Firtree Build: House Extensions, North London
How Long Does a House Extension Take in North London?
Quick answer
6–9 months
First drawing to finished room, standard single storey extension
A single storey rear extension typically takes 8 to 12 weeks to build once work starts on site. A double storey extension usually runs 12 to 16 weeks, and a wraparound extension 14 to 20 weeks. Those figures cover construction only. Add in design, structural drawings and building control, or a full planning application where one is needed, and a standard single storey extension in Enfield or North London usually takes around 6 to 9 months from the first drawing to the finished room.
That gap between the build time and the total project time catches a lot of homeowners out. If you have had a builder quote a 10 week build and started counting down from the day you first picked up the phone, it is worth understanding why the two figures are not the same thing, and what actually fills the time in between.
What the build time on site actually covers
When a builder gives you a construction timeframe, they mean the period from the first day on site to practical completion: groundworks, structural work, roofing, first fix, plastering, second fix and decoration. It does not include anything that happens before the digger arrives, and on most projects that preparation stage takes longer than any single week of the build itself.
| Extension type | Typical construction time |
|---|---|
| Single storey rear extension | 8 to 12 weeks |
| Double storey extension | 12 to 16 weeks |
| Wraparound extension | 14 to 20 weeks |
These are typical ranges for a straightforward project. Larger footprints, more complex structural work, or difficult site access can push any of these figures towards the upper end, and a compact, simple layout can sometimes land at the lower end.
What happens before construction starts
Before a single brick is laid, most projects go through the same broad sequence: initial design and layout, structural drawings and calculations, and either a building control submission or a planning application, depending on the route your project takes.
If your extension qualifies as permitted development
Many single storey rear extensions in North London do not need planning permission because they fall within permitted development limits. Where that applies, you should still allow around 8 to 15 weeks for design, structural drawings and building control before work can start. This covers the time needed to finalise the layout, produce structural calculations for beams or foundations, and get the building control submission approved or a building notice accepted.
If your extension needs full planning permission
If you are in a conservation area, an Article 4 direction applies, the property is listed, or your design goes beyond permitted development limits, you will need a full householder planning application. Allow around 16 to 26 weeks for this route. That figure includes preparing a fuller set of drawings, the council’s statutory determination period, and the building control process that still has to happen afterwards, since planning permission and building regulations approval are two separate things.
Conservation areas and Article 4 directions are common in parts of Enfield, Haringey and Barnet, so it is worth checking your specific address early rather than assuming permitted development applies.
Adding it up: a realistic total timeline
Put the two halves together and a standard single storey extension in Enfield or North London usually runs to around 6 to 9 months from the first drawing to the finished room. A permitted development project with a straightforward 8 to 12 week build and 8 to 15 weeks of preparation sits towards the shorter end. A project that needs full planning permission, with 16 to 26 weeks of preparation on top of the same build period, sits towards the longer end.
Permitted development route: shorter end
Full planning permission route: longer end
This is a guide to the shape of a typical project, not a fixed promise for every property. Larger double storey and wraparound extensions add time on site, and any project can be affected by the specific circumstances of the plot, such as party wall discussions, structural surveys, or the availability of long lead items like bifold doors or roof lanterns.
How the type of extension changes the total picture
The construction period is only one half of the equation, and it is not the half that varies most between projects. A single storey rear extension and a wraparound extension might only differ by a few weeks on site, but the pre construction stage, particularly whether a full planning application is needed, can add several months to one project and not the other. When comparing timelines across different extension types, it is worth looking at both halves together rather than focusing on the build weeks alone.
Party wall timing
Not every extension built up to or near a boundary triggers the Party Wall etc. Act 1996, and where it does, the notice period depends on the type of work rather than a single standard figure. Work directly to an existing shared wall, such as cutting in, underpinning, or raising it, needs a party structure notice with at least two months’ notice before work starts. Excavating foundations within 3 to 6 metres of a neighbour’s building, depending on depth, needs a separate notice of adjacent excavation, which requires at least one month’s notice. Building a new wall on the boundary line itself also needs one month’s notice. Because these notice periods can run alongside, rather than after, the design and planning stage, it is worth checking early which of them, if any, apply to your specific project rather than assuming a single blanket timeframe.
Why a 10 week build does not mean a 10 week wait
It is easy to hear a builder’s construction estimate and assume the whole process will be over in that time. In practice, the weeks before the build starts, drawing up the design, getting structural calculations right, and clearing building control or planning, are just as much a part of the project as the weeks with a digger on your driveway. Treating the two as separate stages, each with its own realistic timeframe, makes it much easier to plan around the project rather than being caught out by it.
Planning your own timeline
If you are trying to work out roughly when your extension might be finished, start by establishing which route applies to your property: permitted development or full planning permission. That single decision has more effect on your total timeline than almost anything else, since it changes the pre construction period by several months.
- Get a feasibility check early so you know whether permitted development applies before you commission full drawings.
- Ask any builder for a stage by stage build programme, not just a single overall figure, so you can see where the weeks are actually going.
- Check early which, if any, Party Wall Act notices apply to your project, since the different notice periods can affect how far ahead you need to plan.
- On many projects, items with longer lead times, such as bespoke glazing or roof lanterns, are worth ordering as early as the programme allows.
- Build a sensible contingency into your own expectations, particularly for older North London properties where groundwork can throw up surprises.
Our approach
Firtree Build provides a fixed build programme once your drawings are signed off, so once the design stage is complete, you know the construction weeks with reasonable confidence. The variable most families underestimate is the design, drawings and approval stage before that point, which is why it is worth planning for it from day one rather than treating it as an afterthought.
Frequently Asked Questions
How long does a single storey extension take to build?
Once work starts on site, a single storey rear extension typically takes 8 to 12 weeks. This does not include the design, drawings and building control or planning time beforehand.
How long does a double storey extension take?
A double storey extension typically takes 12 to 16 weeks to build on site, reflecting the additional structural work and finishing across two floors.
How long does a wraparound extension take?
A wraparound extension, combining a rear and side return, typically takes 14 to 20 weeks to build once work starts, due to the larger footprint and more complex structural work involved.
Do I need planning permission for my extension, and how does that affect the timeline?
Many single storey rear extensions fall under permitted development and do not need planning permission, which typically means 8 to 15 weeks of design and building control time before work starts. If full planning permission is required, for example in a conservation area, allow 16 to 26 weeks instead.
How long does a house extension take from start to finish in North London?
A standard single storey extension in Enfield or North London usually takes around 6 to 9 months from the first drawing to the finished room, once design, drawings, approvals and construction are all added together.
Getting a realistic timeline for your project
General ranges are a useful starting point, but the only way to know how long your specific extension will take is a proper site visit and a stage by stage programme drawn up around your property, your design and the planning route that applies to you.
If you are at the stage of weighing up costs, value and timeframes together, our guides to extension costs and the value an extension can add cover the other two questions most North London homeowners ask before committing to a project.
Next steps
If you are considering an extension in North London, the next step is to establish which planning route applies to your property and get a proper feasibility check before committing to full drawings. Firtree offers a free feasibility visit and provides a fixed build programme once your drawings are signed off, so you know from the outset roughly when work will start and how long it will run.