Idea of cost for double storey extension!

[RoseGoldEagle]

We’re planning a 24 metre sq. double storey extension (8 by 3 metres) and am trying to get an idea of costs to know if it’s possible for us to afford it. My calculation so far…

£2000/metre sq for ground floor: £48,000
50% of that for first floor £24,000
=£72,000

The ground floor will be one big room (will need to add new kitchen which have budgeted for separately) but the upstairs will be a new bedroom with en-suite, plus an ensuite for an existing bedroom. Do I need to add more on for the upstairs- given it’s not ‘one space’ (I don’t mean to actually kit out the en-suites, am just meaning the actual building costs)

If anyone has any rough ideas how much extra I should budget for that, or if the above seems realistic, I’d be very grateful!! Thanks.

i am doing a one story wrap around extension (hopefully).

its 5m by 2.5m at the back and 4m by 2m at the side. I have been told that will cost about £50k. This doesn’t include flooring or kitchen. Just the shell.

there Will be additional plumbing costs for yours upstairs - extra stud walls aren’t expensive. The plumbing costs will depend on where existing pipes are - I think sewage is the one that can get expensive.

sprry this probably wasn’t much help.

@Mellowyellow222 we’ve just done a very similar extension (2x5 side, 4x4 back) and it was £100k. No kitchen, but did include a bathroom. That included groundworks as well as windows, doors and painting. We’re in the SE.

We were quoted £55k which is why I was so surprised by the final cost!

@sarahb083 that has terrified me!!! I am in a much cheaper area - but Witt cost increases I could be in for a shock!!

did you take down side and back walls?

I am terrified how much the kitchen will cost on top of all this!!

Hmm we are doing the same size double storey extension + garage conversion. We are also doing rewiring, some remodelling inside and new windows. £200K.

Two story 3x 12m ish shell was 75k. Roof, windows and doors. A lot of it was cash in hand at the end so add some more on for vat. We ran out of cash!

3 rooms downstairs and 3 upstairs.

Will you need a bigger boiler? The plumbing for upstairs will add more. Will you need new soil pipes from upstairs or need to move existing pipes? We had to add a new drain.

Ours was two years ago, and 4x+10m double storey, so a little larger, and was £110k excluding any decorating costs (we painted inside and out ourselves). We spent more on top as we replaced all the windows and doors in the existing house at the same time.

Is 3m the outside width or internal? Outside walls are about 30cm. It might be a little tight for a bedroom if you think of the length of the bed and space to walk past the end of it. Should be okay but you won't have space for wardrobe or chest of drawers at the end of the bed. I'd measure out the internal space and the size of your furniture to plan layout first.

Got to be at least £100k considering what I'm hearing from friends having work done

We’ve been talking to architects recently and from informal chats we were told £3k per sq metre. And realistically looking at £300-£400k for double storey all in, fully finished.
A friend round the corner from us has just had 2 quotes of £150k (cash in hand so no VAT 😬) and £230k for a single storey wraparound extension.
Absolutely eye watering! 😫
We’re in SWHerts.

I would say £150,000 to £180,000 at least to get it finished.

I see tax evasion is still going string in the building industry. Don’t we need to pay tax to support the NHS?

I've also been told recently £3k per sqm. I'm in Manchester. That's build only to include plaster finish & electrics.

I don’t think they can get away with a major tax dodge as the builders quote you first. We was quoted 75k including tax. Things went wrong and the overspend ( about 3k I think for foundation issues) partly came off the tax. These things never stay on budget and we had no more money. If was to do it again I wouldn’t unless I had 125% of the quote up front. You have no idea what will go wrong that’s beyond your control. There are points at which you can pause and save but floors in with no roof isn’t a good idea to leave for a long time.

I don’t think you can reduce by 50% for the first floor extension. It’s a myth. It’s true you won’t need more foundations, but there will be other costs (eg designing the timber frame, paying for more scaffolding).

I don’t know what are the prices where you are (I’m in SW London where everything is expensive). But I would budget £3k per metre, which for 48 square metres is roughly 145k.

Then add 20% on top for VAT. You’re now at 175k.

Also consider items such as glazing - are you planning any special windows, such as oriel or large sliding doors? Just the sliding doors can cost 10,000 or more. This won’t be included in your initial 145k.

Will you need to do any work on your existing house? New plumbing, wiring? Energy measures such as new insulation? Solar panels? That’s on top.

Are you planning any joinery? Joinery is eyewateringly expensive. Built in wardrobes easily run into several thousands. That’s per room, not for the whole house.

Will you need new furniture? Flooring? Etc etc.

You also need a budget for unforeseen circumstances. I’d say at least 20k but could easily be more.

You will need to completely redo your garden at the end, lay new lawn, possibly new paving.

And don’t forget about all the other professionals. Even if you don’t hire an architect, you will need a structural engineer (a few £k), a planning application (at least a few hundreds, probably more), possibly a party wall surveyor? Building regulations. Architect or technician fees. Project management. All of this adds to many, many thousands more.

I’m sorry for being blunt. I’m currently doing a pretty large extension (adding approximately 100 square metres on three floors, so garage conversion plus two floors on top, plus other extensions and garden room) and the costs are so far off the oft-quoted 3000 per sqm mark, that I would rather warn you. Unless you have mates’ rates, or are able to design and build it yourself, I wouldn’t attempt it on your budget.

huh? You are surprised by this? I am surprised that you are surprised. This is absolutely the norm.

OP, double your quote and add 10% to get it finished.

Unless you want your builder to be an absolute crook, budget to include the VAT.

I am mid build and think £3K/msq is too low as well if you need electrical and plumbing work. The finish you’re looking for will dictate the cost too. Unless you want to be very cheap, things like vanity units cost hundreds. Sliding doors are thousands. Kitchen appliances are very slow and again can be hundreds.

If you were in London, I’d say about £120K if you’re not doing other renovation work.

To clarify do you mean 3x4 on 2 stories so 24 sq/m in total or 48 sq/m in total? My estimate of 120k is based on 24 sq/m and no other work.

@Mellowyellow222 No, we didn't knock down side and back walls - we knocked through a window at the back and turned it into a doorway, and at the side we knocked through the existing side door - so no steels needed.

We did a similar build, and budgeted £100k for that and £50k to build a garage and some other work. The total has come in nearer £200k.

I would say £120k-£150k.

😳. It gets worse! I really need to rethink my budget

Ours just completed cost £250k but we did get a £160k quote too. Very expensive area to build in though and high spec wiring and roof lights.

Simple single story extension to the back 8f my bungalow, rsj to support as wall to cone down between current conservatory and kitchen to make a larger open plan kitchen/living area, 55K plus vat and that's with my son doing the brickworks. Only includes groundworks/footings build, roof, upstand glass skylight, plaster....electrics, plumbing and new kitchen and decorating and making good inside to add on to that. Realistically 75K, it's actually cheaper to move to a bigger property.

We did a similar one and it was £60k ish, not including all the fittings for the ensuite and kitchen. And that was nine years ago! We’d been led to believe it would be £35k…

Thanks so much everyone, this is incredibly useful! Reality check time I think!