Flat roof dormer

Calculate your estimate

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.

Service Parameters

× =
Enter dimensions to calculate automatically, or enter the total exact area directly.
15 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 Mineral Felt Charcoal
Tecnatorch SBS Torch-On Mineral Felt Charcoal

Included in Price

Tecnatorch SBS Torch-On Plain Capsheet Sanded
Tecnatorch SBS Torch-On Plain Capsheet Sanded
Tecnatorch SBS

This SBS-modified sanded felt is the core component that upgrades your roof to a high-performance dual-layer system. It provides a robust, elasticated base that perfectly bonds with the final charcoal cap sheet for maximum strength. This foundation layer allows the roof to expand and contract safely during UK weather extremes, preventing cracks and leaks. Choosing this system ensures the highest level of durability and long-term peace of mind.

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
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

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.

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

Description Amount
Calculating... ---
Subtotal ---
VAT ---
Estimated Total ---
ℹ️
No commitment: This is a free, non-binding estimate. Clicking the button will add this service to your list. You can then add more services in the cart or review everything before submitting your request.

“html

Flat Roof Dormer Price Calculator | Instant Quotes in Sussex

Worried about leaks or worn-out covering on your dormer roof? Don’t wait weeks for quotes and vague estimates. My unique online calculator generates a detailed, fully transparent quote for repairing or completely replacing your flat dormer roof in just one minute. As an independent roofer working across Sussex—including Brighton, Hove, and Worthing—I personally oversee every project and guarantee the highest quality workmanship. The price you receive is fair and final.

Why Is a Quality Dormer Roof So Important?

A dormer roof may be small, but it’s absolutely crucial for protecting your home. It most often covers a bedroom, office, or children’s room, where even a minor leak can cause extensive interior damage and disrupt your comfort. That’s why I specialise in highly durable, proven systems such as premium SBS-modified roofing felt. This material is designed to withstand the changeable British weather, safely expanding and contracting without any risk of cracking—guaranteeing a 100% waterproof surface for many years to come.

Smart Insulation for Your Dormer: Year-Round Comfort and Savings

A complete roof replacement is the ideal opportunity to install modern 100mm thermal insulation. This solution significantly improves living comfort in the room beneath the dormer—keeping it pleasantly cool in summer and preventing costly heat loss in winter, which will have a positive impact on your energy bills. My approach ensures the long-term performance and health of the entire structure:

  • Condensation Prevention: A key step is installing a precise vapour barrier that prevents warm, moist air from the interior penetrating the insulation layer. This completely eliminates the risk of condensation, which could lead to hidden rot and mould.
  • Reinforcing the Edge Structure: Adding 100mm of insulation naturally increases the overall roof profile. The price of this service therefore automatically includes the installation of new timber edge components (rafters) to provide solid, stable edges for the new covering.
  • Possible Fascia Adjustment: Please note that due to the increased roof height, it is almost always necessary to install new, deeper uPVC fascia boards to elegantly and functionally conceal the new height difference. You can easily add this item as an optional extra directly in the calculator.

Your Personal Project Hub

I believe in absolute transparency and your satisfaction. That’s why every project includes access to a modern, secure client portal. It’s your personal hub that keeps you perfectly informed at every step:

  • Real-Time Project Tracking: Follow our progress on a visual timeline so you always know exactly what stage the work is at.
  • Real-Time Photo Diary: I regularly upload “before, during, and after” photos directly from your roof, giving you visual proof of the quality of materials and precision of the work.
  • Direct Instant Chat: Got a quick question? Message me directly through the portal. All communication stays neatly organised in one place.
  • Digital Documentation in One Place: Your quotes, deposit receipts, warranties, and final invoices are available online whenever you need them.

Ready to give your dormer the best protection? Simply enter its approximate dimensions in the calculator above. Choose your system, add optional extras like insulation, and watch your detailed quote update instantly.

“