Bay Window Flat Roof

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Stay Safe & Don't Worry About Exact Numbers! There is no need to climb your roof. Simply estimate the dimensions to your best knowledge. I will personally take precise measurements during a free site visit, and the final price will be calculated using the exact same transparent formula.

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5 Yrs System Warranty 25 Yrs Expected Lifespan
The highly recommended choice for long-term peace of mind. I will install a heavy-duty underlay followed by a premium charcoal mineral top sheet. Welding these two layers together creates a thick, impenetrable shield against the harsh British weather. This system is designed to last at least 15 years, keeping your garage bone-dry and secure.
Tecnatorch SBS Torch-On Plain Capsheet Sanded
Tecnatorch SBS Torch-On Mineral Felt Charcoal

Included in Price

Felt drip edge (4 sides Hardboard)
Felt drip edge (4 sides Hardboard)

Installing a hardboard trim around the entire roof perimeter to create sharp, rigid drip edges for the new felt. This solid backing allows the felt to be formed into a neat overhang, rather than a weak curve. It effectively directs rainwater away from the fascia boards and stops water from tracking back underneath the roof. This ensures a clean, professional finish and full perimeter protection.

Included
Bitumen Primer: Material Application
Bitumen Primer: Material Application
Cromar

Applying a bitumen primer is a crucial preparation step before installing the new waterproofing system. This liquid coating seals the existing substrate and locks in any remaining dust. Its main purpose is to create the perfect conditions for the first layer of felt to adhere flawlessly. This guarantees a strong, permanent bond between the treated surface and the felt.

Included
Ladder Access Work (Scaffolding Not Included)
Ladder Access Work (Scaffolding Not Included)

This service includes access using standard ladders or a hook ladder. Many repairs can be carried out efficiently without the need for scaffolding, saving both time and cost. However, safety is always our priority. If site conditions do not allow safe ladder use (e.g. limited space or difficult access), scaffolding may be required and is not included in this price.

Included
Refurbish Existing Lead Flashing
Refurbish Existing Lead Flashing

This service involves a complete restoration of the existing lead flashing. First, the surface is mechanically cleaned using a wire brush to remove oxidation and debris. We then apply Lead Patination Oil, which protects the metal from weathering and prevents white carbonate staining on your roof. Finally, the brickwork joint is cleaned and resealed using a high-quality specialist lead sealant (silicone) to ensure a long-lasting, watertight finish.

Included
Felt drip edge (4 sides Hardboard)
Felt drip edge (4 sides Hardboard)

Installing a hardboard trim around the entire roof perimeter to create sharp, rigid drip edges for the new felt. This solid backing allows the felt to be formed into a neat overhang, rather than a weak curve. It effectively directs rainwater away from the fascia boards and stops water from tracking back underneath the roof. This ensures a clean, professional finish and full perimeter protection.

Included
Bitumen Primer: Material Application
Bitumen Primer: Material Application
Cromar

Applying a bitumen primer is a crucial preparation step before installing the new waterproofing system. This liquid coating seals the existing substrate and locks in any remaining dust. Its main purpose is to create the perfect conditions for the first layer of felt to adhere flawlessly. This guarantees a strong, permanent bond between the treated surface and the felt.

Included
Ladder Access Work (Scaffolding Not Included)
Ladder Access Work (Scaffolding Not Included)

This service includes access using standard ladders or a hook ladder. Many repairs can be carried out efficiently without the need for scaffolding, saving both time and cost. However, safety is always our priority. If site conditions do not allow safe ladder use (e.g. limited space or difficult access), scaffolding may be required and is not included in this price.

Included

Optional Add-ons

Installation of new Code 4 lead flashing (150mm) to create a secure, watertight seal where the roof meets the brickwork. We professionally fit the lead into the masonry joints and apply Lead Patination Oil to the surface. This protective coating prevents natural oxidation and stops white carbonate streaks from staining your new roof. The joints are finished with high-quality specialist lead sealant, which stays flexible and handles temperature changes better than standard silicone. This method ensures a long-lasting lifespan and reliable protection against the weather.

A surcharge for removing old protective stone chippings from the existing roofing felt. Years of weather exposure cause these stones to melt and bond into a solid crust with the underlying bitumen. Removing them requires intensive physical labour to chip and scrape the surface clean. This crucial step ensures the new roof adheres properly.

Replace weakened or failing garage roof joists to ensure the entire structure remains stable and secure. This is necessary when existing timbers are soft from rot, bowing under weight, or compromised by pests. We provide and install new, high-quality timber joists up to 4 metres long. Simply specify the number of joists required; the price is calculated per unit for a complete installation.

Essential when your roof deck is rotten or sagging. We strip all old felt and timber boards back to the bare joists, creating a clean base for reconstruction. Price includes all labour, professional skip hire delivered to your site, and licensed waste disposal fees. No hidden costs for rubbish clearance. Note: This covers removal only; please also add "New OSB Deck Installation" to your estimate to include the new structural boards.

