Mansard Loft Conversion London and Hertfordshire
The most spacious type of loft conversion — with near-vertical walls that create a room that feels like a full storey. LCCL Construction designs and builds mansard loft conversions across London and Hertfordshire. Full design and build from £45,000. LABC Award Winners 2024. Over 200 reviews rated 4.7 out of 5.
LABC Awards
Winners 2024
200+ Reviews
4.7 / 5 Rating
NFB Members
LABC Partners
What Is a Mansard Loft Conversion?
A mansard loft conversion alters the entire rear roof structure to create near-vertical walls (typically at a 72-degree angle) with a flat roof on top. This creates the maximum possible internal volume and floor space of any loft conversion type, resulting in a room that feels like a full additional storey rather than a converted attic.
Mansard conversions are named after the 17th-century French architect François Mansart and are common across London, particularly on period properties. They are the preferred conversion type when maximum space is the priority and are especially popular on terraced houses where the party wall line allows the full width of the property to be used.
LCCL Construction designs and builds mansard loft conversions across London and Hertfordshire from our base in Finchley, London N3. With over 20 years of experience, 200+ reviews rated 4.7/5 and LABC Awards Regional Winners 2024.
How Much Does a Mansard Loft Conversion Cost?
Mansard loft conversion costs in London typically range from £65,000 to £150,000 depending on the size of the property and the level of specification:
Standard mansard (bedroom + en-suite): £65,000 to £75,000.
Large mansard (two bedrooms + bathroom): £75,000 to £99,000.
Premium mansard (high specification finishing): £99,000 to £150,000.
Mansard conversions cost more than dormer or hip to gable conversions because they involve altering the entire rear roof structure. However, they create the most space and typically deliver the highest return on investment.
Get an instant quote at lcclconstruction.co.uk or call 020 8037 7332.
Subject final drawings, how big the area is, location, finishing, structural drawings, alteration, time when, costs subject to change.
Planning Permission for Mansard Loft Conversions
Mansard loft conversions almost always require planning permission because they significantly alter the roof profile. This is the key difference from dormer and hip to gable conversions, which usually fall under permitted development.
The planning process typically takes 8 to 12 weeks. LCCL Construction prepares and submits the planning application, manages the process and liaises with the local authority on your behalf. We have a strong track record of planning approvals across London boroughs and Hertfordshire councils.
Building regulations approval is also required and is handled as part of our service.
What Is Included?
Full design and build: consultation, measured survey, architectural design, planning application, building regulations, structural calculations, party walls, all construction including complete rear roof rebuild, staircase, electrics, plumbing, plastering, decoration, building control sign-off and optional 10-year LABC warranty.
Areas We Cover
We design and build mansard loft conversions across London and Hertfordshire including Barnet, Finchley, Hendon, Muswell Hill, Highgate, Hampstead, Crouch End, Hackney, Islington, Camden, Clapham, Putney, Wandsworth, Ealing, Southgate, Enfield, Edgware, Borehamwood, St Albans, Potters Bar and surrounding areas. Call 020 8037 7332.
How much does a mansard loft conversion cost?
Mansard loft conversions in London cost £65,000 to £150,000 for full design and build. A standard mansard with bedroom and en-suite typically costs £65,000 to £95,000.
Do I need planning permission for a mansard loft conversion?
Yes, mansard conversions almost always require planning permission because they alter the rear roof profile. LCCL Construction handles the full planning application process.
Is a mansard loft conversion worth it?
Yes. A mansard creates the most space of any loft type and typically adds 15% to 25% to property value. The extra cost compared to a dormer is usually justified by the significantly larger space created.
How long does a mansard take to build?
A mansard loft conversion typically takes 10 to 14 weeks to build. Including planning permission, the full timeline is 6 to 9 months from consultation to completion.
What is the difference between a mansard and a dormer?
A dormer adds a box to the existing roof slope. A mansard replaces the entire rear roof with near-vertical walls and a flat top, creating significantly more internal space.
How do I get started?
Call 020 8037 7332, book a free consultation at lcclconstruction.co.uk, or get an instant quote online.