30sq/m extension over 2 floors, any know a rough cost? £45k-ish?

[sugarhoops]

Title says it all really - based on the £1500 per sq/m our architect gave us, it'll cost around £45k, which seems almost too reasonable to be true if I'm honest (we're in Wiltshire, so not too costly an area).

We're not needing a new kitchen or any new bathrooms - its literally doubling the size of current kitchen (knocking out a door and window to join the 2 together), plus an upstairs bedroom. Also need to factor in bi-fold doors cost, but our architect put those on his own house recently and told us his bi-folds cost £4.5k, so not the hideous £8k-£10k I thought they might cost.

Anyone willing to shatter my dream that we might just be able to do this for under £50k?!!

Our bifolds cost 1800 plus a couple of hundred to fit. They're only engineered softwood, but look a million times nicer than the UPVC ones we were quoted for. Our two storey extension is about twice that and cost around 80k, not including fit out, but including plastering and skirting and some painting.

Thanks mummytomog - so the £80k is just build cost then? do you know how much space you added overall?

It all does depend how smoothly things run. Foundations can be as easy as pie or a nightmare. Ours were much deeper than we thought they would be, our house is modern, built on a slope and so is on a concrete raft foundation.

They kept digging and digging and digging to try to find the concrete raft, so much so that we started to doubt the raft! But we have no air bricks so we have to be on solid foundations.

That did cost a teeny bit extra than we thought (less than £500) but we came in pretty much on budget (single storey though)

So anything such as re-routing pipes/drains/electric cables/gas pipes etc can all add up. But if straightforward then it's fairly simple.

It's a bit of luck and an amazing builder!

Thunder we priced all our stuff up separately, so build was one lot of costing, kitchen units another, appliances etc It meant we knew that pretty much everything except the build part was a guaranteed price.

We have still to have a glass splashback installed in the kitchen but we sacrificed that and under cab lighting to landscape the garden instead.

We paid £30k about 8 years ago, including bi-fold doors and a complete re-roof of the whole house.

We added on just under 60sqm and changed the purpose of the old kitchen and bathroom (both have become useful hallway/landing areas). Had a few RSJs, a buildover a sewer pipe, slightly deeper foundations as we have a lot of trees and some fannying about knocking down the old garage and 'conservatory'. We ended up about 5k over build budget on some rotten floorboards, extra wiring and consumer unit and a few other bits and pieces.

The budget is about right for building costs. To that you will need to add:

1. Fees: planning / building control, measurement surveys, engineer drawings, Thameswater (if you are building near or over any drains in your back yard) and your architect fees. This can easily be an additional 8K-10k on top of building costs
2. Costs of re-landscaping your garden: I would budget at least 5k as you will need to do all of your landscaping / lawn etc
3. Fit out: you will need to budget for new flooring and lighting. You should think about if you will need new flooring in the adjoining areas as well. While the 1,500 psm cost quoted will include fitting new light fixtures it most likely will not include the costs of new light fixtures. You will also need new skirting. The costs of these are like how long is a piece of string. It really depends entirely on what you choose but the flooring and lighting as a minimum will be at least 2k but easily could be much more than that.
4. Budgeting 1.5k per linear meter of bifold door will get you good quality but again, these can be a lot more. If you want extra-wide glass to reduce the number of leaves or if you want ultra thin sightlines or doors taller than circa 2m then expect to pay more
5. What kind of windows are you putting in? If you want timber sash windows, budget 1.5k per window. If you want veluxes anywhere in the house, budget 500 GBP per window.
6. Add a 10 to 15% contingency for unforeseen events. It might not be necessary but it should always be part of your budget.

So the long and short of it is including all your fees, re-doing your garden, flooring and lighting, bi-fold doors, windows and contingency I would add around 25k-30k on top of the quoted build costs for 45k. All in, I would say you are looking at 70-75k for the extension you describe. Sounds lovely though!

Why would you need to re-landscape your whole garden?

We are turfing our garden in Oct and building work will start next spring to build a single storey back extension. We are leaving the patio are which is 3m deep as hardcore and will lay the patio when the build is done.

Is this a bad move? Might the rest of the garden get damaged?

Sorry to hijack OP!

The builders will ruin your garden. Absolutely do not lay new turf ahead of major building work!

If your garden is huge you probably won't have to returf the entire thing but the bits nearest to the house will be a mess.

