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What changes the cost of a bay window roof?
A bay window roof quote depends on whether the top is flat or pitched, what it is covered with, how the roof meets the house wall, and how much timber underneath has rotted. This guide does not print a whole-job price, but it lists some material prices the Federation of Master Builders publishes.
Last reviewed:What is a bay window roof?
A bay window sticks out from the front or side of a house, and it needs its own small roof to keep the rain out. On a single-storey bay that roof sits just above the window head. On a two-storey bay it sits above the upstairs window, sometimes joining the main roof.
Because the roof is small, people expect a small price. In practice the work is fiddly. There are tight corners, short runs of covering, a join to the house wall, and often rotten timber hidden under the old covering. Access can also be awkward, especially over a front garden or a path.
This guide explains what a roofer looks at before pricing a bay roof, and what a clear quote should say. It does not print a whole-job price. Our roofers page covers the trade, and the roof repair cost guide explains wider repair pricing.
QuoteZila begins in Cheshire, with Crewe, Nantwich and Sandbach first, and anyone in the UK can post a bay roof job.
Flat top or pitched top?
Flat-topped bays are common on many houses. The top is a small, nearly flat deck of boards on short joists, covered with lead, roofing felt, a rubber membrane or a fibreglass layer. A flat top drains to one edge, often into a short gutter.
Pitched or hipped bays have small sloping faces covered with tiles or slates, with a little ridge and hip tiles where the faces meet. They look like a miniature version of the main roof, and they need the same parts: battens, underlay, tiles and lead at the wall.
Canopy bays have one roof running across the bay and a front door or porch beside it. One quote may cover both.
The type you have sets most of the price. A flat lead top is mainly skilled leadwork. A tiled hipped top is mainly carpentry, tiling and flashing. If you are unsure which you have, a clear photo from the street is enough for a roofer to tell.
What do the materials cost?
The Federation of Master Builders publishes material prices in its flat roof guide, and some apply to a flat-topped bay. These are material prices only, not a quote for your bay.
| Item | FMB material price | Why it matters on a bay |
|---|---|---|
| OSB deck board | Around £25 per board [S1] | Rotten decking under the old covering has to be replaced |
| Lead flashing | Around £25 for a three metre strip [S1] | Seals the join between the bay roof and the house wall |
| Edge trims | £10 to £20 per 2.5 m length [S1] | Finishes the edge of a felt or membrane top |
| Labour share | Around 40% of a flat roof replacement total [S1] | On a small roof, time and access can outweigh materials |
| Contingency | Budget an extra 10 to 15% [S1] | Hidden rot is common under old bay coverings |
| VAT | Registration is required above £90,000 of taxable turnover in the last 12 months [S6] | Totals must compare like with like |
The FMB guide is written for whole flat roofs, not bays, so treat these as building blocks rather than a price for your job [S1].
What else changes a bay roof quote?
The covering. Lead, felt, rubber membrane, fibreglass, tiles and slate all need different skills. Ask the roofer why they recommend one over another for your bay.
Like for like or a change. Replacing lead with lead keeps the look. Swapping to a membrane can change it. On a pitched bay, changing from slate to tiles changes the weight, and Planning Portal says a new covering that increases the weight of the roof covering by 15 per cent or more needs approval [S2].
Rotten timber. The boards and the short joists under a bay roof often rot where water has sat for years. A roofer cannot see this until the old covering is off, so a clear quote names a rate for replacing any rotten timber found.
The wall flashing. Where the bay roof meets the house, the flashing should be tucked into a mortar joint and dressed down over the roof. A new covering with an old, split flashing will still leak.
Gutters and drips. A flat top drains to an edge. If the edge trim, drip or gutter is wrong, water runs back onto the window frame or down the brickwork.
Access. A ground-floor bay may be reachable from a platform or a small tower. A two-storey bay over a path may need scaffolding. Ask how access is priced and who arranges it.
Is the bay itself sound?
Sometimes a leaking bay roof is a symptom, not the cause. If the bay has dropped, the window frames are distorted, or there are cracks running from the corners of the bay into the house wall, the bay structure may have moved.
That is not a roofing repair. It needs a builder and possibly a structural engineer to look at the support over the window and the bay foundations. This guide does not give a method for checking or propping a bay. Put any cracks and sticking windows in your job, so the right trade comes out first.
If the bay windows themselves are failing, our uPVC bay window quote guide covers that job. Planning Portal says building regulations have applied to all replacement glazing since 1 April 2002 [S3]. You can use an installer registered with a competent person scheme, or seek approval from a building control body [S3]. Doing the roof and the windows together can save setting up access twice.
Should the bay roof be insulated at the same time?
The ceiling inside a bay is often the coldest part of the room, because only a thin roof sits above it. When the covering comes off, there is a chance to add insulation above the deck or between the joists.
Planning Portal treats a roof as a thermal element and says work to re-cover a roof should also include improving its thermal insulation [S8]. It also says that if a flat roof with integral insulation is replaced, you may be required to upgrade the insulation [S8]. On a small bay, extra insulation can raise the roof level slightly, which affects how it meets the window head and the wall flashing.
Ask each roofer whether they plan to insulate, how thick the new build-up will be, and how they will finish the edges so the bay still looks right from the street.
Why is this not a DIY job?
Even a ground-floor bay roof is above head height, and leaning a ladder against a bay window is a poor idea. HSE's guidance for workplaces says to avoid work at height where it is reasonably practicable to do so, and otherwise to prevent falls using the right type of equipment [S7]. HSE: work at height. QuoteZila is not affiliated with this organisation. HSE explains more in its introduction to working at height.
