9 September 2026

How Long Does a Loft Conversion Take in North London?

Ashley Chavez Articles

How Long Does a Loft Conversion Take in North London? — Firtree Build

Firtree Build — Loft Conversions, North London

How Long Does a Loft Conversion Take
in North London?

4–6 wksRooflight / Velux build

6–10 wksRear dormer build

10–14 wksMansard build

4–5 moTotal, start to finish

On site, a loft conversion in North London typically takes 4 to 14 weeks to build, depending on the type. That’s the construction period alone though, not the whole project. From first drawings to finished room, a standard dormer conversion in Enfield or North London usually runs 4 to 5 months, and where planning permission and a Party Wall Agreement are both needed, the full programme can stretch to 7 to 9 months. An eight-week build quote and an eight-week project are two different things, and it’s worth knowing which one a builder is actually giving you.

Construction Time by Conversion Type

Loft conversion type	Typical construction time
Rooflight / Velux	4 to 6 weeks
Rear dormer	6 to 10 weeks
Hip-to-gable	8 to 12 weeks
Mansard	10 to 14 weeks

A rooflight conversion is the quickest because the existing roof shape stays largely as it is. A rear dormer adds more structural work to gain headroom and floor space, which is why it’s the most common choice across North London terraces. Hip-to-gable and mansard conversions involve progressively more alteration to the roof structure itself, and the build time grows with it. These are 2026 market ranges, not fixed dates for every property: the existing structure, specification and access all still play a part.

The Full Project Timeline, Not Just the Build

The construction period is only one piece of the timeline. For a standard dormer, Firtree’s benchmark allows around 6 to 10 weeks before construction even starts, covering drawings, structural calculations and Building Regulations preparation. Add that to the build itself and you get the 4 to 5 month figure for a typical permitted development scheme. Where the project needs full planning permission and a Party Wall Agreement on top of that, the overall programme extends to around 7 to 9 months. Comparing builders purely on construction weeks misses most of what actually determines when you’ll have a finished room.

What Needs to Happen Before Construction Starts

The existing loft has to be assessed properly first: available roof height, the existing floor structure, and where the new staircase can realistically go. Structural calculations then set the requirements for the new floor and any steelwork, and drawings and technical information get prepared for Building Regulations alongside that. The planning position needs settling too. Many loft conversions fall under permitted development, but conservation areas and Article 4 Directions across parts of Enfield, Haringey and Barnet can mean full planning permission is needed instead, and that’s worth establishing at the start rather than after the design is finished.

Party Wall Requirements Can Affect the Start Date

Where a loft conversion affects a shared wall or structure, common on terraced and semi-detached North London homes, Party Wall notice requirements apply, and this process runs separately from planning permission and Building Regulations. It matters most for the more substantial structural work involved in hip-to-gable and mansard conversions. Identifying the relevant notice requirements early is what prevents them turning into an unexpected delay to the start date.

What Can Make the Build Run Longer Than Expected

Conversion type sets the baseline, but the existing property has a lot to say too. Older North London houses can hide structural surprises that aren’t obvious on a first viewing: roof timbers needing extra work, a floor structure needing more reinforcement, or a staircase position that creates additional structural requirements once it’s properly assessed. Specification matters as well. A straightforward loft bedroom with standard finishes runs to a different programme than a larger conversion with an en-suite, bespoke joinery and higher-spec finishes throughout, and design changes made after structural calculations are signed off tend to add time, not save it.

Can You Stay in the House During the Build?

Usually, yes. Most of the structural work happens in the loft and is reached through external scaffolding, so the rest of the house stays usable for much of the project. The exception is the staircase opening, which typically lasts a few days and is scheduled in advance. For the full picture on living through a conversion room by room, see our dedicated guide.

Keeping the Project on Schedule

The biggest protection for your programme is resolving the major decisions before work starts on site: the loft assessed properly, the planning position confirmed, structural calculations completed, and the staircase position agreed early since it affects both the loft and the room below. Bathroom layout, electrics and principal finishes are worth locking in at the same time. A quotation based on the same drawings and specification you’ve actually approved gives you a programme that means something, instead of a generic allowance that has little to do with your particular project. The shortest quoted build time isn’t automatically the quickest route to a finished loft.

Helpful Tips Before You Commit to a Programme

Ask for the full project timeline, not just the number of weeks quoted for construction.
Confirm whether your loft falls under permitted development or needs full planning permission, since that changes the whole programme.
Check whether Party Wall notices apply to your project and get them served early.
Agree the staircase position, bathroom layout and principal finishes before construction starts, not during it.
Ask what the quoted programme actually includes: design, structural calculations and inspections, or construction time alone.

Firtree confirms your project programme once the design is established, so your schedule reflects your specific conversion instead of a generic timeframe.

FAQs

How long does a dormer loft conversion take?

Around 6 to 10 weeks on site. From first drawings to completion, a standard dormer in North London usually runs 4 to 5 months, more where planning and Party Wall procedures apply.

Is a rooflight or Velux conversion quicker than a dormer?

Yes. A rooflight conversion typically takes 4 to 6 weeks on site, against 6 to 10 weeks for a rear dormer.

How long does a mansard conversion take?

Around 10 to 14 weeks on site, the longest of the four main types because the roof structure is altered so extensively.

How much does planning permission add to the timeline?

Where full planning permission and a Party Wall Agreement are both required, the overall project typically extends from the usual 4 to 5 months to around 7 to 9 months, on top of the construction period itself.

Can I stay in my house during a loft conversion?

Usually, yes. Most of the build happens in the loft via external scaffolding, with the staircase opening, lasting a few days, the main exception.

What’s the quickest type of loft conversion?

A rooflight or Velux conversion, at around 4 to 6 weeks on site, though it only suits lofts that already have enough height and space without altering the roofline.

Plan Your Loft Conversion with Confidence

The number of weeks a builder quotes for construction is only part of the answer. What actually determines when you’ll have a finished room is the combination of conversion type, pre-construction preparation, and whether planning permission or a Party Wall Agreement are needed on top. For most standard North London dormer conversions, 4 to 5 months from first drawings to completion is the realistic figure to plan around, extending to 7 to 9 months where the full approvals process applies.

Firtree confirms your project programme once the design is established, so your schedule reflects your specific conversion instead of a generic timeframe. If you’re considering a loft conversion in Enfield or elsewhere across North London, get in touch to arrange a free feasibility visit and find out what a realistic programme looks like for your house.

8 September 2026

How Long Does a House Extension Take in North London?

Ashley Chavez Articles house extension, house extension North London, house extension timeline, North London builder

How Long Does a House Extension Take in North London? | Firtree Build

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.

Single storey rear8–12 wks

Double storey12–16 wks

Wraparound14–20 wks

Typical construction time by extension type
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.

8–15 weeks

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.

16–26 weeks

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

Design & building control8–15 weeks Build8–12 weeks Finished roomshorter end of 6–9 months

Full planning permission route: longer end

Design & planning application16–26 weeks Build8–12 weeks Finished roomlonger end of 6–9 months

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.

Ashley Chavez

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