Converting a flat roof to a pitched roof in 2026 costs £4,000–£8,000 for a small area (garage or single extension) and £8,000–£25,000+ for a full house conversion. A pitched roof lasts 30–50 years compared to 10–20 for most flat roofs, eliminating ponding, leaks, and regular maintenance.
Conversion Costs at a Glance
Garage Roof
Single garage (15–18m²). Timber frame, concrete tiles or slates. 1–2 weeks. The most straightforward conversion — often improves kerb appeal significantly.
Extension Roof
Single-storey rear or side extension (15–30m²). Ties into existing roofline. May need structural assessment if walls need strengthening for the extra weight.
Full House Conversion
Entire house roof (60–120m²). Major project — new roof structure, covering, fascias, soffits, guttering. 3–6 weeks. Often creates usable loft space.
Detailed Cost Breakdown
Garage Flat-to-Pitched Conversion
This is the bread-and-butter job. Most 1960s–1980s houses with attached garages have flat felt roofs that leak, sag, and look tired. Converting to a pitched roof solves all three problems at once.
What's involved: Strip the existing flat roof covering (felt, EPDM, or asphalt), build a new timber roof structure (rafters, ridge board, purlins), install breathable membrane, batten and tile or slate. New fascias, soffits, and guttering to match the house. Typically a 30–40° pitch.
Costs: £4,000–£8,000. The lower end is basic concrete interlocking tiles on a simple gable or lean-to structure. The upper end includes natural slate, lead flashing details, and matching the existing house roof exactly. If the existing walls need a raised wall plate or additional structural support, add £500–£1,500.
Extension Roof Conversion
Flat-roofed extensions from the 1970s and 1980s are notorious for leaking. Rather than re-covering with another flat roof system every 15 years, converting to pitched makes long-term sense — especially if the extension is visible from the street.
What's involved: Same process as a garage, but usually larger area and more complex detailing where the new roof meets the existing house. May need structural calculations if the extension walls weren't designed for the extra weight of a pitched roof (tiles are heavier than felt). The junction with the main house roof is critical — poor flashing here causes leaks.
Costs: £5,000–£12,000. The bigger the extension, the higher the cost. A 4m × 4m extension is straightforward. A 6m × 5m extension with a complex junction to the main house, multiple valley gutters, or a hip-end roof pushes costs up. If the existing flat roof structure is rotten and needs replacing entirely (not just covering), add £1,000–£3,000.
Full House Conversion
Some houses — particularly system-built properties from the 1960s–1970s, and some bungalows — have entirely flat roofs. Converting the whole thing to pitched is a major project but can transform both the appearance and the performance of the property.
What's involved: Complete removal of the existing flat roof structure. New timber roof frame erected (often using pre-fabricated trusses craned into position). Breathable membrane, battens, and tile or slate covering. All new fascias, soffits, guttering, and downpipes. Insulation between and over rafters. Internal work if creating habitable loft space.
Costs: £8,000–£25,000+ for the roof structure and covering alone. A straightforward conversion of a small bungalow (60m² roof area) with concrete tiles sits around £8,000–£14,000. A large detached house (120m²+) with natural slate, multiple hips and valleys, and Velux windows pushes to £18,000–£25,000+. If you're creating a habitable loft room within the new pitched roof, add £8,000–£15,000 for internal works (floor strengthening, insulation, windows, staircase, plastering, electrics).
Why Convert to a Pitched Roof?
Lifespan
A properly built pitched tile or slate roof lasts 30–50+ years. Most flat roofs need replacing every 10–20 years. Over the life of the property, pitched is cheaper.
No More Ponding
Water runs off a pitched roof immediately. Flat roofs pool water (ponding), which accelerates deterioration, finds weak spots, and causes leaks. The number one reason people convert.
Extra Space
A pitched roof creates a void above the ceiling. With sufficient pitch angle and height, this becomes usable storage or even a habitable room — adding genuine floor area to your home.
Additional Benefits
- Better insulation: A pitched roof with insulation between and over the rafters (or at ceiling level) outperforms most flat roof insulation setups. You can achieve 0.15 W/m²K or better, compared to 0.25+ for many existing flat roofs.
- Improved kerb appeal: Flat roofs on houses look dated. A well-matched pitched roof lifts the whole appearance of the property and improves its resale appeal.
- Lower maintenance: No more recoating, repatching, or worrying about every storm. Pitched roofs need an inspection every 5–10 years and the occasional replaced tile. That's it.
- Better ventilation: The void between ceiling and roof covering provides natural ventilation, reducing condensation and damp problems.
Planning Permission & Building Regulations
Planning Permission
Converting a flat roof to pitched almost always requires planning permission. Here's why: the conversion changes the roofline and external appearance of the building, which doesn't fall under permitted development rights for most properties.
What you need:
- Householder planning application: £462 in England (2026)
- Architectural drawings showing the proposed roof — elevations, sections, and street scene
- A design and access statement (your architect usually prepares this)
- Decision timeline: 8 weeks from submission (most straightforward applications)
What planners look at: How the new roof sits in the streetscape, impact on neighbours (overlooking, overshadowing), materials matching the local character, and ridge height. If the new pitched roof significantly increases the height of the building, it's more likely to face objections.
