Extension estimated costs

[chris101]

Currently in the process finding a builder to build a 11ft by 7ft rear extension and a side extension (8ft) both with pitched roofs and a sky light each.

The work involved 3 RSJ's, taking down 1 internal wall and 2 external walls, levelling flooring, replastering and finishing.

I knwo the above is very vague in detail but Roughly how much would it cost for the above or what would the range be?

Thanks

 

[joe-90]

£28,432 and 52p.

 

[^woody^]

Way out, Joe

 

[chris101]

We might be able to have the side extension joint to the neighbours wall (wall party agreement).
If we with this option, how much would it affect the costs of the extension work?

 

[joe-90]

Divide the full figure by ten then multiply by four.

 

[limerockconstruction]

£28,432 and 52p.

I'll do it for 28k for pound notes.

 

[indus]

What is the total m2 area of the proposed extension?

I know a lot of forum members find questions like yours a little annoying, and hence the replies

However there are some rough numbers you can use. In London if you give the work out in total to a decent main contractor builder then you'll be looking at about £1000/sqm2.

You might be able to knock a bit off if the job is simple with no complicating issues and no services involved (ie gas, soil etc)

I have an extension planned that is going to cost me more like £1350/m2 because of extra bathrooms being created, expensive brick/tiles being used to match existing etc.

So as a very rough benchmark (and I emphasise rough) you can use these figures to give you an idea.

There are of course lots of unknowns that could push your £1000/m2 upwards, but as you only wanted a rough estimate I hope that helps

 

[DeludedAussie]

What is the total m2 area of the proposed extension?

I know a lot of forum members find questions like yours a little annoying, and hence the replies

However there are some rough numbers you can use. In London if you give the work out in total to a decent main contractor builder then you'll be looking at about £1000/sqm2.

You might be able to knock a bit off if the job is simple with no complicating issues and no services involved (ie gas, soil etc)

I have an extension planned that is going to cost me more like £1350/m2 because of extra bathrooms being created, expensive brick/tiles being used to match existing etc.

So as a very rough benchmark (and I emphasise rough) you can use these figures to give you an idea.

There are of course lots of unknowns that could push your £1000/m2 upwards, but as you only wanted a rough estimate I hope that helps

But there must be economies of scale here - If I am doing a 10M wide by 4M deep extension (40M^2) then I would be quite shocked if they charged per metre because once you get a digger in there you can pretty much excavate the ground in a matter of days

 

[limerockconstruction]

Mate - surely you've got to read Indus post in a bit more detail. He said it was a rough idea - could go up and could go down depending on finish.

So although a digger could dig it all quickly thats great, but additional metres cost additional money - once you've dug out an extra metre of trench it needs filling with concrete, DPC blockwork, oversight slab and insulation & screed (or other finish). Then you have more block work, render, roof, plastering, skirting, painting etc.

I've just, this afternoon, signed a contract on a job which has come in at about £1,050 p/sqm - although there are variables - its a good benchmark. And weather you are shocked or not, when we are pricing jobs we need to have something to work on.....sq/metreage is an easy way for us to do it.

 

[indus]

You won't actually be charged by the metre as such but on average it costs about £1000/m2 for extensions. The builder has to price in stuff like electrics, heating, windows etc

Though people on here don't like to give 'estimates' over the internet because of all the unknowns I have found the £1000/sqm2 to be an excellent benchmark for most bog standard domestic extensions.

Bear in mind that in London £1000 may just be the starting figure for basic finish. I've looked back at my quote and I'll actually be paying £1200/sqm2 but that EXCLUDES windows and heating (as I want somebody else to do these). My extension will be 14m by 3.6m.

You may get a little below the £1000 mark but I wouldn't bank on it.If you do get estimates below thisvalue then do come back and tell us, I'd be interested to know

 

[DeludedAussie]

You won't actually be charged by the metre as such but on average it costs about £1000/m2 for extensions. The builder has to price in stuff like electrics, heating, windows etc

Though people on here don't like to give 'estimates' over the internet because of all the unknowns I have found the £1000/sqm2 to be an excellent benchmark for most bog standard domestic extensions.

Bear in mind that in London £1000 may just be the starting figure for basic finish. I've looked back at my quote and I'll actually be paying £1200/sqm2 but that EXCLUDES windows and heating (as I want somebody else to do these). My extension will be 14m by 3.6m.

You may get a little below the £1000 mark but I wouldn't bank on it.If you do get estimates below thisvalue then do come back and tell us, I'd be interested to know

Can I just make sure I understand this - You are building a 3.6 by 14 metre extension (50 sqaure metres odd) so the shell is going to cost you 50K??

I find this difficult to believe

Yes you will need a bit more material but the biggest cost of an extension if the foundations and digging and for 50Sq M I would be shocked if you could not get that done for 30K shell standard

 

[limerockconstruction]

No - £1000 covers internal finishing as well, paint skim elecs (in my case mentioned above kitchen too)

 

[indus]

You won't actually be charged by the metre as such but on average it costs about £1000/m2 for extensions. The builder has to price in stuff like electrics, heating, windows etc

Though people on here don't like to give 'estimates' over the internet because of all the unknowns I have found the £1000/sqm2 to be an excellent benchmark for most bog standard domestic extensions.

Bear in mind that in London £1000 may just be the starting figure for basic finish. I've looked back at my quote and I'll actually be paying £1200/sqm2 but that EXCLUDES windows and heating (as I want somebody else to do these). My extension will be 14m by 3.6m.

You may get a little below the £1000 mark but I wouldn't bank on it.If you do get estimates below thisvalue then do come back and tell us, I'd be interested to know

Can I just make sure I understand this - You are building a 3.6 by 14 metre extension (50 sqaure metres odd) so the shell is going to cost you 50K??

I find this difficult to believe

Yes you will need a bit more material but the biggest cost of an extension if the foundations and digging and for 50Sq M I would be shocked if you could not get that done for 30K shell standard

Who said anything about a shell? The op mentioned the job being plastered and finished, so that would include glazing, electrics, heating and perhaps a bathroom.

I'm paying over the £1000 mark but it doesn't include windows and heating. However it will include expensive brick (to match existing), expensive roof tiles, insertion of about 6 RSJ beams where the extension opens into the existing house, the creation of two bathrooms, the fitting and tiling of two bathrooms, god only knows how many spot lights and sockets.

As well as that it is a period house and so there will be external timber (soffits, fascia etc) that needs to be made bespoke to match existing. Internal timber ie architraves, skirting boards that need the same.

Finally there is coving, fibrous plastering etc that again needs to be made bespoke to match existing.

So these are the things that push you above the £1000 mark (in London anyway). Could you have a shell built for the £600/sqm2 you mentioned? Perhaps, I don't know, as I'm not a builder and have only ever had a 'finished' extensions built.

 

[noseall]

the biggest cost of an extension is the foundations and digging

Says who?