Any ideas how much this extension might cost?

20 May 2010
Reaction score
United Kingdom
Hi All,

I'm thinking about getting an extension done and just wondering whether it's in my budget or not. Also, I'd appreciate your thoughts on my overall idea - in case there's something you think could be done better.

Here's the current layout - it's the basement which backs onto the garden (two storey from the front, 3 at the back). There's a side galley then the next doors house. Where it says wall - that's a thick stone wall separating my garden and the neighbours garden.


Here's what I'd like to extend it out to:


And here's a photo of what the kitchen/dining area would look like:


I'd like to knock the whole 'old' extension down (which is the last block in pic one) It's an old two storey extension with very thick walls and it is always freezing there. Currently it's the kitchen and a bathroom above it. I'd like the 1st floor to extend out as far as the kitchen to make a bedroom. Then on top of that, to extend the 2nd floor enough to put a small-ish bathroom as that's where the 3 bedrooms are. If budget became an issue I wouldn't mind if these two rooms are just plumbed with electrics as the plaster and finishing can always be done another year.

So what do you think? Any rough estimates on what this might cost? Could anything be done better? Any thoughts at all?

Thanks in advance!
Sponsored Links
Hmm.. kinda vague on the details.. so expect kinda vague estimates.. could vary by 10s of thousands..

So lets see if ive got this correct.. 2 storey terrace? with basement starting mid property to rear.. rear room was extension to classic 2 up 2 down with cellar.. but was continued up to 2nd floor..

Now you feel the walls are a little thick so wanna rip down the whole 3 storey extension to rear and replace.. if this is a semi-underground structure to get the walls any thinner you will probably need to go reinforced concrete in the basement area, which will also assist with the cold/damp but puts the price up massively..

Demolishion of the rear of a property especially a terrace is a nightmare on moving materials and general site access.. assuming you wont be habiting the property for the 3 months of build this wouldnt be such an issue..

So you put back the extension on the original footprint to save a few ££ on foundations and party wall awards as well as planning etc and then remove the two internal massively load bearing walls in the basement area and put in a couple of framed steels with indepentant pads..

Then after doing all the finishing touches the kitchen which to be honest looks like about 20k's worth of gear arrives and is fitted.. job done..

Hmm rough price.. well.. worst case scenerio if all the above happen then probably around 120k for a city centre location.. but to be honest that could go up by 30k if foundations arent suitable to modern building regs.

Hope you have deep pockets..
Its not very clear from your plans but you'll likely have problems getting building regs approval unless your stairs have direct access to the outside via a protected (fire proof) corridor/room. ie you won't be able to have it completely open plan.
Your basement is cold and probably damp because its underground whatever you put back in its place will also be cold.. unless you can channel some sunlight underground..

You may want to consider some more econmical solution.. rather than rip things down because they are "old"..

Might want to consider under floor heating in the basement area.. and not make it so open plan which will make it colder in the end
Sponsored Links
Thanks for the replies both, and sorry for not being clearer.

The houses were originally normal two storey houses with basements from what I gather, but then I guess they got two story extensions and basement rooms as all the houses in this row are pretty much the same - although some extensions come out further than others, and some are 3 storey.

When I rang the council they said they were pretty open as the houses here have a range of different extensions, also, there's a great big pub on the one side which I think goes in our favour too (?)

Here's a photo from the back, my house is the one on the right - you can see the two storey extension at the back which is the kitchen on the bottom and bathroom above it.



Here's the front of the house (middle):


And here's a photo of the basment room, looking into the kitchen and showing the stairs going up:


That's the room I planned for the lounge area. The neighbour already has their basement open plan - so I guess the council won't object.

What do you think? If you need any more info just ask.
I've quickly added some doors to this pic so you get a better idea of what I mean too:

I gotta be honest I'm not entirely sure of the existing layout of your house and what the proposed is. It is rather hot where I am in my defence! :p

Anyhoo. A rough cost of building extensions is around £900 per m2 per floor. So work out how many m2 you intend building from scratch and X it by £900. As you are demolishing the old you will need to add a bit on for this. As Static implied if you're going for a very high spec finish/kitchen etc you can expect the figures quoted to increase.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links