This guide does not give steps for working on a bay roof. A roofer will bring suitable access equipment and can look at the whole roof, not just the obvious split.
What should a bay roof quote say?
A clear written quote for a bay roof names:
- the type of roof and the covering to be used, by product or material
- whether the old covering is stripped, and what happens to the waste
- a rate for any rotten boards or joists found once the covering is off
- how the join to the house wall will be flashed
- how water will leave the roof, and whether any gutter work is included
- the access equipment, and whether it is in the price
- any guarantee the roofer offers on the work, in writing
- whether VAT is included
GOV.UK's waste code says that when a tradesperson works on your property, they are responsible for the waste they produce, and the cost of its disposal should be included in what they charge [S5].
Citizens Advice suggests trying to get written quotes from at least 3 different traders, and says some traders charge for quotes, so ask first [S4]. It also says a quote is a fixed price, while an estimate is just a rough guess [S4]. If a roofer asks for a deposit to buy lead or timber, Citizens Advice suggests offering to buy the materials yourself instead [S4].
Jobs you might post
These are examples, not taken from real job posts.
- "Flat lead top over a ground-floor bay leaking where it meets the house wall. Please inspect and quote to repair or replace."
- "Two-storey bay with a small hipped tiled roof. Several tiles slipped and the ceiling inside the bay is stained. Please quote, including access."
- "Felt-covered bay roof over the front door canopy is lifting at the edges. Please quote to re-cover in a longer-lasting material."
Posting a bay window roof job
Add a photo from the street, a close photo of the top if you can take one safely from an upstairs window, and any stains inside. Your job goes to up to five matched local businesses [QZ2]. QuoteZila is free for customers and local businesses [QZ1].
Honest status: QuoteZila is new. We're starting in Cheshire, beginning with Crewe, Nantwich and Sandbach, and growing area by area. Anyone in the UK can still post a job or register a business. How fast you get quotes depends on how many local businesses have joined near you. Businesses can register and receive jobs straight away. We don't check insurance, qualifications or registrations, so please check these yourself before you hire.
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Questions about bay window roof costs
How much does a new bay window roof cost?
This guide does not print a whole-job figure, because bay roofs vary so much. A small flat lead top over a ground-floor bay is a different job from a hipped, tiled roof that runs across a two-storey bay. Ask each roofer to price the covering, the timber, the flashing and the access as separate lines.
Why does my bay window roof leak against the wall?
The join between the bay roof and the house wall is the weakest point. Water usually gets in where the flashing has split, slipped out of the mortar joint or was never dressed properly. A roofer should check that joint before replacing the whole covering.
Can a bay roof be repaired rather than replaced?
Often, yes. A split in a lead top, a lifted felt edge or a few slipped tiles can be repaired if the boards and joists underneath are dry and sound. If the decking is soft or the roof has been patched many times, replacing the covering is usually the longer-lasting choice.
Do I need permission to re-roof a bay window?
Usually not for a like-for-like repair. Planning Portal says repairs or re-covering of an existing roof will not normally need a building control application if less than 25 per cent of the building envelope and less than 50 per cent of the roof is affected. A heavier covering, or any structural change, can need approval.
Does VAT change the price?
It can. A business must register for VAT once its taxable turnover for the last 12 months goes over £90,000. Ask each roofer whether their total includes VAT.
Does QuoteZila check roofers?
No. We don't check insurance, qualifications or registrations, so please check these yourself before you hire. You can report a quote or a business from your job page.
This page is general information, not professional or legal advice. QuoteZila does not check Gas Safe, WaterSafe, NFRC, NICEIC or other registrations against the register on your behalf: look them up yourself.
Part of Cost guides. All services
Related trades
Cost guides
Related pages
- Chimney Flashing: What to Put in a Quote. Lead flashing at a chimney in Cheshire is the joint where the stack meets the covering. This guide prints no price. It shows what the quote must name.
- Chimney Sweep Work in Cheshire: What to Ask. What to tell a chimney sweep in Cheshire: the appliance, how the flue is reached, and when the job is a rebuild rather than a sweep.
Sources
- QZ1: QuoteZila product fact. QuoteZila home and FAQ copy.
- QZ2: QuoteZila product fact. QuoteZila FAQ How does getting quotes work.
- S1: Flat roof replacement cost guide for UK homeowners, Federation of Master Builders. Accessed 2026-11-02. https://www.fmb.org.uk/resource/flat-roof-replacement-cost-guide-for-uk-homeowners.html
- S2: Building Regulations: Work to an existing roof, Planning Portal. Accessed 2026-11-02. https://www.planningportal.co.uk/permission/common-projects/roof/building-regulations-work-to-an-existing-roof
- S3: Doors and windows: Building regulations, Planning Portal. Accessed 2026-11-02. https://www.planningportal.co.uk/permission/common-projects/doors-and-windows/building-regulations
- S4: Before you get building work done, Citizens Advice. Accessed 2026-11-02. https://www.citizensadvice.org.uk/consumer/getting-home-improvements-done/before-you-get-building-work-done/
- S5: Waste duty of care: code of practice, GOV.UK (Defra). Accessed 2026-11-02. https://www.gov.uk/government/publications/waste-duty-of-care-code-of-practice/waste-duty-of-care-code-of-practice
- S6: Register for VAT, GOV.UK. Accessed 2026-11-02. https://www.gov.uk/register-for-vat
- S7: Introduction to working at height safely, Health and Safety Executive. Accessed 2026-11-02. https://www.hse.gov.uk/work-at-height/introduction.htm
- S8: Building regulations: Re-roofing, Planning Portal. Accessed 2026-11-02. https://www.planningportal.co.uk/permission/common-projects/roof/building-regulations-re-roofing