Building Regulations
Building regulations approval is always required for a flat-to-pitched conversion, regardless of planning permission. The building control officer checks:
- Structural adequacy: Can the existing walls support the new roof? A structural engineer's calculations are needed (£400–£800).
- Insulation: The new roof must meet current thermal standards — minimum U-value of 0.16 W/m²K for a roof in 2026.
- Ventilation: Adequate ventilation of the roof void (or warm roof construction if insulating between rafters).
- Fire safety: If creating habitable space in the new loft, fire escape requirements apply.
- Weather resistance: Proper underlays, flashings, and detailing.
Building regulations application cost: £300–£600 depending on your local authority and the scope of work.
Regional Pricing (Full House Conversion)
What Affects the Price
Roof area
The bigger the roof, the more timber, tiles, and labour needed. A 15m² garage roof is a fraction of the cost of a 100m² whole-house roof. Most contractors quote per m² of roof area: £100–£250/m² for the structure and covering.
Covering material
Concrete interlocking tiles: £25–£40/m². Clay tiles: £40–£70/m². Natural slate: £60–£120/m². Fibre cement slate: £30–£50/m². The material choice alone can swing the total cost by £3,000–£8,000 on a house-sized roof.
Roof complexity
A simple gable-end roof is cheapest. Hip-end roofs, multiple valleys, dormers, and changes of pitch add complexity and cost. Each hip end adds £500–£1,500 in extra timber and labour. Valleys need lead or GRP lining (£60–£120/m).
Wall strength
A pitched roof is heavier than a flat roof. If the existing walls weren't designed for the extra load, they may need strengthening — a ring beam (reinforced concrete band along the top of the walls) costs £1,500–£4,000. A structural engineer determines whether this is needed.
Scaffolding
Full house conversions need scaffolding on all sides: £1,500–£4,000 for a standard house, more for larger or complex buildings. Scaffolding on a public footpath needs a licence from the council (£50–£200).
Creating habitable space
If you're turning the new loft void into a room, the internal works add significantly: floor strengthening (£1,500–£3,000), Velux windows (£600–£1,200 each installed), staircase (£2,000–£5,000), insulation, plastering, electrics, and fire safety compliance.
How to Save Money on Your Conversion
💡 Practical ways to reduce your flat-to-pitched roof costs
- Choose concrete tiles over slate. Concrete interlocking tiles cost 40–60% less than natural slate and last 40+ years. They come in a range of colours and profiles to suit most properties.
- Keep the design simple. A straightforward gable or lean-to roof is significantly cheaper than a hipped roof with valleys and dormers. Simple shapes mean less timber, less cutting, and faster installation.
- Combine with other roof work. If the main house roof also needs attention (re-ridging, replacement tiles, new guttering), doing everything in one project saves on scaffolding costs — which are the same whether you're up there for one job or three.
- Use pre-fabricated trusses. For larger conversions, factory-made trusses are quicker to install than site-cut rafters. They're engineered, consistent, and often cheaper once you account for the labour savings.
- Time it for summer. Roof work in winter is slower (shorter days, weather delays) and riskier (exposed building between strip-off and covering). Summer jobs run faster and smoother.
- Get planning sorted first. Don't commit to a builder before planning permission is granted. If it's refused, you've wasted money on detailed construction quotes. Get outline consent first, then price the build.
What Should Be Included in a Quote
A complete quote for a flat-to-pitched conversion should cover:
- Strip-off of existing flat roof — removal and disposal of all existing coverings, insulation, and timberwork
- New roof structure — wall plates, rafters or trusses, ridge board, purlins, bracing
- Breathable membrane and battens
- Roof covering — tiles, slates, or other specified material with all ridge, hip, and verge fittings
- Lead flashings — at all junctions with existing walls, chimneys, and other roof areas
- Fascias, soffits, and guttering — new or replacement to suit the pitched roof
- Insulation — meeting current building regulations standards
- Scaffolding — erection, hire, and dismantling
- Structural engineer's fees — or confirmation that these are excluded
- Building regulations application — or confirmation excluded
- Waste removal — skips for old roof materials
Common exclusions: Planning application fees, architect's drawings, internal loft finishing, decoration of affected ceilings, and satellite dish/aerial relocation.
Hidden Costs to Budget For
Planning Application
Householder planning application in England. Almost always required for a flat-to-pitched conversion. Architect's drawings for the application add £500–£1,500.
Structural Engineer
Calculations to confirm the existing walls can support the pitched roof. May recommend a ring beam or wall strengthening if needed.
Building Regulations
Application and inspections. Required for every flat-to-pitched conversion. The completion certificate is essential for future sales.
Scaffolding
Sometimes quoted separately. Full-house scaffolding for 3–6 weeks. Additional cost if on a public footpath (council licence needed).
Internal Ceiling Repairs
The existing ceiling may need repair or replacement after the flat roof is removed. Replastering and decoration of affected areas.
Temporary Weather Protection
Tarpaulins or temporary roofing while the building is exposed between stripping the old roof and completing the new. Critical in bad weather.
Frequently Asked Questions
Related Cost Guides
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