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Overlaying a Flat Roof: A Definition

Overlaying a flat roof is a method to extend a flat roof's lifespan without removing the old roof covering. This process involves installing a new layer of roofing material directly over the existing roof, providing additional protection and waterproofing.


Key Benefits of Overlaying a Flat Roof

  • Increased Lifespan:  Overlaying can add 10 to 20 years to the life of your flat roof, delaying the need for a full replacement.

  • Cost-Effective:  It's generally less expensive than a complete roof replacement, as it saves on labor and material costs associated with removing the old roof.

  • Minimal Disruption:  Overlaying is typically quicker and less disruptive than a full replacement, minimizing inconvenience to building occupants.

Important Considerations Before Overlaying

  • Roof Condition:  A thorough inspection of the existing roof is critical. Overlaying is suitable only if the existing structure is sound and free of significant damage or leaks.

  • Repairs:  Before overlaying, any necessary repairs to the existing roof, such as fixing leaks or addressing structural issues, should be completed.

  • Surface Preparation: The existing roof surface must be clean, dry, and free of debris to ensure proper adhesion of the new layer.

  • Underlying Structure:  The overlay's success depends entirely on the underlying structure's integrity. The overlay may also fail if the original roof fails, voiding any guarantees.

  • Thermal Efficiency and Building Regulations:  Older roofs may not meet current building regulations for thermal efficiency (Part L). Overlaying may necessitate future insulation upgrades, potentially negating initial cost savings.

Expert Advice

While overlaying may seem cost-effective initially, consider the long-term implications. If possible, maintain and repair the existing roof until a full replacement, including insulation upgrades to meet current regulations, is financially feasible.

Key to Success: Proper Application

The success and longevity of an overlay depend heavily on proper installation. This includes:

  • Choosing the Right Material:  The new roofing material should be compatible with the existing roof and suitable for the local climate.

  • Professional Installation:  It's recommended that you hire experienced professionals to ensure the overlay is installed correctly and according to the manufacturer's specifications.

In Summary:  Overlaying a flat roof can be a viable option to extend its life, but it's essential to weigh the potential long-term costs and limitations against the initial savings. Consult with a qualified roofing professional to assess your specific situation and make an informed decision.


As you may be aware, London Flat Roofing is our sister company, which I founded many years ago. We continue to offer comprehensive roofing services. If you're interested in exploring the option of overlaying your flat roof, please don't hesitate to contact us at info@londonflatroofing.co.uk. We're here to help with any questions or services you might need.


In this 2018 video, I walk you through the process of overlaying a flat roof. I demonstrate the essential preparation steps required for some roofs and how a liquid roofing system can be effectively used to overlay an old roof. This guide offers valuable insights for anyone considering roof overlaying as a solution.




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