Skip to content

Mansard Roof

Steep lower slope with a flatter top — maximises attic space

A mansard roof has four sides, a steep lower slope (almost vertical) and a flatter upper section. It's designed to maximise usable space, which is why it's very common in dense urban areas like London.

Common Damage

1. Tile or Slate Damage (Lower Slopes)

  • Cracked, slipped, or missing tiles
  • Steep angle means wind exposure is higher
  • Can quickly lead to leaks

2. Flat Top Section Issues

  • Ponding water
  • Membrane wear
  • Cracks and leaks — similar problems to flat roofs

3. Dormer Problems

  • Mansard roofs often include dormer windows
  • Leaks around dormer edges and seals

4. Flashing Failure

  • Critical around dormers, chimneys, and junctions between slopes
  • One of the most common causes of leaks

5. Structural Movement

  • Over time, the complex structure can shift or sag

6. Timber Rot

  • Water ingress can rot rafters and supports

7. Insulation Problems

  • Older mansard roofs may have poor insulation
  • Leads to heat loss and condensation issues

Repairs

minor Repairs

  • Replace broken tiles or slates
  • Reseal flashing
  • Fix small leaks
  • Repair dormer seals

moderate Repairs

  • Replace sections of flat roof membrane
  • Repair dormer structures
  • Replace underfelt or battens in areas

major Repairs

  • Large-scale retiling of steep slopes
  • Rebuild dormers
  • Replace structural timber
  • Fix sagging or movement

New Installation

When Replacement Is Needed

  • Roof is ageing (often 30–50 years depending on materials)
  • Persistent leaks across multiple areas
  • Structural issues or major renovation
  • Loft conversion or adding living space

Installation Steps

  1. Remove Existing Roof

    • Strip tiles/slates and flat roof materials

  2. Inspect Structure

    • Check rafters, joists, and dormer framing
    • Replace damaged timber

  3. Construct the Frame

    • Build steep lower slopes
    • Create flat or low-pitch top
    • Frame dormer openings

  4. Add Layers

    • Breathable membrane
    • Battens
    • Insulation (very important for living space)

  5. Install Roof Covering

    • Lower slopes: slate, clay, or tile
    • Top section: flat roof system (felt, EPDM, or fibreglass)

  6. Install Dormers & Windows

    • Fit windows and seal properly
    • Add flashing around all openings

  7. Finish Details

    • Ridge and edge detailing
    • Flashing at all joints
    • Gutters and drainage system

Lifespan

Slate / Tile (lower slopes)
50–100 years
Flat Roof Section
10–30 years
Structure
100 years if maintained

Warning Signs

  • Leaks (especially near dormers)
  • Damp or condensation in loft rooms
  • Loose or missing tiles
  • Cracks or sagging
  • High energy bills (poor insulation)

Other Roofing Services

View all roof types

Need Help With Mansard Roof?

Get in touch for a free, no-obligation quote. We'll survey the job and talk you through the options.

Get Your Free Quote