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Surprise costs in a house extension?

(26 Posts)
ThisOneNoThatOne Sat 27-Aug-16 19:35:56

I'm trying to work out a realistic cost of our extension. We have a 1930's 3 bed semi and we're hoping to have a single story extension at the back of the house and a double story at the side.

The quantity surveyor has sent through a comprehensive breakdown of the costs. It seems to cover most things, apart from kitchens, bathrooms & decorations.

I was wondering if anyone had any hidden costs that you hadn't been prepared for. Eg portaloos, digging deeper foundations etc and how much extra it cost you?

Thank you!

RatherBeIndoors Sat 27-Aug-16 21:36:32

I am please God nearing the end of a single storey extension. I believe we must be at optimum dust levels now. Agh. The unexpected costs so far have been manageable: additional lintels when removing windows when knocking through and surprise there were no supports at key points in the wall; also we'd hoped to re-use the glazed back door and two windows. The building inspector said they were no longer up to code so couldn't be re-installed anywhere else and we had to buy new ones. Ho hum. But if that turns out to be our biggest problem, I guess I'll be feeling lucky!

Re portaloos - for you? Hopefully you won't be left without a working toilet overnight at any point. We have been spending as much of each day out of the house as possible, and shamelessly abusing the goodwill of friends and family grin The builders do not seem to ever need toilet breaks, which may be connected to the fact that they firmly refuse all offers of tea/coffee/liquids!

LadySpratt Sat 27-Aug-16 21:51:27

The only unexpected cost was our neighbours exercising their right to an independent party wall surveyor who scrutinised every bloody bit of our architect drawings. He fancied them not detailed enough so our chap turns over some new drawings overnight and sends them off. 10 working days later we receive a reply asking for more. So the cycle repeated itself twice more. Ultimately no changes were made to our drawings, it added 6 weeks to the build (our builders were fabulously on track before this), and I had to incur the extra costs of three sets of architect's drawings and party wall surveyor fees which came to the tune of £10k.
All involved in our house felt the neighbours just did it because they were miffed that we were extending so displayed it by being nasty and to hit us in the wallet. angry
Neighbour envy. Not priceless.

Toomanycats99 Sat 27-Aug-16 22:08:30

Ours was loft not extension but things like if you are having a new bathroom is your boiler powerful enough and if you are having anew boiler how big are your gas pipes and will you need new ones fitting. We had to compromise on the boiler as our too small pipes were under the concrete floor kitchen extension!

And yes party wall surveys. Ours came in at £1.7k.

Autumnchill Sat 27-Aug-16 22:11:17

Skips! Never under estimate how much these cost!

ThisOneNoThatOne Sat 27-Aug-16 22:22:40

Thanks for your replies. Some of these don't seem so bad!

I've already included the boiler costs, however I haven't thought about the pipes, so thanks for that info.

autumchill how much were your skips?

I think we will be left without a working toilet, as we're moving the bathroom. We are planning to move out- yet more costs!

Gosh £10k! I hope my neighbours are more accommodating than yours ladyspratt!

Toomanycats99 Sat 27-Aug-16 22:33:30

Yes - apparently most modern boilers require 22mm pipes. Ours left gas meter at 22 arrived at boiler at 15mm Meter at very front of house boiler at back with no idea where they changed!

namechangedtoday15 Sun 28-Aug-16 00:03:09

Just coming to the end of a double storey extension of a 1930s semi. Additional costs came from having particular roof tiles (more expensive than usual), having to move loft hatch, electrics costing more than double, more plastering when cracks were revealed after taking massive built in wardrobes out, front and back gardens being trashed, storage costs. Then the costs have increased as a result of not being prepared to scrimp / go basic once the space started to take shape (when I'd included estimates for budget options), paying for decorators after realising it was a much bigger job than we'd anticipated and replacing flooring / decorating the rest of the house that looks tatty after being a building site for 6 months.

Ntinyn Sun 28-Aug-16 06:28:15

3 weeks into single story 1930s extension, additional costs so far- pest control to remove live wasp nest, back garden trashed so will have to sort that out when they leave. They're still outside though, coming in next week.

alibobs Sun 28-Aug-16 07:06:38

Our builders have hired a portaloo for them! they didn't want to bring dust in as we only have an upstairs bathroom at present.
We are 3 weeks into a single storey back and side extension and so far the only extra cost has been the foundations at the side due to the neighbours Ash tree. The builders made us aware of this at the point of quoting. It cost an extra £300. We were told to have an extra 10% of the build cost as backup.
Extra costs for us so far are changing our minds on kitchen, flooring and all the pretties! build cost so far is spot on (fingers crossed!)
As for skips our guys used a grab lorry so just piled up the earth etc on the front garden which needs doing anyway and that worked out cheaper than a skip.