Thanks all - yes londongirl, I take your point re: additional costs, but like nikki i don't think i'll need to spend £5k re-landscaping (I hope!). Bi-folds we've been quoted just under £5k for some lovely ones, we're using my friends husband who is an architectural technician - will be around £1k total. Plus another friends DH is an electrician and has said he will do electrics for us- should be a v simple job looking at plans.

Using your very helpful list though, i've totted up and I reckon it should be nearer £60-£70k, which I think we can do with help from parents loaning some £££.

Gosh, I might start a spreadsheet itemising everything [geek accountant emoticon]

Thanks all

Eek. How far out from the house would you say they muck up?

20ft at least depending on what needs to be done. They leave a lot of the materials and machinery outback as well as run new drainage connections as necessary. As you aren't having any foundation work done then it might not be so bad. Most people need to re-turf at least in part of the way though and lay a new deck.

Sugarhoops, definitely make a spreadsheet. Its all the little things that add up!

Our back garden was completely and utterly destroyed. I could show you a picture, but it would totally out me! Basically we are putting a deck over the worst of it (costing about 1k and we are doing most of the work ourselves) which is 3m out from the back of the house. They also dug massive holes in our garden for no readily apparent reason, then filled them back in with hardcore, which we had to top up with top soil and then returf. and they left loads of crap like drainage pipes, scaffolding, tarps, the old bath etc lying around. They also knackered the drive, so we're paying a few hundred to get some tarmac lifted and relaid.

We had to pay Thames Water off, and it was only about 400. Our building control costs were 700 or so. PP was about the same. Skirting was included in the build/plastering costs, we just levered it off, laid the floor and then stuck it back on again. Was a no brainer. Also meant we could undercoat and gloss it while it was off the walls, which was handy.

Flooring, if you do it yourself, can be a bit cheaper. We did 30 sqm downstairs for about 450 quid in a niceish laminate from B and Q (collaris harlech oak narrow if you're interested) with fibreboard underlay to keep out the chill. We did the upstairs rooms for about the same in carpet (bedrooms) and vinyl tiles (gerflor, and around 7 quid a metre in the bathrooms. Black and white look particularly good in a chequerboard). Our lighting was not expensive - Ikea ceiling lamps were about 30 each in the hallways for a nice general light, a big spot bar in one end of the kitchen diner for 40 from Ikea and then I bought a lovely pendant in the Habitat sale for the kitchen. The electrician had left single pendant bulbs, so it was the work of about ten minutes a light to swap them over. Put Pendel pendants from Habitat everywhere else (a tenner I think) and bought cheapish drum shades from Ikea.

This is the extension Ikea built. I should be slightly ashamed, but it looks farking awesome and I haven't even finished it yet. I will reiterate however that even with all the cost cutting and budgeting and doing stuff myself and sourcing things as cheaply as possible, we went massively overbudget. That contingency will be really really important. In one sense we can't complain that we've managed to build a big extension and convert the loft, completely rewire the house, add three bathrooms, a new kitchen and a utility for 140k or so, but when I add up the costs, I do want to weep. We thought we would do it for 110k. Ha.

We were told to work to £1k per sq m per storey, so £60k.

See your extension mummytomog is double the size of ours (ours is 30sq/m compared to your 60sq/m), so I'm thinking that halving your actual cost of £140k makes ours a potential £70k....plus we don't need any new bathrooms /rewiring / new kitchen etc.

I'm starting that spreadsheet now - some v helpful advice on here, many thanks. Plus enjoying my gorgeous landscaped garden before it gets trashed by builders next summer

Mummytog, getting all of that done for 140k is massively impressive even doing work yourself and using Ikea!
Everyones garden looks like a bombsite after the work is done and it is one thing most people forget to budget for.

You end up with a beautiful extension with floor to ceiling glass doors and a panoramic view of what looks like a warzone until you find the money and the energy to sort it out!

Out builders haven't really knackered our garden too badly We have nearly completed our single storey extension and only about 2 feet of grass are bald. We had a new deck as part of the job and this covers up the worst bit. I have been keeping tally on a spreadsheet and ours has cost about £75k including the kitchen.

How big is your single storey marmite, out of interest?
Ours sounds really small at only 30sq/m over 2 floors, but when I stand outside and look at the space it'll fill, it seems massive. So everyone else's on here must be really massive!

Not sure! New floor was 59m square but that includes smallish hallway and remodelled kitchen and dining room as well as extension...

Ok thanks marmite - this thread, whilst making me realise there are lots of bits and pieces I need to consider, is giving me some hope that we might be able to do ours for around the £60k mark as its not massive and is literally just building, heating, lighting, flooring with no added extras such as new kitchens & bathrooms