If you're a homeowner in Barnet or North London thinking about converting your loft, the first question you'll almost certainly ask is: how much is it going to cost?
The honest answer is that loft conversion costs vary significantly depending on the type of conversion, the size of your property, and the specification of finishes you choose. But as builders who have completed dozens of loft conversions across Barnet, Mill Hill, Finchley, Hampstead and the surrounding areas, we can give you a realistic and detailed breakdown.
Average Loft Conversion Costs in Barnet (2026)
Here's a general guide to what you can expect to pay for a loft conversion in the Barnet and North London area:
Dormer Loft Conversion: £45,000 – £65,000. The most popular type in North London. A dormer extends vertically from the existing roof slope, creating a box-shaped structure that dramatically increases headroom and usable floor space. Ideal for 1930s semis and terraced houses common across Barnet, Mill Hill and Whetstone.
Hip-to-Gable Loft Conversion: £50,000 – £70,000. Common on detached and semi-detached homes with hipped roofs. The sloping hip end of the roof is replaced with a vertical gable wall, creating significantly more internal space. Often combined with a rear dormer for maximum impact.
L-Shaped Loft Conversion: £60,000 – £80,000. Combines a rear dormer with an additional extension over the back addition of the property. Exceptionally popular in North London terraced properties and one of the best ways to maximise space.
Mansard Loft Conversion: £65,000 – £90,000. The most substantial type of loft conversion. Common in conservation areas like Hampstead and Highgate. Always requires planning permission — which we manage on your behalf.
Velux / Roof Light Conversion: £25,000 – £40,000. The most affordable option. Only suitable where there is already adequate headroom in the existing loft space.
What Affects the Cost of a Loft Conversion?
Several factors will influence the final cost of your project: property type and roof structure; size of the conversion; type of conversion chosen; specification and finishes (standard versus premium can add £10,000–£25,000); structural engineer and planning fees (typically £2,000–£5,000); and party wall agreements if applicable (£700–£1,500 per neighbour).
Does a Loft Conversion Add Value?
Yes — consistently and significantly. A well-executed loft conversion typically adds 15–25% to the value of a property in North London. Given current property values in Barnet, Hampstead and Mill Hill, this can represent an increase of £100,000–£250,000 or more on your home's market value.
Do I Need Planning Permission for a Loft Conversion in Barnet?
Most loft conversions in Barnet fall under Permitted Development rights, meaning you don't need full planning permission — provided the conversion meets certain conditions. If your property is in a conservation area, or if you want a mansard conversion, you will need planning permission. We manage the entire process for all our clients.
How Long Does a Loft Conversion Take?
A typical dormer loft conversion in Barnet takes 10–14 weeks from start to finish. We provide a detailed programme at quotation stage so you know exactly what to expect.
Ready to get a quote? Call us on 020 8441 3144, message us on WhatsApp, or use our Online Price Guide to get an instant budget estimate.