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Extension post #11 – how much did it cost?

How much we spent on our single storey rear extension, down to the last light bulb.

Whilst talking about money doesn’t come naturally to us British folk, it seems daft to write loads of posts about our extension without covering the reality of how much it all cost. Before we decided to have work done, I found very little helpful content online about the cost of extensions other than “between £1,000 and £3,000 per square metre” which is useless. So if y’all are thinking of having similar work done, or are simply nosey (as I would be), read on for a breakdown of how much our extension cost.


Pre-building work

There were a few costs before the builders arrived. These included architect fees (£775), planning application (£84) and structural engineer calculations (£714) which meant we’d spent £1,573 before anything actually changed. We could have saved money by not using an architect and just going with the builder’s interpretation of what we wanted, but we felt this was too risky.

Building work

If you’ve been following my extension posts, you’ll have a good idea of what the work included. As well as a 3 x 6 metre single pitch roof extension, we had a loo put in under the stairs and our side door moved to allow access straight into the new utility. You can see more details in the post I wrote about our plans.

Our builder project managed the work and we agreed a fixed price contract before the build began. This contract included doing all the work except for supplying/fitting the kitchen, laying the flooring and decorating. So electrics, plumbing and plastering, steels etc. were all included in the price.

The total cost of the planned building work was £37,700. I’ve written a bit more about the quotes we had in this post about choosing our architect and builder.

Any deviations from the contract meant we’d either have to pay more/less than the figure we’d agreed. As you might expect, we added more bits than we removed. This included adding another Velux, lighting above/below kitchen units, upgrading to column radiators and quite a few extra electric and plumbing bits. The extra Velux cost £365, extra electrics £775, and extra plumbing £540. We knew that we’d inevitably want to add a few bits here and there so thankfully had 10% extra planned into the budget.

So, all-in-all, all the building work plus extra bits came to £39,380. We were very lucky to have no unexpected costs during the build – I reckon that’s very rare!

Kitchen & utility

This was our next biggest cost. The kitchen & utility units came to £4,247 which for 20 units plus all the trim is crazy good. That’s because we ordered from DIY Kitchens who are significantly cheaper than elsewhere. I sounds like I’m being paid to write this but I am not (although if anyone from DIY Kitchens is reading this, gizza bell). This post is about how we planned and ordered our units.

We ordered our laminate worktops and upstands separately – these came to £617. I didn’t trust myself to fit the worktops so we paid a chap £145 to do these.

On top of that, knobs and cups for the units cost £138 which seems a ridiculous amount to spend on this but trust me, it adds up.

The sink cost £160 and tap came in at an offensively cheap £28 (let’s see how long it lasts…)

We’ve bought the tiles for our kitchen splashback but I ain’t put them up yet. These cost £125.

Then there were various other, smaller costs including pendants & bulbs for the island as well as all the other fixings I bought to use whilst fitting the kitchen/utility which came to £230 in total.

SO, absolutely all of these bits came to £5,690 which I think is quite good for a decent-sized kitchen and utility. Fitting the units ourselves probably saved us between £2,000 and £3,000, although we did have a quote of almost £4K.

Appliances

When it came to choosing our appliances, it was a bit overwhelming to begin with. We soon decided to just buy whatever Which? recommended, providing it was sensibly priced. Appliances came to £2,504 in total, broken down as follows:

  • Stoves range & extractor hood – £988
  • Hisense integrated fridge freezer – £307
  • Bosch washing machine – £400
  • Bosch tumble dryer – £500
  • Integrated Hisense dishwasher – £309

Flooring

We’ve had Karndean LVT flooring fitted to the extension, dining area and utility. This came to around 35sq. metres and cost £2,045, including fitting. This felt like a lot to pay for flooring but it should last a lot longer than any other alternative and so will hopefully be worth it in the long run.

W/C

The building contract didn’t include the loo vanity unit & tap or supply/fitting of tiles. These costs came to £368.

Decorating

Haz saved us a load of cash by doing all the decorating (she has now painted every square inch of the house). So we only had to pay for paint, paintbrushes etc. which came to £164. I think it would have been £1,000+ if we’d used a decorator.

Sundry

Who doesn’t love a sundry category? The place where you put stuff that you didn’t budget for. This included pendant cables for the island lights, door knobs & dipping the doors we bought from FB marketplace. Cost = £92.

The numbers are in…

In case you’re not phenomenally good at mental arithmetic, the total cost of the extension + other bits came to £51,274 (give or take a couple of quid). The original budget we set was £55K, including a small contingency, so we’re glad to have come in under that figure.

Whilst it feels good to imagine that we’ve added more value than that to the house, it shouldn’t matter too much as we plan on living here for a looong time.

It’s worth mentioning that these figures don’t include furniture, the patio that I laid outside the extension, or any of various bits we’ve bought to make the new space look pretty. As you might expect, these add up, so I’d definitely recommend budgeting for this stuff.


It feels a little odd being so transparent about what we spent on the extension but I hope that it’ll prove really useful to some of you guys when budgeting for your own work. We’re based in Yorkshire so probably worth lobbing an extra chunk of cash to your budget if you’re in London/South East.

I’ve said it before but DEFINITELY get multiple quotes for the work. We got 5 quotes and they varied by £17K… So unless you’ve got a spare 17 grand knocking around, it’s worth getting in touch with a few builders.

2 replies on “Extension post #11 – how much did it cost?”

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