Buscake Sun 28-Aug-16 07:10:49

1930s semi side and back single storey extension here. Biggest additional cost was having to get piling done for foundations 😱 We had suspected it would be necessary and we got a bargain price (still about £4k if I remember correctly)

LadySpratt Sun 28-Aug-16 08:44:32

It wasn't all bad OP, I stuck it on the credit card and got some store vouchers to spend on the interior! However, years later I still can't get that taste out of my mouth, even though we're very civil on the surface.

grannycake Sun 28-Aug-16 11:04:55

Not an extension as such. New boiler and new bathroom in existing 1930s extension. Originally £9500 excluding tiles we have had several unexpected problem - needed new joists and lintels and also needed to tank utility room and replaster.. As the work has dragged on with each problem we also decided to install a toilet in utility - just as well as 4 weeks in and still no bathroom. Also have spent £££ on rubbish removal. At the moment it looks like we will be paying an extra £3500.

flummoxedlummox Sun 28-Aug-16 12:33:25

Just finishing a single storey rear extension and the additional costs over the original quote were £1600 for deeper foundation due to a tree, £2500 to build a patio (which we are well pleased with) and £260 to treat an area of the original joists that had woodworm.

ThisOneNoThatOne Sun 28-Aug-16 12:38:56

Thanks all

grannycake what was the reason for needed new joists and lintels?

Autumnchill Sun 28-Aug-16 13:18:45

Our skips averaged from £180 - £300 and even with getting a few free through contacts at work, we spent £3k.

We are renovating a 1950 semi which needed completely gutting and new electrics / central heating plus we've done a very large double storey extension at the back and a single side storey and we are up to £80k with minor decorating and major garden overhaul left to do. This price includes kitchen and 2 new bathrooms so build costs were probably about £65k and we did quite a bit ourselves as we are both in construction so could get mini diggers etc to do our own footings. I would do it all again though, absolutely love doing it and looking back at what we've achieved to build our forever home near the beach smile

Just taking a break from clearing out the front room which has become a junk room. Back to it!

grannycake Sun 28-Aug-16 16:33:32

When they removed the plaster the downstairs window had a rotten window lintel and the door into extension didn't have any lintel at all. The joists under the bathroom floor were rotten - probably a small leak over many years. The house is late nineteenth century and the extension seems to be 1930s. The joys of an old house!

Ntinyn Sun 28-Aug-16 19:42:48

Oh and just thought, i think these extra costs we're due to us not budgeting properly rather than a fault of the build, but we didn't factor in the cost to dig and rebuild a patio area (we asked builders to carefully remove the existing patio and decking so we have option to re use) as well as temporary kitchen costs. Our builders offered to set us up with a makeshift kitchen but their hob and sink unit took up too much space in our small lounge which is the only usable downstairs room so I've purchased a plug in electric table top hob and decided to make my life being pregnant and full time caring for my toddler even harder by washing everything up in upstairs bathroom sink.

MiaowTheCat Mon 29-Aug-16 08:35:22

A new hoover - ours never did recover from the dust bombardment - even after the builders had tried their best to clear up the initial mess.

We're doing bits in stages to a late 1920s - big issues we're finding are just that no walls are ever bloody straight which seems to add to timescales (and builders' blood pressure) and the fact that even in the rest of the house the plasterwork is getting to be shot to hell anyway and faffing about with building work seems to be working loads more loose than we were initially anticipating.

Apart from that - I was anticipating damp hell when they took things like our kitchen out and the walls were really really solid and dry!

Doesn't really affect what we're having done here but I know we've got a sewer running under the back garden which could impact on any future extension work I guess.

We've also needed a new consumer unit for the electricity and if your house is anything like ours of a similar age - as rooms have been getting turned upside down there's been an element of "aah fuck it while it's chaos let's get loads more electric sockets fitted in as well" which adds to the costs.

PurpleWithRed Mon 29-Aug-16 08:50:27

The first unexpected cost for our self-build came on Job 1 day 1 when the building regs bloke came to watch the foundations being laid. The trial pits had indicated 1.5m so we'd timed and budgeted for 2m but we hadn't been there to supervise the pits being dug and they were done in the wrong place (Mistake #1 of many). Ended up with 3m deep in some places. Just had to stand and watch as the Building Regs said "nope, that's still sand, deeper" and the PM ordered another lorryload of concrete.

IMHO you can plan till you're blue in the face but there will be unexpected extra costs so you need a decent contingency fund.

Ntinyn Mon 29-Aug-16 08:54:32

Oh yes to a new vacuum! I was thinking yesterday that our old Dyson is packing up from the dust. Or maybe I just need to clean all the filters. Yawn.

Autumnchill Mon 29-Aug-16 13:27:23

Yep to a new Hoover! Ours couldn't cope with the dust that you get for months after!

Clankboing Mon 29-Aug-16 13:32:46

Keeping things in a storage unit for months - grrr.

Ntinyn Tue 06-Sep-16 17:58:11

New cost that has come up today... Builder had to move our sky dish to build our new flat roof. Now no sky signal and since we don't pay for their insurance, have to pay engineer call out fee (or pay for sky's maintenance contract). In any case, it's really annoying as we only had an engineer here a few months ago (paid a fee then too) when we moved in to reconnect us and wish we had the forethought about the dish positioning!!

Loumate666 Tue 06-Sep-16 18:22:48

A few potential 'gotchas':

- Moving Services - Telephone, Gas, electricity & water (worth considering upgrading the supply pipe if yours is old
- Boxing things in - pipes, electricity fuse boards
- Loft hatch / eaves access
- Filling holes, cracks and gaps before decorating
- number of electrical sockets
- Specification of things - doors, skirting, hinges, fire doors, e.g. you say you want 'x', the builder says 'I've only included costs for 'y''
- driveway
- external steps / retaining walls
-in a nutshell, if it's not on your plans, they will charge for it unless love managed to specifically include it in your agreement


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