We create a rock-solid foundation using premium 18mm OSB3 moisture-resistant boards, specifically engineered for structural use in the British climate (BS EN 300 standard). These high-performance boards offer superior strength and durability compared to standard chipboard, ensuring a perfectly flat and stable base for your new roof. Each sheet is precision-fitted and securely fastened to the joists to prevent future movement. Note: This service covers new material and installation only.

15 Yrs Warranty 25 Yrs Lifespan

Preparation and Vapour Barrier: A functional vapour barrier is the most critical step. It stops warm, moist indoor air from rising into the insulation, where it would otherwise condense on the colder upper layers of the roof and cause hidden moisture or rot. In many cases, your existing roofing felt can serve as a reliable vapour barrier if it is in good condition. Insulation Laying and Fixing: We install the 100mm insulation boards onto the prepared base. To maintain the integrity of the vapour barrier underneath, we secure the boards using specialized expanding roofing foam. Mechanical fixings are only used in extreme conditions, such as on very tall buildings or highly exposed coastal sites. Edge Reinforcement (Included in Price): Adding insulation raises the overall roof height by 100mm. Therefore, we install new structural timber rafters of the same thickness around the entire perimeter to reinforce the edges. These timbers and their installation are fully included in the price of this item. Fascia Board Adjustment (Not Included): Please note that because the roof profile is raised, new and deeper uPVC fascia boards are almost always required to aesthetically and functionally cover the new height. These boards are not included in this specific item and are quoted separately. Final Waterproofing: Once the insulation is secured, a new protective system is torch-applied directly on top. This consists of a heavy-duty underlay and a final mineral cap sheet that protects the roof from UV radiation.

A surcharge for removing old protective stone chippings from the existing roofing felt. Years of weather exposure cause these stones to melt and bond into a solid crust with the underlying bitumen. Removing them requires intensive physical labour to chip and scrape the surface clean. This crucial step ensures the new roof adheres properly.

Installation of new Code 4 lead flashing (150mm) to create a secure, watertight seal where the roof meets the brickwork. We professionally fit the lead into the masonry joints and apply Lead Patination Oil to the surface. This protective coating prevents natural oxidation and stops white carbonate streaks from staining your new roof. The joints are finished with high-quality specialist lead sealant, which stays flexible and handles temperature changes better than standard silicone. This method ensures a long-lasting lifespan and reliable protection against the weather.

This service involves a complete restoration of the existing lead flashing. First, the surface is mechanically cleaned using a wire brush to remove oxidation and debris. We then apply Lead Patination Oil, which protects the metal from weathering and prevents white carbonate staining on your roof. Finally, the brickwork joint is cleaned and resealed using a high-quality specialist lead sealant (silicone) to ensure a long-lasting, watertight finish.

Estimate Summary

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Bay Window Flat Roof Cost Calculator | Technical Excellence in Sussex

Does your bay window show signs of dampness, peeling paint, or a visible drip? In the coastal climate of Brighton, Hove, and Worthing, bay window roofs are highly exposed to driving rain and sea salt, making them prone to failure. My instant online calculator provides a transparent, itemised estimate for a professional bay window roof replacement. With 18 years of specialized experience, I focus on delivering a high-spec finish that protects your interior and enhances your home’s character.

Small Area, Big Technical Challenges

A bay window roof may be small in square footage, but it is technically demanding. The primary cause of failure is often the interface between the window frame, the masonry, and the roofing membrane. I utilise premium SBS-modified bitumen torch-on systems. These rubberised membranes offer superior elasticity, allowing the roof to expand and contract without cracking—a common issue with older, rigid felt roofs in the UK.

The Anatomy of a Reliable Bay Roof

My technical approach to bay window restoration goes beyond just “changing the felt”:

  • Expert Leadwork & Flashing: We install or refurbish Code 4 lead flashing at the wall abutment, ensuring a permanent watertight seal where the bay meets the main house.
  • Drip Edge Precision: I install solid hardboard trims to create sharp, effective drip edges. This ensures rainwater is directed away from the window frames and prevents rot in the timber work below.
  • Structural Decking Replacement: If the roof has been leaking, the original boards are likely soft. We replace them with 18mm OSB3 moisture-resistant structural decking to ensure a flat, solid foundation.
  • Thermal Upgrade (Warm Roof): To prevent condensation on your bay window ceiling, I recommend a 100mm thermal insulation upgrade, turning your bay into a “Warm Roof” system.

Full Transparency via Your Client Portal

Quality roofing should never be a mystery. Every project includes access to my Secure Client Portal, designed to keep you fully informed from start to finish:

  • Live Photo Logs: I upload high-resolution “before, during, and after” photos. You will see the quality of the hidden layers, the leadwork, and the final seals directly from your phone.
  • Track Your Project: Follow our progress on a visual timeline, so you know exactly when the work is scheduled and completed.
  • Itemised Documentation: Access your detailed estimates, invoices, and warranties anytime in one secure location.

Ready to protect your bay window? Enter the approximate dimensions in the calculator above. I will personally verify all measurements and technical details during a free site visit to ensure your final quote is 100% accurate.