House Extension - extra costs please

[mynameischloe]

We are planning a single story extension, currently early stages.

We are obtaining quotes for the work and I am making a list of all the extra costs we need to consider outside of the building work. So far I have:

Flooring costs (also would need to re-floor the old part of the house to match the new)
Decorating
Blinds/curtains
New dining table and chairs
Small sofa and new TV for small sitting area
Radiators/heating
Any new interior doors

What am I missing please? DH thinks we can stretch to a larger extension... but I want to show him how much everything else will cost which will push us out of budget.

Plus a contingency of 10% and then some more!

Thank you.

Light fittings
Any electrical or plumbing work that isn't included?

Ooh yes perfect, thank you.

Just thought - cost of moving gas box if applicable.

And another one - the cost of installing a new boiler as ours is on its last legs so we're going to install a new one at the same time.

We are in a similar position and, following advice on previous threads, I put together a spreadsheet and costed up the additional items down to the last light switch and door handle. It was eye-opening - about 50% on top of the builders quotes.

Obviously this depends what you’re having done - ours includes new kitchen, new flooring in almost the whole ground floor, new downstairs WC, new sofas, furniture etc etc. So it was definitely a helpful reality check before we confirm the scope of our build!

Exactly @MsShopper

I'm trying to tell DH that if a builder quotes £50k it's going to end up being around 75k. I'd rather have smaller extension with better fittings/fixtures/furniture etc than a massive extension and sitting with bare floors and walls because we can't afford to finish the job!

For us an unfactored cost was the drive being ruined and landscaping. I stupidly thought the drive would survive the job etc it didn't. The neighbours fence next to the extension really needed a new retaining wall too.

Thank you. DH already said half the lawn is going to be ruined, so how on earth are we going to pay for new turf etc to be laid if the budget has all gone.

I'll add that to the list.

Depends on your builder and quote, we've received quotes that have been itemised down to the number of lights switches and plug sockets as well as painting everything, about 4 page long quotes. While that won't include actually filling the space with furniture, lightshades and curtains etc. it's given us a good idea of overall price

Depends on what is included in the builder's quote. We were quoted just under £100k for a first floor extension and ended up just £1k over. The £1k is because we wanted our water cylinder changed. The quote included plumbing, electrics, tiling, flooring and decorating, all itemised including allowance. (For example tiling half height in bathroom for tile of certain sizes, LVT click flooring, number of switches in rooms).

I see that you have allowed for re-landscaping. That will definitely be out of a builder's quote.

I am so pleased you posted this I am in exactly the same position. My question is, where are you going to get these prices? Are you guesstimating them?!

Things on my list so far:

Windows
External Doors
Kitchen fittings
Kitchen Table/Chairs
Flooring
Bathroom Suite and fitting
New Boiler
External Cladding
Underfloor heating and/or rads
Architect Fees (these have added up to a lot!!)
New Garden Decking
New Garden Furniture
Re-Landscaping (hadn't thought of that until I read this, no idea how much it would cost though!?)
Electricians Bill and Electrical Fittings
Paint

My problem is I am now just guessing them which is naughty and sort of negates the point. Is there some magic resource out there I am not tapping? (I mean other than the internet!!!!) I sort of expected there to be this handy guide out there ha ha like an idiots guide to building an extension!!!!!!!!

Yes, the architect and all the extras which go along with that are expensive. Lots of sets of drawings, building regulations etc. I think it will add up to around £2k.

I guess it would be a case of ringing all these companies to see how much things would cost! I really don't want to under estimate.

Good point ref asking the builder exactly what their quote would cover.

We had a rear back and side extension last year. I would add extra lighting outside. Outdoor plugs and we ended up changing internal doors so everything matched. Cheaper to tack extras onto the main build than start a new job.

You'll end up getting the garden redone too

@mynameischloe you are so right a day on the telephone is in order! Good luck with your planning!

Our big over spend were plastering and electrics. DH went mad with amount of sockets and we had top end lighting via a designer. Looks great but it does cost!

When we had our extension quoted for, the builder's estimate included very basic fixtures and fittings, so upgrading those added to the cost.

We are just coming to then end of an extension build. We had a 10% contingency. It's come in at 4% under.

Only cost not factored in was the lawn being ruined. It's cost me £30 in lawn seed, edging and half a day's work (mine).

Yes to including anything which you will lose once they knock down a wall, both on the inside and outside of that wall.

From experience, your builders quote will probably include just the basics of each item, white plastic sockets, basic spotlights etc. If you're anything like me, when you're doing so much building work, you will want it to be finished off really well and also be functional, suddenly you're changing to brushed chrome sockets, some with USB ports, sensor lights in some cupboards etc, oak doors. This stuff really adds up. It really pays to sit down at the start and literally plan every socket, light etc, although that's very hard to do.

We’re having some internal walks knocked down and rebuilt (so no new footprint but still 4 new rooms. The builder is our friend so we have asked him to include decent amounts for the things he’s included in the quote (eg not the cheapest of everything)
however, we will still need to add: light fittings, curtains/rails/track, decorating, carpet and underlay (will prob do on credit) bathroom accessories/ towel rail/loo roll holder etc.
we will need a new sofa (0% deal) and TV
Plus I imagine we’ll spend on things like rugs, mirrors, soft furnishings, new towels. We will do some of the work ourselves but will still need tools, paint, sandpaper etc. our quote is £42k and I imagine we’ll spend £50k.

We are just finishing a single storey extension with new kitchen-diner, and turning the old kitchen into a downstairs loo and utility. Our builder’s quote was to build the extension and convert the old kitchen, to a plaster finish, plus VAT, including decorating the new space.

I estimated we would pay about a third as much again as the quote price (including the VAT) and that’s turned out to be not far off - about 40%. That extra amount (around £32k) includes:

• new kitchen cabinets (DIY Kitchens, solid wood);
• new kitchen appliances and plumbing in existing ones;
• fitting kitchen;
• new worktops;
• new flooring for the extension and loo;
• cost of sanitary fittings;
• paint to decorate the rest of the downstairs;
• cost of sourcing and fitting some new internal doors to separate out the sitting room from the snug;
• installing a water softener;
• basic patio (worth doing when they dig the foundations!);
• replacement of some rotten joists;
• more upmarket light switches;
• light fittings;
• removing an old plastic ceiling and making good;
• installation of ceiling clothes airer;
• removing wallpaper from, and re-skimming, a ceiling.
• getting other downstairs floors professionally sanded.
• storage for much of our downstairs furniture, and transportation there and back.

We have not yet got onto window dressings or new furniture…🤦‍♀️. We need rugs, and I’d really like a new sofa and armchair (ours are 15 years old and well past their best). We need to decorate our sitting room, and I’d like to get more carpentry done but can’t afford that for some time.

Believe me. Whatever you have, you will spend it. And then some.

It does depend what your builder has included.

my builder’s quote included plastering and electrics. I hadn’t thought about lighting or radiators. The quote includes spot lights but I want some feature lighting over the kitchen island. I also want to upgrade radiators and sockets etc.

if it helps there is 10% off in H&M at the moment for online purchases

Thanks all, lots of really helpful advice!

B and q not H&M 😂😂😂