Nearly everyone who rings us about an extension starts with the same sentence. “We just need more space.”
And we understand why. The kitchen’s too small, the kids have got bigger, someone’s been working from the ironing board since 2020, and moving in London costs a fortune. So the obvious plan is to push the back of the house out as far as it’ll go.
Here’s what we’ve learned after a lot of these, though. More space and a better house aren’t the same thing. We’ve walked into extensions other people built, big, expensive ones, where the owners were quietly disappointed and couldn’t quite say why. The room was huge. It was also dark in the middle, cold by the doors and so noisy you couldn’t hear the telly over the dishwasher.
London makes it harder, too. Narrow terraces, no side access, neighbours a metre away, planning issues, old brickwork that doesn’t like being messed with. You can’t bully your way past any of that just by building bigger. So in 2026, with build costs where they are, the question we keep asking clients is a simple one. What’s actually annoying you about the house at the moment?
These are the six things we end up talking about most.
1. Bigger is not always better
This one surprises people. A deep rear extension looks brilliant on the drawings. All those square metres. But build one straight across the back of a terrace without thinking about light, and the old middle room, which used to have a window, now has none. It becomes a sort of dim corridor you walk through to get to the nice bit. The house got bigger, and one of its rooms got worse.
We’d rather start by walking round the house with you and finding out what bugs you about it. Sometimes it really is floor area. Quite often, though, it’s light, or the way the kitchen connects to the garden, or a more useful kitchen layout, or just somewhere to put the coats and the shoes and the recycling. None of that needs the biggest possible box.
A slightly smaller extension with a long rooflight over the join between old and new, a higher ceiling and doors in the right place will often beat one that’s two metres deeper. We’ve seen a 30 square metre room feel more generous than a 40 square metre one, simply because the light got all the way in.
So yes, bigger can be better. But only if the design’s earning it.
2. Warmth, insulation and build quality matter more than people think
People spend weeks choosing taps. Months, sometimes, on the kitchen. Then when we get to insulation, the conversation is often one line long: “as long as it passes Building Control”.
Thing is, passing the minimum standard is just that. The minimum. Building Control check you’ve met the rules, and the rules were written to stop bad buildings, so they don’t promise you a cosy one.
And it’s where a lot of extensions let people down without anyone noticing at first. Handover day, everything looks great. Then November comes. The floor’s cold. There’s a chilly strip by the big glass doors. A bit of black mould shows up in the corner where the new roof meets the old wall. Nobody did anything dramatically wrong. It’s usually a pile of small things: a gap in the insulation here, a cold bridge there, more glass than the heating can cope with, a junction nobody bothered detailing properly.
What you want is a room that’s as nice to sit in on a wet Tuesday in January as it looks in the June photos. That comes from the boring bits, the floor build-up, the roof, the walls, the spec of the glazing and how all of it joins together. None of it ends up on Instagram, sadly. You’ll notice it every winter though.
3. Open-plan is not always the answer
For about fifteen years the dream was one huge kitchen-living-dining room. Knock everything through, one big bright space, done.
Then people started living in them. The dishwasher’s going, someone’s on a Teams call, the extractor’s on, the kids are doing homework at the island and somebody else is trying to watch something with the sound up. There’s nowhere to go. Looks lovely in the architect’s render. By Thursday evening it’s hard work.
We’re not saying go back to lots of small dark rooms. Nobody wants that. But a family house in London has to do several jobs at once now, and a single room can’t do all of them quietly.
What tends to work is a bit of separation that doesn’t kill the light. A snug off the main space. A glazed internal screen (the Crittall-style ones are popular for good reason). A step down into the living area. A run of built-in joinery that quietly splits the cooking end from the sitting end. Small moves, really, but they’re often the difference between a house that photographs well and one that’s nice to come home to.
4. In London, access can change the whole job
Nobody gets excited about access. It’s still one of the things that most changes what an extension costs and how stressful it is.
Lots of terraces have no side access at all, so every bag of cement, every bit of steel and every tonne of soil goes in and out through the front door and down the hall. Parking’s a fight. A crane might be out of the question. The skip needs a council licence, and sometimes a parking bay suspension on top, which you pay for by the day.
This is where quotes can mislead you. One price is lower, and it looks like better value. But if that quote has quietly ignored the fact that the soil from the foundations will have to be bagged up and wheelbarrowed through your house, it won’t stay lower for long. The steels might have to be made in sections and bolted together on site because a 6 metre beam won’t go round the corner at the bottom of the stairs. All of that is time, and time is labour.
We’d much rather have that conversation before anything starts. How will the materials get in, where does the muck go, which permits does the council want, will the neighbours be affected? Boring, yes. Saves a lot of grief though.
5. The right materials are not always the traditional ones
Brick has a funny hold on people. We’ve had clients say, quite seriously, that a timber-framed extension “wouldn’t feel like a real house”. And to be fair, if the new bit has to match a Victorian back wall or it’s on show from the street, brick is often what we’d suggest anyway.
But we’ve also built timber-frame extensions that were watertight about three weeks sooner than the brick version would have been, because there’s no waiting around for mortar and blockwork to dry. You can get more insulation into a thinner wall, which on a narrow plot gives you a few extra centimetres of room on each side. People laugh when we say that matters. Then they see the kitchen plans.
