How do I estimate the costs of an extension?

[wywywywy]

Hi all,

Basically I am looking to buy a house, in an area that I really like. There is a problem however, the houses in that area are pretty small, usually 2-bed semi-detaches.

So, if I buy a house there, I may need an extension.

There is one for sale at the moment, which is in a corner plot position with an attached garage. The extenstion I want to have would be a 2-story one - to the side it will have a small bedroom above the garage, to the back the ground floor will extend the kitchen space, and to the back the first floor will extend the master bedroom massively (may be an en suite as well).

The problem is, I do not know how to roughly estimate the price. I mean, is it going to be 10k? 20k? 30k? 40k?

Is there any sort of guide price with extensions? Like £ per square metre, what roof will add how many %, what rendering will add how many %, how much to budget for per window, how much to budget for for the en suite, etc.

I haven't bought a house yet, so I can't just get the builders around for quotes, plus I don't know which house I am buying. So ideally what I would like is next time I go see a house, I can have the ability to tell myself, "Hmm, this will cost me about 20 grand to do an extension."

Please enlighten me!

Thanks.

 

[masona]

Is there any sort of guide price with extensions? Like £ per square metre,

Yes there is, used to be per square foot, I'm not up to date on the latest price but others here may know. A quick phone to the BCO may tell you roughly in your area or any architect in the yellow pages may help.

 

[jeds]

The current rough estimate is £1200 per m² super. Depends on build quality, where you are in the country, access to the site and any special features, fixtures, finishes etc. Foundation and drainage arrangements are also primary factors.

 

[wywywywy]

Hi,

Thanks! But that leads me to another question - if it is a double-story extension, I would guess the price per square metre would be lower? Is that a correct assumption? Because the foundation and the roof only apply once if you know what I mean.

And also... hmm... is the North West generally more, or less, expensive than the rest of the country (excluding London) in terms of tradesman labour charges?

Thanks.

 

[jono_h]

I worked to £1200m3 for the first floor, and £800 for the second floor (first floor is more expensive because it accounts for the roof)

Architect / Builders etc all thought my estimate was pretty close based on the above, and having completed 2/3's of the build I look like only being a few % out.

Be warned though - it does all depend on the level of finsih. The finest italian marble flooring, or multi-jet steam showers will make this figure wildly inaccurate.

 

[NS215]

the m3 price does this include the loft space or do you just do the size of the rooms and does the ground floor figure include a standard depth footing????

 

[wywywywy]

Metre cube of air space? Or metre square of floor space? :O