Mansard Loft Conversion

A mansard loft conversion changes the whole shape of the rear roof, replacing it with a near vertical wall set at a steep angle, usually around seventy two degrees, topped with a flat or gently sloped section. This design creates a large amount of usable space and head height, far more than most other loft conversion types can offer, which makes it popular for homeowners who want a proper full sized extra floor rather than a single added room.

Because a mansard changes the fundamental shape of the roof, it almost always needs full planning permission rather than falling under permitted development. This adds time to the project, usually around eight to twelve weeks for a decision once the application is submitted, but it also allows for a much larger and more versatile finished space.

Mansard conversions are especially well suited to houses with a low, flat roof between two party walls, sometimes called a London roof, which is common across many Victorian and Edwardian terraces. On these properties a mansard can make the difference between a cramped loft and a genuinely spacious top floor.

Who this for

This service is most commonly chosen for Victorian and Edwardian terraced houses with a low, flat rear roof, though it can also suit semi detached and detached properties where a large amount of extra space is the priority. It suits homeowners who are prepared for a full planning application and a longer project timeline in exchange for the largest possible increase in usable space.

Mansard Loft Conversion Cost

A mansard is one of the more expensive types of loft conversion, since it involves rebuilding the whole rear roof rather than adding to what is already there. Current UK prices sit between £1,400 and £2,000 per square metre for a good standard finish, though a simpler specification can come in nearer £1,000 to £1,500 per square metre. For a full project, most mansard loft conversions in the UK now cost somewhere between £50,000 and £80,000, with £55,000 a fairly typical figure nationally. London projects tend to sit at the higher end of that range, often £70,000 or more, largely because of the access challenges that come with working on terraced streets and the higher cost of skilled labour in the capital. The structural work is usually the single biggest cost on a mansard project. Because the rear roof is rebuilt almost from scratch rather than simply extended, the reinforcement of the existing beams and the construction of the new near vertical wall make up a large share of the total price, with labour alone often accounting for around half of what you pay. It is worth remembering that these figures cover the build itself. You will also need to budget separately for the planning application and any design or structural drawings it requires, on top of the party wall agreements mentioned earlier on this page. As with any loft conversion, the only reliable way to know your actual cost is a survey of your specific roof. Get in touch for a free survey and a detailed quote for your property.

Project Process Steps