The first question I get asked about a loft conversion is not “can you do it?” – it’s “what will it cost?” Fair enough. It’s a big spend, and most people want a realistic number before they call anyone. So here it is, as straight as I can put it, based on the lofts we build around Mill Hill, Barnet, Finchley and the rest of North-West London.
Loft conversion prices in North London – 2026
These are typical all-in ranges for a good-quality job in our area, including the structural work, staircase, insulation, plastering, electrics, plumbing and a standard finish. Every house is different, so treat these as a starting point rather than a quote.
| Type of loft conversion | Typical cost (North London, 2026) | Best suited to |
|---|---|---|
| Rooflight (Velux) conversion | £40,000 – £60,000 | Lofts with good head height already; keeps the roofline unchanged |
| Rear dormer | £55,000 – £85,000 | Most 1930s semis and Victorian terraces – the most common type in our area |
| Hip-to-gable (often with a rear dormer) | £65,000 – £95,000 | Semi-detached and end-of-terrace houses with a hipped roof |
| Mansard | £75,000 – £120,000+ | Terraces where you want the maximum space and a proper extra floor |
Add a bathroom or en-suite and you’re usually looking at another £8,000 to £15,000 depending on the spec. Bespoke joinery, a glass balustrade or high-end flooring all push the number up again – and that’s fine, as long as you know that going in.
What pushes the price up
The roof you’ve got. A hipped roof (sloping on three sides) usually needs a hip-to-gable to make the space worthwhile, which is more steelwork and brickwork than a simple dormer.
Head height. If you’ve got less than about 2.2 metres from the top of the ceiling joists to the ridge, we may need to lower ceilings below or raise the roof. That’s a much bigger job.
The staircase. This is the bit people underestimate. Getting a compliant staircase in without stealing a bedroom sometimes means moving walls on the floor below. On a lot of 1930s houses in Mill Hill it goes above the existing stairs neatly; on some Victorian terraces it takes a bit more thought.
Structure. Steel beams, a structural engineer’s calculations and Building Control sign-off are non-negotiable. Where the steels have to go, and how big they are, makes a real difference.
Plumbing and heating. An en-suite is straightforward if the soil stack is in the right place; less so if it isn’t. Your boiler may also need looking at if you’re adding radiators or a shower.
Finish. Standard skirting and a decent carpet is one price. Oak flooring, fitted wardrobes and a walk-in shower is another. Neither is wrong – it’s your home.
What keeps the price down
A loft with good existing height, a simple rear dormer, keeping the bathroom close to the existing plumbing, and – honestly – making decisions early. Changes mid-build are where budgets drift, on any job, with any builder.
What’s usually included, and what isn’t
When we quote a loft, the quote covers scaffolding, structural steels, floor joists, the dormer or roof alterations, insulation to current Building Regulations, windows, staircase, plasterboard and skim, first and second fix electrics and plumbing, fire doors and smoke alarms where required, and making good. What is normally separate: architect’s drawings, structural engineer’s fees, planning or Building Control fees, a party wall surveyor if your neighbour needs one, and decoration and furniture. I’d rather list all of that upfront than have it turn up as a surprise.
Is it worth it?
In Mill Hill, Barnet and Hampstead Garden Suburb, a well-built loft with a bedroom and en-suite generally adds more to the value of the house than it costs – and, more to the point, it gives a growing family the space to stay in a street they like rather than move. I’ll write more about the “improve or move” question separately, but in short: for most three-bed semis around here, a loft is the best value square footage you can add.
How to get a proper number for your house
The only accurate price is one based on your actual loft. If you’re in Mill Hill, Barnet, Finchley, Hampstead, Edgware or anywhere in North-West London, get in touch and we’ll come and have a look, talk through what you want, and give you a clear written quote with nothing hidden. We work with good local architects, structural engineers and party wall surveyors and can introduce you if you don’t have them yet. And when the job’s done, we come back and sort any snags – that’s part of how we work.
Want to discuss your project? Call us or send a message through the contact page and we’ll arrange a free consultation (we take calls Monday to Friday, 10am to 2pm).