Glazing is the other thing. Slim aluminium frames let in a surprising amount more light than chunky old-style ones, and on a terrace, where the back of the house might only get sun for a couple of hours, that’s a big deal. One of our lads says light is the most important material on the job. Sounds a bit much, but he’s not wrong.
We’re not anti-brick, honestly. We just don’t think it should be picked because “that’s what you do”.
6. Build for the years ahead, not just for handover day
Everyone pictures the first evening. Doors open, new island, a glass of something, the lights just right. We do too, it’s the best part of the job.
Then real life carries on. The playroom turns into a homework room, then a place for a grumpy fifteen-year-old to hide, then maybe your office. Energy bills go up again. The trendy tiles you loved start to look very 2026.
The extensions that still feel right years later tend to have a warm, well-sealed shell, sensible layout choices, materials that can take a few winters and plenty of storage. Thoughtful lighting helps too, something better than a ceiling full of downlights in neat rows. And it’s worth having a builder who’ll come back for maintenance when the odd thing needs a look.
Most owners can’t explain why one extension still feels good after five years and another one gets on their nerves. When we look at them, it’s nearly always this stuff.
Final thoughts
If you take one thing from all this, walk round your house before you look at a single drawing and make a note of what actually annoys you. The dark hallway. The kitchen you can’t get two people into. The fact you can hear the TV in every room. Then build to fix those.
It might end up a big extension, it might be a small one. Either’s fine, so long as the house is nicer to live in afterwards. That’s really all we’re trying to do.
FAQ
1) What is the “square footage trap” in a London extension?
Basically, going for the biggest number on the drawing and forgetting about light. You end up with a dark middle room that nobody uses, which is a pricey way to gain floor space.
2) Is a smaller extension ever better than a bigger one?
Often, yes. We’ve seen 30 square metres, done well, feel roomier than a dull 40.
3) What does “flow” mean in extension design?
How you actually get around the house. From the front door to the kettle, from the kitchen to the garden, where the bags get dumped. If the extension makes any of that awkward, the flow’s wrong.
4) What is a “thermal envelope” and why does it matter?
Think of it as the duvet round your house: insulation plus an airtight layer, with no holes in it. Leave gaps at the joins and you’re heating the street.
5) Isn’t “meeting Building Regulations” enough?
It gets you signed off. Whether you’re warm in February is another question, and the regs set a floor rather than a target.
6) What is thermal bridging and why is it a big deal?
Heat sneaking past the insulation through something solid, a steel beam or a concrete lintel, for instance. You get a cold patch on the wall, then condensation, then mould. Roof-to-wall junctions are the usual suspects.
7) Can a house be airtight and still “breathe”?
Yes. Airtight means no random draughts. Ventilation is the fresh air you let in on purpose, through trickle vents, decent extractor fans or a whole-house system.
8) Are big glass walls a problem for warmth?
They can be. Glass loses more heat than a wall does, even the good stuff, and if it faces south it’ll bake you in summer. Ask about U-values and shading before you fall in love with the view.
9) What’s the downside of open-plan living in 2026?
Noise, mainly. And the smell of last night’s curry, which follows you to the sofa.
10) What is “broken-plan” and how is it different from open-plan?
Still one big bright space, but with a few ways to split it up, like a half wall, a step down, a bit of joinery or a glazed screen. Each end can then get on with its own thing.
11) Will broken-plan make my home feel smaller or darker?
Not if it’s done properly. You keep the light and the long views through. It’s mostly the noise that gets cut.
12) What are Crittall-style partitions and why use them?
Those slim black steel-and-glass screens you’ll have seen everywhere. They let light through but you can still shut the door on the extractor fan.
13) Why do “tight access” sites cost more in London?
Because half the work turns into carrying things. If there’s no side access, everything comes through your hallway, by hand, and that’s slower and needs more people.
14) What’s the “skip nightmare” and why should I care?
In places like Richmond or Putney a skip on the road needs a council licence, sometimes a parking bay suspension as well, and neighbours who don’t mind. It’s a cost every day the job runs.
15) What is “muck away” and why does it blow budgets?
It’s getting the soil out once the foundations are dug. With no way to get a digger round the back, it’s bags, barrows and a lot of trips. A surprising amount of money goes on it.
16) Why do steel installs get complicated on terraced houses?
A 6 metre beam and a narrow Victorian hallway don’t get on. So it’s either a crane, or the steel gets made in sections and bolted together where it’s going.
17) Why are timber frames and specialist glazing becoming more popular than brick?
Speed mostly. Timber frame goes up quickly and there’s no waiting for things to dry. You can also get more insulation into a slimmer wall.
18) Does timber feel less “solid” than brick?
Honestly, once it’s plastered you’d struggle to tell. Modern frames are stiff and strong, and they can span further than you’d think.
19) Is brick still worth using sometimes?
Of course. If it needs to match the house or the street, brick’s often the right call. Just pick it on purpose.
20) What does “future-proofing” an extension actually mean?
Thinking about what the room might be in ten years. An office, a granny annexe, a teenager’s den. Plus a warm enough build that a heat pump will cope if you switch later.
21) Why should I prioritise “hidden value” over finishes?
Because swapping a worktop takes a weekend. Fixing bad insulation means taking the room apart.
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Force Builders Ltd is a London building company (Companies House 07049787) delivering house extensions, loft conversions and full refurbishments across Greater London. See our projects or get in touch.