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Mansard Roof Cost Calculator

Estimate UK 2026 mansard roof cost by lower-face area, upper-deck area, materials, dormer count, storey and access. Aligns with BS 5534, BS 6229, NFRC Code of Practice, Listed Building & Conservation Areas Act 1990.

Mansard Roof Cost Calculator

Estimate UK 2026 mansard roof cost by lower-face area, upper-deck area, materials, dormer count, storey and access. Lower steep face priced as pitched roofing; upper deck priced as low-slope membrane. Aligns with BS 5534, BS 6229, NFRC Code of Practice, Listed Building & Conservation Areas Act 1990.

Estimated mansard roof cost
£318,080
Range: £270,368 – £381,696
steep lower face + low-slope upper deck + dormers + strip + consent + skip
Lower face
£176,000
Upper deck
£74,400
Dormers
£1,520
Strip out
£40,600
Consent
£0
Skip
£520

What this calculator estimates

This calculator quotes the all-in installed cost for a 2026 UK mansard roof project. It separates the bill into the line items that experienced steep-slope-plus-low-slope contractors actually invoice:

  • Steep lower face (brisis) — pitched-roof material installed on the 65-75° lower section, priced as steep-slope roofing at roughly 2× the per-m² rate of a standard 30° pitched slate roof.
  • Flat upper deck (terrasson) — single-ply membrane or traditional lead installed on the 5-10° upper section.
  • Dormers — per-dormer flashing scope including step flashing, head flashing, side flashing and curb saddles.
  • Strip-out — removal of the existing mansard covering (both sections).
  • Consent — Listed Building Consent or Conservation Area Consent application costs.
  • Skip / disposal — skip hire and tip fee.
  • Weekend / out-of-hours premium — applied for occupied buildings requiring restricted working hours.

A minimum call-out fee of £1,500 applies for most UK mansard projects.

How to use it

  1. Measure the brisis area in m² — building perimeter × vertical break height × 1.06 (70° slope factor).
  2. Measure the terrasson area in m² — roughly the building footprint minus the brisis footprint projection.
  3. Pick the lower-face material — slate is the heritage default for most Listed and Conservation Area mansards.
  4. Pick the upper-deck membrane — TPO is the modern default; traditional lead for Grade II* and Grade I properties.
  5. Set dormer count — count every dormer protruding through the brisis.
  6. Set storey count — most UK mansards sit on two-storey-plus-mansard terraces.
  7. Pick access tier — typical London terraced mansards require full pavement scaffold (hard access).
  8. Toggle add-ons — strip-out, consent, skip, weekend premium.

Typical 2026 UK mansard roof cost ranges

These reflect 2026 pricing from NFRC’s Q1 2026 Roofing Market Report, Checkatrade 2026 Trade Costs Guide, MyBuilder pricing data, and Q1 2026 contractor quotes from London W1/W2/W8/SW1/SW3/NW3, Edinburgh New Town, Bath, Cheltenham and Brighton — the four UK markets where mansard housing stock is concentrated.

Scope (two-storey base, moderate access, 4 dormers, strip + skip)2026 installed price
Small mansard (90 m² brisis + 70 m² terrasson, slate + TPO)£18,000 – £28,000
Standard mansard (150 m² brisis + 110 m² terrasson, slate + TPO)£30,000 – £48,000
Standard mansard, lead brisis + lead terrasson (Grade II*)£85,000 – £135,000
Standard mansard, zinc standing-seam + TPO£42,000 – £62,000
Large institutional (300 m² brisis + 220 m² terrasson, slate + BUR)£75,000 – £115,000
Slate brisis upgrade over asphalt baseline+85% on lower-face line
Lead brisis upgrade over asphalt baseline+120% on lower-face line
Zinc standing-seam upgrade over asphalt baseline+25% on lower-face line
EPDM vs TPO on terrasson−8% on upper-deck line
Each additional dormer+£380
Strip-out+£14.50 / m² (lower + upper combined)

Add 15% for two-storey access (typical UK terraced mansard), 35% for three-storey or higher, and 10-30% for difficult access (full pavement scaffold + pavement licence).

Cost drivers

Brisis material. Welsh natural slate is the heritage default for most UK Listed mansards — Penrhyn, Ffestiniog, Cwt-y-Bugail, or Welsh equivalent. Spanish slate (Bernardos, San Pedro) is accepted where matching existing on later mansards. Lead sheet at Code 5-6 (2.24-2.65 mm) is the original Parisian/London cladding and is still required on the most prestigious Grade II* and Grade I properties. Zinc standing-seam (VMZINC Pigmento, Rheinzink prePATINA) is accepted where original. Substitution to asphalt strip shingle or fibre-cement slate is typically refused under Listed Building Consent.

Labour premium. Doubles the per-m² rate of a standard 30° pitched slate roof. The premium is structural — Work at Height Regulations 2005 mandate scaffold-with-crash-deck for the 70° face, slate-laying speed drops to 1-1.5 m² per slater per day, and cut-and-fit waste runs 15-20% around dormers.

