and Google.

 

[LBS85]

I’m trying to gauge some rough guidance before I bother spending potentially wasted money on a surveyor!

 

[Notch7]

Building works prices are quite high in the South East.

Also there is likely to be a big variation from Tunbridge Wells / Sevenoaks area to the East Kent regions like Sittingbourne.

My guess is that you should be thinking more than £50k less than £100k

 

[^woody^]

Lol. Not "waste" money on a surveyor, but waste money and time on all the other costs.

There you go then, the internet has spoken and it's a £50k margin of blind guesswork. Time to put the deposit down for several hundred thousand pounds on the house of your dreams.

 

[LBS85]

There’s no need to be so nasty, do you not have anything better to do with your time other than troll forums giving critical responses to people who are just trying to have a general discussion?

 

[Leofric]

is the general rule of thumb still £1k-2k per square metre

Would you be prepared to accept an estimate that could vary between £1k-2k per square metre anyway , quite a variation
Wouldn't the agent/surveyor selling the property have an idea of the building costs in your area

 

[LBS85]

Building costs very much depend on what you’re having done (a 20sqm ground floor extension cost will be quite different to a 20sqm double floor)...and estate agents are no more builders than I am.

And you’re correct, it is quite a variation, for the reason above not to mention area of the country among many other variables.
If the general rule of thumb IS still 1-2k per square metre, we will consider having work done to the extent of our budget & time frame, allowing for 2.5k per square metre + contingency. Which at present, it does.
If it’s gone up a bit it may mean we need to rethink the work we’d like to do, or consider saving for longer.

 

[JP_]

I think if you have that much to play with you'll be OK. My 53ish square metre single storey extension was 63k, so about £1200 per square metre. That got me plastered, electrics, plumbing, a gas pipe for cooker, rendered externally. I decorated myself. In Chelmsford. Also had 2 chimneys removed in other part of the house. I think I got a good deal overall though. 2 builders quoted £110k-£120k for the same work. Another said £40k but I didn't trust him to stick to that so sent him packing.

 

[LBS85]

That does sound like good value Jonbey, was that recently?

If we can we’ll go for just a 5x3 on the two floors, so a much lower footprint which I imagine will push the £/m2 up slightly. We have some handy friends to fit kitchen & bathrooms so that’ll be a few cases of beer and dinner on us

If we can’t do a straight forward double storey we’ll try for a wrap around - 27m2 on the ground (12 ish of which would be a garage) and as much as we’re allowed upstairs. Probably 15-22m2. We know a wraparound is likely to come in more expensive on the whole so will try to avoid it if we can.

 

[^woody^]

There’s no need to be so nasty, do you not have anything better to do with your time other than troll forums giving critical responses to people who are just trying to have a general discussion?

Just because you dont like the answer does not mean its nasty. Don't be a snowflake.

What you dont seem to understand is that unless one of the posters here is in the same postcode area as the house you want to buy, and their house just happens to be almost identical, with identical access, drainage, ground, and construction, then you can't hope to get a realistic idea of costs or even potential to extend.

Someone has suggested a potential cost with a variance of +/- £50k and you like that and think it's valid, when infact it's actually nonsense to think that an extension estimate can be £50k out. And it's more nonsense that anyone would take that and make an offer on a house with an intention to develop it, and then potentially find that they can't even build an extension or if they could it could be double the cost of the internet guess.

As for wasting money on a surveyor, then that's a very narrow view of what paying for a survey actually is for.

And this is the best advice you will get on here, but it's not my fault if you don't even realise it.

 

[Notch7]

Building costs very much depend on what you’re having done (a 20sqm ground floor extension cost will be quite different to a 20sqm double floor)...and estate agents are no more builders than I am.

And you’re correct, it is quite a variation, for the reason above not to mention area of the country among many other variables.
If the general rule of thumb IS still 1-2k per square metre, we will consider having work done to the extent of our budget & time frame, allowing for 2.5k per square metre + contingency. Which at present, it does.
If it’s gone up a bit it may mean we need to rethink the work we’d like to do, or consider saving for longer.

It sounds to me like you have a realistic budget.
I think it helps to get a builder to do the basic build with electrics, plumbing, plastering. Then get your own trades for flooring, decorating, bathrooms, kitchens.
These are things that can be separate and you can put some ballparks in for each item to get a feel for your overall budget.

I appreciate its a chicken and egg: you want to know a rough guide on cost first to see if its anywhere near your budget
Its seems like your project maybe say £50k - £60 for a plastered shell, then you would need to add on your other bits.

 

[LBS85]

Thanks Notch7. Yes chicken and egg is the perfect phrase really. If I am way off which the research I’ve done then we may not even decide to the property. However if I can get an idea of what is achievable in our budget we can make decisions around that. Thanks for the info

 

[Leofric]

Building costs very much depend on what you’re having done (a 20sqm ground floor extension cost will be quite different to a 20sqm double floor).

You don't say !

.and estate agents are no more builders than I am.

I know that ,I didn't suggest they were builders but some estate agents also have chartered surveyors in the firm.

And you’re correct, it is quite a variation, for the reason above not to mention area of the country among many other variables.

Don't take offence but are you asking the questions or providing the answers It isn't too clear