How Much Does a Loft Conversion Cost in London in 2026?
- Lccl Construction
- 6 days ago
- 3 min read
A loft conversion in London typically costs between £30,000 and £70,000 in 2026, depending on the type of conversion, the size of the property, and the level of finishing required. At LCCL Construction, our loft conversion prices start from £18,000 for a basic Velux conversion and go up to £75,000 or more for a large mansard or L-shaped conversion with full design and build.
What Affects the Cost of a Loft Conversion?
Several factors determine the final price of a loft conversion in London. The type of conversion is the biggest factor — a simple Velux loft conversion with roof windows is the most affordable option, while a mansard conversion that changes the entire roof structure costs significantly more. The size of the property matters too, as a terraced house in North London will have different structural requirements to a detached home in Hertfordshire.
Other cost factors include the current condition of your roof, whether you need planning permission, party wall agreements with neighbours, and the quality of internal finishing such as bathrooms, flooring and lighting.
Loft Conversion Prices by Type in London (2026)
Here is a general guide to loft conversion costs in London and Hertfordshire:
Velux Loft Conversion: £18,000 to £30,000. This is the simplest option where roof windows are installed without altering the roof structure. It works best when you already have good head height in the loft.
Dormer Loft Conversion: £30,000 to £50,000. A dormer extends outward from the existing roof slope, creating additional floor space and headroom. This is the most popular type of loft conversion in London.
Hip to Gable Loft Conversion: £35,000 to £55,000. This involves extending the sloped side of a hipped roof to create a vertical gable wall, significantly increasing usable space. Ideal for semi-detached and detached houses.
L-Shaped Loft Conversion: £40,000 to £60,000. An L-shaped dormer extends across two planes of the roof, creating the maximum amount of additional space. Popular for terraced houses in London.
Mansard Loft Conversion: £45,000 to £75,000. This replaces one or both roof slopes with near-vertical walls and a flat roof on top. It creates the most space but usually requires planning permission.
Does a Loft Conversion Need Planning Permission?
Most loft conversions in London fall under permitted development rights, meaning you do not need planning permission. However, mansard conversions and conversions in conservation areas typically do require planning permission. At LCCL Construction, our design and build service includes handling all planning applications on your behalf.
How Long Does a Loft Conversion Take?
A typical loft conversion takes between 8 and 12 weeks to complete once construction begins. The full design and build process, including architectural drawings, planning applications and building regulations approval, usually takes an additional 6 to 10 weeks before construction starts.
How Much Value Does a Loft Conversion Add?
A well-designed loft conversion can add between 15% and 25% to the value of a London property. For an average London home valued at £500,000, that could mean an increase of £75,000 to £125,000 — significantly more than the cost of the conversion itself.
About LCCL Construction
LCCL Construction is a design and build company based in Finchley, London N3, specialising in loft conversions and house extensions across London and Hertfordshire. With over 20 years of experience and a 4.7-star rating out of 5 stars rating on Trustpilot, Reviews io, Yell, LCCL Construction Reviews from 200 reviews, we handle everything from architectural design and planning permission through to construction and finishing. Contact us on 020 8037 7332 or visit lcclconstruction.co.uk for a free consultation and instant quote.
