Until it’s too late and the scaffolding’s up.
Here’s the thing. Most builders won’t lie to you. But that doesn’t mean they’ll tell you everything. Not upfront. Not until the paperwork’s signed and the skip’s in your front garden.
That’s not to say they’re dodgy. They just know how this works: By the time the steel goes in, it’s a bit late to change your mind.
If you’re planning a loft extension in London—or anywhere, really—there are a few things worth knowing. The sort of stuff that can save you money, hassle, or the sharp shock of your living room being open to the weather for longer than you’d planned.
Let’s get into it.
1. The design might look good on paper—but not in real life
Architects can draw anything.
But not everything drawn gets built the way you imagined.
That sleek open-plan kitchen? Turns out the steels needed to hold it up mean your ceiling’s now lower.
That extra bedroom? The head height under the sloped roof makes it feel more like a cupboard.
Builders will build to spec. But they don’t always stop to ask if that spec actually works for the way you live.
Get someone who understands both structure and layout. Otherwise, you could end up with a beautiful room… that no one wants to use.
2. You might not get planning permission—and they knew it
Some builders say things like:
“You’ll be fine—it’s just a rear extension.”
But then the council steps in. Because you’re in a conservation area. Or your extension blocks the light to your neighbour’s kitchen. Or your build doesn’t follow the Local Plan.
Now you’re stuck.
You’ve paid for drawings. Maybe even a deposit. And you’re being told to go back to square one.
Before you start, make sure someone’s actually checked your property—not just your postcode.
3. Budget creep is a real thing
You’re quoted £80K. You plan for £85K. You’re billed for £95K.
It starts small.
“We found an issue with the drainage.”
“The party wall survey took longer.”
“The roof tiles you picked are discontinued.”
Each one sounds reasonable. But put together, they punch a hole in your budget.
Always ask your builder what’s not included.
Skip hire? Kitchen fitting? Painting? And get it in writing.
4. You’ll still be living there—and it’s not fun
Most people don’t move out during a home extension. And builders know that.
But they won’t always say how rough it gets.
- Dust everywhere.
- Doors off hinges.
- Temporary kitchens in the hallway.
- Waking up to shouting and drilling at 7:59am.
You need to plan for it. Zone off part of the house if you can. Or set up somewhere else for a few weeks if the budget allows.
5. Neighbours will complain if you surprise them
Legally, you don’t need your neighbour’s permission for most extensions.But practically, upsetting them can be expensive.
Objections delay planning.They can call Building Control on you. Or worse—lawyers.
Give them a heads-up. Show them the drawings. Ask if they have concerns. Even if you don’t change anything, it keeps things civil—and smoother.
6. Builders are not always designers
Some builders like A2 Building are great at what they do. But don’t expect them to make layout decisions for you.
If you ask:
“Where should the sockets go?”
Or
“Do you think this window’s big enough?”
You might get a shrug. Or a guess.
They’ll build what you tell them to. But if you don’t tell them, they’ll just crack on.
Make decisions early. And get them on the plan.
7. It will always take longer than you hoped
Even if your builder’s good. Even if the weather holds. Even if everything arrives on time.
Someone somewhere will be late, sick, stuck in traffic or send the wrong batch of tiles.
Plan for slippage. If they say 10 weeks, prepare for 12. And don’t schedule a birthday party for the first weekend after handover.
FAQs
Do I always need planning permission for a home extension?
Not always. Some rear and side extensions fall under permitted development. But that depends on size, height, and location. It’s best to check with the council—or get a lawful development certificate.
What’s the best time of year to start an extension?
Builders work year-round. But dry months (April to September) usually mean fewer weather delays. Just book early—summer slots go fast.
Will I need to move out during the build?
Not necessarily. But it will get messy. If you’ve got young kids or work from home, think carefully about how you’ll manage.
What’s a party wall notice, and do I need one?
If your build is near or on a shared wall or boundary, you’ll need to serve notice to your neighbour. In some cases, you may need a surveyor too.
Can a builder give me advice on design?
Some can. But many just follow drawings. If you want help with layouts, lighting, and flow, get an architect or interior designer involved.
Final word
Home extensions can transform how you live. But they’re not simple—and they’re not something to wing.
Builders don’t always tell you the full picture upfront. Not because they’re dodgy. Just because they’ve seen it all before and forget you haven’t.
Ask the awkward questions. Get things on paper. And treat your extension like what it is—a big investment in your home, your life, and your sanity.
Thinking about extending? Start with the right team.