Terrasson membrane. TPO is the modern industry baseline for non-Listed terrassons (Sika Sarnafil G410-12, IKO Armourplan PSG-PT, Bauder Thermofol U with BBA Agrément). EPDM is the budget single-ply; SBS modified bitumen for any terrasson with roof traffic. On Grade II* and Grade I Listed mansards, traditional lead sheet at Code 7-8 (3.15-3.55 mm) is typically the only acceptable material and runs roughly 2× the TPO cost per m².

Dormer count and complexity. Each dormer carries £350-£500 in flashing scope. Round-top dormers and oeil-de-boeuf windows add £150-£300 each. The dormer cheek is clad in the same material as the brisis.

Strip-out and existing layers. Single-layer strip is £14.50/m². Double-layer (common on 1880s mansards re-roofed in the 1950s) runs £22/m². Triple-layer triggers timber decking inspection and possible deck replacement.

Pavement licence and scaffold. For terraced mansards in central London, scaffold occupies the pavement and requires a Local Highway Authority licence. Typical 2026 rates: Westminster £18-£25 per linear metre per week; RBKC £15-£22; Camden £14-£20. Plan a 4-6 week scaffold-and-licence lead time.

Per-locale data sources

UK figures in this calculator are sourced from:

  • NFRC 2026 Roofing Market Report.
  • Checkatrade 2026 Trade Costs Guide (slating, single-ply, lead sheet, dormer flashing).
  • MyBuilder 2026 pricing data.
  • NSA (National Slate Association) and Welsh Slate producer pricing for natural slate.
  • Lead Sheet Training Academy material pricing for lead sheet at Code 5-8.
  • Sika Sarnafil, IKO, Bauder, Firestone published list pricing for single-ply membrane.
  • BBA Agrément certificates for product compliance.
  • Historic England Listed Building Consent practical guidance.
  • Q1 2026 contractor quotes from London W1/W2/W8/SW1/SW3/NW3, Edinburgh New Town, Bath, Cheltenham and Brighton.

Related UK calculators: slate roof cost calculator, TPO roof cost calculator, flat roof replacement cost calculator, dormer installation cost calculator.

When to call a contractor

UK mansard re-roofing is not a DIY scope. The brisis fall-arrest scaffold requirement is the legal threshold — Work at Height Regulations 2005 require collective fall protection (scaffold with edge protection and crash deck) and CDM 2015 brings the work into the principal contractor regime above 30 person-days. Combine that with Listed Building Consent (for the 70%+ of UK mansards on Listed properties) and pavement licence (for the 50%+ of London terraced mansards on pavement-front buildings) and the practical answer is: appoint a NFRC-member roofing contractor with documented Listed Building and steep-slope mansard experience, request written method statement and risk assessment referencing NFRC Technical Bulletin 13 (lead-to-membrane transitions) and the Lead Sheet Training Academy Manual, and verify their public liability insurance, employer’s liability and CDM principal contractor competence before signing.

