How much does a loft conversion cost in north London? (2026)

A rear dormer loft conversion in north London costs roughly £70,000 to £85,000 including VAT in 2026, based on our own recent quotes for rear dormers with a bedroom and a shower room or en-suite. A simpler loft with roof windows only costs less, and a mansard costs more.

Public London cost guides land in a similar place once you add VAT and a bathroom. Below is where the money goes, what sits on top of the build price, and the things that push a quote up or down.

What our recent north London lofts have cost

Our most recent loft quotes in north London, all from 2026, have come in between about £72,000 and £85,000 including VAT. The ones we have full detail on were rear dormers with a bedroom and a shower room or en-suite, and one was a hip-to-gable with a rear dormer as well.

So you know what that money bought, those quotes included the following.

• Scaffolding for the length of the job, with a temporary roof
• Taking off the back slope of the roof and building the dormer
• The new floor, stud walls, insulation, plasterboard and skim
• Roof windows and the dormer windows
• Electrics, plumbing and the shower room or en-suite
• Decorating
• Allowances for Building Control and the structural engineer

We haven't priced enough rooflight-only lofts or mansards in north London recently to give our own range for those, so for them use the public figures below.

What public London cost guides say

Here's what four published guides say, so you can see how our numbers compare. Watch the VAT, because most of them quote prices before it.

• Homebuilding & Renovating (updated July 2026) gives UK prices before VAT of £30,000 to £45,000 for a rooflight loft and £45,000 to £75,000 for a dormer. A hip-to-gable is £55,000 to £85,000 and a mansard £70,000 to £120,000 or more. It says London and the South East can be 15% to 30% more.
• Simply Loft (updated August 2026), a London loft firm, gives £55,000 to £80,000 for a dormer and says an average London loft is £50,000 to £90,000. Its page isn't clear whether that includes VAT.
• Resi (October 2025), a London architecture firm, gives an average London rear dormer of about £56,000 before VAT, not including glazing, bathrooms or professional fees.
• HomeOwners Alliance (updated July 2026) gives UK averages of about £50,000 for a dormer and £60,000 for a hip-to-gable.

Take a London dormer at £55,000 to £70,000 before VAT, add 20% VAT and a shower room, and you're at roughly our range. That's a fair sanity check.

The fees on top of the build

The build price is the biggest number, but it isn't the only one. Homebuilding & Renovating's 2026 figures for the usual extras are these.

• Architectural drawings, about £1,500 to £4,000
• Structural engineer, about £750 to £2,500
• Building Regulations, about £600 to £1,500
• Party wall surveyor, about £1,000 to £2,500 or more if your neighbour appoints one

If your loft needs planning permission, there's a council fee too, £548 for a house from April 2026. If it's permitted development, a lawful development certificate is £274, and it's worth having. Our guide to loft conversions and permitted development in Barnet and Haringey explains which you're likely to need. If you share a wall with a neighbour, read our guide to party wall notices as well.

What pushes a loft price up or down

The type of loft. A rooflight conversion keeps the roof as it is and adds windows, so it's the cheapest, but you only get headroom down the middle. A rear dormer adds a box out of the back slope and gives you straight walls. A hip-to-gable rebuilds the sloping side of a semi or end of terrace as a flat gable wall, which adds cost. A mansard rebuilds the whole back slope and nearly always needs planning. Our guide on rear dormer or hip-to-gable explains the choice.

Headroom. You need enough height over the stairs and in the room. If the loft is low, the fix is either lowering the ceilings below or raising the roof, and both cost money.

Steel beams. Most dormers need steel beams to carry the roof once the back slope comes off. The structural engineer decides how many and what size, and the crane or lifting gear to get them in is part of the cost.

The bathroom. A shower room is cheaper than a bathroom with a freestanding bath. And the fittings you choose can swing the price by thousands.

Getting materials in. On a north London terrace with no side access, everything goes up the scaffold from the street. A skip on the road needs a council permit. None of this is unusual, but it's one of the reasons London lofts cost more than the same loft in the Midlands.

Glazing. Wide glazing at the back of the dormer makes the room, but big black-framed sliders cost far more than a standard window.

How to keep the cost down

• Go full width on a terrace. The extra width costs little compared with the rest of the dormer, so the price per square metre drops.
• Keep the bathroom above the one below. Short waste and water runs are cheaper and easier.
• Use the low space. Eaves storage and a bath under the slope make the most of room you're paying for anyway.
• Fix the spec before you get quotes. Pick the windows and the bathroom level, so every builder is pricing the same loft.

Our guide 7 ways to get more loft for your money goes into this in more detail.

Paying for it

We don't take a deposit. You pay weekly in arrears, with an invoice every Friday for the work done that week. You're never paying for work that hasn't happened yet, and you can see the job moving before each payment.

See one we built

Our loft conversion in Bounds Green is a full-width rear dormer on a terrace, with a bedroom and a bathroom. We wrote up how it went in our Bounds Green case study, with photos from every stage.

Sources and dates

• Promaester, our own 2026 loft quotes in north London, shown as a rounded range only. Prices include VAT at 20%.
• Homebuilding & Renovating, Loft conversion costs, updated 29 July 2026, checked 5 October 2026.
• Simply Loft, How much does a loft conversion cost in London, updated 27 August 2026, checked 5 October 2026.
• Resi, Loft conversion costs 2025, published 2 October 2025, checked 5 October 2026.
• HomeOwners Alliance, Loft conversion costs, updated 28 July 2026, checked 5 October 2026.
• gov.uk, Planning fees from 1 April 2026, checked 5 October 2026.

Every loft is different, so these are guide figures, not a quote. If you want a real number for yours, book a free site visit. We'll look at the roof, the stairs and the access, and give you a fixed, itemised quote.