Nothing’s actually wrong. The digger’s just late. But try telling that to someone three days into a build who hasn’t heard from anyone since Monday. Most of the stress people feel during an extension has nothing to do with money and everything to do with not knowing what’s meant to be happening on any given day. Once you know the actual order things happen in, a lot of that stress disappears on its own — a quiet week stops meaning “something’s gone wrong” and starts meaning “oh, that’s just first fix, that’s normal.”
So here’s the order, properly, and why it’s worth knowing before you’re the one standing in the garden wondering.
Before Anything Actually Gets Built
The stage that matters most happens weeks before a brick moves, and it’s the one people are most tempted to rush. Someone needs to physically walk your garden — boundaries, drainage, whatever quirks your specific council has about rear extensions on your street. You can’t guess this stuff over the phone. This is also where you find out, properly, whether you need full planning permission or you’re covered under permitted development, and that one answer changes your entire timeline.
Design comes after that. For a single storey extension, it’s rarely dramatic. Nobody’s designing something that ends up on a renovation show. It’s quieter questions than that — does the new room actually connect sensibly to your existing kitchen, is a roof lantern worth the money given which way your garden faces, does the layout work for how your household actually moves around during a Tuesday morning rather than how it looks in a nice render. Structural sums need to happen right here, alongside the design, not once the drawings are finished and everyone’s already excited about them.
The Waiting Bit Nobody Likes
Once the design’s locked, planning applications go in where they’re needed, plus building regs submissions. Honestly, this is the part most homeowners find hardest, purely because there’s nothing to watch. You’re just waiting on the council’s clock, not yours. A decent contractor tells you the truth about how long that’s likely to take rather than a rosy number picked to keep you smiling for now, one that quietly slips week after week until you stop asking.
If your extension sits along a shared boundary, this is also when party wall agreements need sorting, and it’s exactly the kind of thing that gets left too late if you’re managing it yourself. Neighbours reply when they reply. Good building contractors in London know to start that conversation early rather than chasing a signature the week before groundworks are due.
Groundworks
Digging footings. Laying foundations. Sorting drains that need rerouting. Nobody finds this bit interesting — most homeowners glance at the digger once and go back inside. But it’s exactly where the ground itself tends to reveal problems, if there are any. Older London houses in particular have a habit of hiding old drains nobody remembers, or soil that behaves nothing like the survey assumed. Catch that here, while it’s just mud, and it’s cheap. Catch it three weeks later once concrete’s already down, and it isn’t.
Walls and Roof Going Up
With foundations in, the shape of the thing finally starts to show — brickwork or blockwork, steel where you’re opening into the existing house, the roof itself. This is usually the point a project starts to feel real, because you can stand inside the new space for the first time instead of squinting at a floor plan trying to imagine it.
Windows and doors go in near the end of this stretch, including any bifold or sliding sets. That’s the point the build goes weathertight, and it matters more than people expect, because from here the schedule stops being hostage to whatever the weather’s doing that week.
First Fix: The Bit Nobody Sees Again
Pipework, wiring, underfloor heating loops if you’re having them — all of it goes in now, before plaster comes anywhere near a wall. None of this will ever be seen again once the room’s finished, which is exactly why it needs to be right the first time. Get something wrong here and fixing it later means cutting back into a wall that’s already been plastered and painted — not something anyone wants to be dealing with three weeks before they’re hoping to host people in the new room.
Insulation usually goes in around the same time, and it’s more important than people give it credit for. It’s the difference between an extension you actually sit in come January, and one that quietly turns into a place to store the ironing board.
Second Fix
Once the plaster’s dry, everything speeds up. Sockets, light fittings, radiators or heating controls, the kitchen going in if there is one. This is where the room stops looking like a shell and starts looking like somewhere you’d actually want to be. It’s also where homeowners get pulled into more decisions than at any other point, because from here it’s about taste rather than structure — tiles, paint, flooring, whatever bit of garden landscaping ties the new space back into the rest of the outdoors.
Snagging
This is the stage that separates a contractor who cares from one who’s just trying to get to the next job. Someone should genuinely walk through the finished space — check doors close properly, check finishes are even, fix whatever isn’t quite right — before anyone calls it done. It shouldn’t feel rushed, and it definitely shouldn’t feel like an afterthought squeezed in on the way out the door.
Why Any of This Actually Matters to You
None of this is trivia for its own sake. Knowing the order tells you what’s normal and what isn’t — why a quiet week in the middle doesn’t mean disaster, why noise belongs to some weeks and not others. It also gives you something real to hold a contractor to before you’ve handed over a deposit. Someone who can walk you through this confidently, and keeps you updated as each part wraps up, is generally worth trusting with your home. Someone who waves it off with “it’ll all come together” isn’t.
In Conclusion
Knowing how a build should actually unfold, stage by stage, is one of the clearest ways to judge whether a contractor genuinely knows what they’re doing before you’ve handed over a penny. London Design & Build is one of the leading design & build specialists in London. We specialise in planning applications, building regulation drawings, architectural design, and project management. However you are planning to improve your home, we at London Design & Build are here to help — get in touch for a free site visit, and we’ll walk you through exactly what your single storey extension would look like from first sketch to finished room.