Frequently asked questions

How much does a mansard roof cost in the UK in 2026?
A typical UK mansard re-roof in 2026 costs £24,000 to £42,000 for a 260 m² total roof (150 m² steep lower face + 110 m² flat upper deck) with Welsh natural slate on the brisis, single-ply TPO on the terrasson, four dormers, two-storey base, moderate access, full strip-out, Building Control notification and skip. UK mansards are concentrated in London (Belgravia, Mayfair, Kensington, Bayswater, Notting Hill), Edinburgh New Town, Bath, Cheltenham and Brighton. The vast majority are on Grade II Listed or Conservation Area properties, which means slate-replacement-in-kind is the default specification and substitution materials trigger Listed Building Consent or Conservation Area Consent review. Source: NFRC 2026 Roofing Market Report, Checkatrade 2026 Trade Costs Guide, MyBuilder 2026 pricing data, Q1 2026 quotes from London W1/W2/W8/SW1/SW3 and Edinburgh EH1/EH3 postcodes.
Are mansards Listed in the UK?
Most are, yes. The two main UK mansard stocks are: (1) London terraced housing built 1860-1900 in the Italianate and Second Empire revival styles — concentrated in Belgravia, Mayfair, Kensington, Bayswater, Notting Hill, Pimlico, and the Edwardian-era expansion in Hampstead, Chelsea and Marylebone — virtually all of which sit within a Conservation Area and many of which are Grade II Listed. (2) Edinburgh New Town and Bath Georgian-era housing where mansard storeys were added later — Listed Building status applies to the whole property including any later mansard. Roof work to a Listed Building requires Listed Building Consent from the Local Planning Authority; roof work in a Conservation Area where the work is visible from a public highway may require Conservation Area Consent. Slate-replacement-in-kind matching the original colour, size, exposure and detailing is typically fast-tracked; substitution materials (concrete tile, asphalt shingle, fibre-cement slate) are typically refused on Listed properties.
Why does the lower steep face cost so much more per m²?
Three structural reasons. (1) Fall hazard. A 70° brisis is functionally a wall. UK Work at Height Regulations 2005 require fall-arrest scaffold with crash deck plus full edge protection above 2 m, and a brisis triggers the full scope. CDM 2015 also brings the work into the principal contractor / principal designer notification regime above 30 person-days. (2) Installation speed. On a 30° pitched roof a slater can lay 3-4 m² of natural slate per day. On a 70° brisis that drops to 1-1.5 m² per day. Coursing alignment, slate-and-a-half edges and starter courses all take longer. (3) Material waste. Mansard brisis sections typically wrap dormers, corners and curved transitions; slate cut-and-fit waste runs 15-20% versus 8% on a standard pitched roof. The cumulative effect is roughly a 2× per-m² labour premium over an equivalent 30° pitched slate roof in Welsh or Spanish slate.
What materials are acceptable for a UK mansard brisis?
Listed Building Consent and Conservation Area Consent in the UK essentially limit the choice to: (1) Natural slate — Welsh (Penrhyn, Ffestiniog, Cwt-y-Bugail), Spanish (Bernardos, San Pedro), or Brazilian (Microsslate, Caça) where original. Required for most Listed mansard rerooofs. (2) Lead sheet — the original Parisian and London mansard cladding; still permitted and preferred on the most prestigious Grade II* and Grade I properties. Sourced from Calder Lead, Mid-UK Lead, ALM Roofing or Associated Lead Mills. (3) Zinc or copper standing-seam — accepted where original; VMZINC, Rheinzink and KME TECU Classic are the three main suppliers. (4) Plain clay tile — accepted in limited cases (some Edwardian mansards in southern England). (5) Cedar shingle — rare, only on isolated rural mansards. Asphalt shingle, fibre-cement slate, concrete tile and synthetic slate are typically refused on Listed properties and contributing structures in Conservation Areas.
What goes on the flat upper deck (terrasson)?
The terrasson is functionally a flat roof and uses standard UK single-ply membrane systems: TPO (Sika Sarnafil G410-12, IKO Armourplan PSG-PT, Bauder Thermofol U), EPDM (Firestone RubberCover, IKO Spectrasingle, Carlisle Sure-Weld), SBS modified bitumen torch-on (IKO Powergum, Bauder Bakor K5K), or BBA-certified built-up bituminous felt. On Grade II* and Grade I Listed mansards, traditional lead sheet at 8 lb minimum (3.55 mm thick) is the heritage-correct material and the only one allowed by the Local Planning Authority on the most sensitive properties. The brisis-to-terrasson transition flashing is the most important detail — water from the flat deck must be diverted off the front of the brisis without ponding at the transition. NFRC Technical Bulletin 13 covers the principles; specify a Code 5 (2.24 mm) or Code 6 (2.65 mm) lead apron or matching single-ply welded transition flashing.
Do I need scaffold or can I work from a tower?
Mansards almost always require a full pavement scaffold with crash deck. The 70° lower face cannot be safely worked from a mobile tower or roof ladder; Work at Height Regulations 2005 require collective fall protection (scaffold with edge protection) as the first preference, with personal fall arrest only as a fallback where collective protection is not practicable. For terraced mansards in London the scaffold sits on the pavement and requires a pavement licence from the Local Highway Authority — typically £15-£25 per linear metre per week in Westminster, RBKC and Camden, plus deposits. Plan 4-6 weeks lead time for scaffold and pavement licence in central London. The licence cost should be priced into the quote, not absorbed by the contractor.
What is Listed Building Consent and how long does it take?
Listed Building Consent is a separate planning permission required for any works of demolition, alteration or extension to a Listed Building that would affect its character as a building of special architectural or historic interest. It is required in addition to (not instead of) any building regulations approval. Applications are made to the Local Planning Authority (the borough council in London, the unitary council elsewhere) and are typically determined in 8-12 weeks for straightforward like-for-like roof works, longer for changes in material or detailing. Historic England (formerly English Heritage) is consulted on Grade II* and Grade I properties. The application fee is typically £0 for like-for-like slate replacement; £206 for material substitution. Slate-replacement-in-kind matching original colour, size, exposure and detailing is almost always approved; substitution materials are frequently refused on contributing structures.
Can I claim VAT relief on a Listed mansard reroof?
Since 1 October 2012, the zero-rated VAT relief on approved alterations to Listed Buildings has been withdrawn — Listed Building Consent works are now standard-rated at 20% VAT. Two narrow exceptions remain. (1) Substantial reconstruction following a fire or flood may qualify for a reduced 5% rate via VAT Notice 708 section 7. (2) Conversion of a non-residential Listed Building to residential use qualifies for the 5% reduced rate on the construction work. For a typical mansard reroof on an occupied Listed dwelling, 20% standard-rated VAT applies and there is no relief available. The Listed Places of Worship Grant Scheme (HMRC) covers VAT refunds on ecclesiastical Listed Buildings only — domestic Listed mansards are not eligible.

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