Case Study: Residential Flat Roof Insulation & Waterproofing, Chiswick, London
From failing roof to finished system
The Challenge
A residential property in Chiswick, London, required a cost-effective and long-lasting solution for their ageing flat roof. The existing lead-covered roof was over 25 years old, uninsulated, and showing visible signs of deterioration. The client wanted a turnkey system that would both upgrade thermal performance and restore full waterproofing protection, while avoiding disruptive and costly roof strip-and-replace works.
Duratite-approved contractor, Spray Foam Tech Limited was engaged to install a system that would deliver insulation, waterproofing, energy efficiency, and durability—all within a seamless application process.
Challenges Before Installation
- Ageing Substrate: The original lead roof covering had extensive weathering, patch repairs, and weak points around upstands and rooflights.
- No Insulation: The roof lacked thermal protection, resulting in significant heat loss and cold bridging.
- Waterproofing Risk: Hairline cracks and degraded joints risked water ingress, particularly during heavy rain.
- Access & Disruption: The property was occupied, so the client required a fast installation with minimal disruption or removal of existing coverings.
Project file
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The Solution — step by step
The Solution
Spray Foam Tech Limited used Duratite’s Gaco roofing system for insulation and waterproofing in a single solution:
- Substrate Preparation
- The roof was cleaned, loose debris and vegetation removed, and all cables/fixtures temporarily raised.
- Lead flashings and rooflight edges were detailed to ensure foam continuity.
- Insulation Layer – Closed-Cell Spray Foam
- 25mm of closed-cell spray foam insulation was applied directly over the lead substrate.
- The foam provided an instant thermal upgrade, increasing the roof’s overall energy efficiency and improving occupant comfort.
- Its closed-cell structure created a monolithic barrier, preventing water tracking beneath the surface.
- Protective Coating – GacoFlex S42 Silicone Waterproofing
- Once cured, the foam was sealed with GacoFlex S42, a high-performance silicone roof coating.
- The coating created a seamless, UV-stable waterproofing membrane, ensuring long-term weather protection.
- The S42 system is flexible, able to accommodate building movement, and has exceptional resistance to ponding water.
- System Warranty
- The combined system was installed to manufacturer standards and issued with a 20-year product and installation warranty.
The Outcome
- Turnkey Upgrade: Insulation and waterproofing delivered in one system, avoiding costly roof replacement.
- Thermal Performance: Improved energy efficiency, reducing heat loss and future energy bills.
- Durability: The closed-cell spray foam insulation combined with S42 Silicone ensures long-term resistance to weather, ponding water, and UV degradation.
- Seamless Protection: Spray-applied application eliminated joints, seams, and weak points.
- Fast Installation: Work completed in days with no disruption to the household below.
- Sustainability: By overlaying the existing roof rather than stripping, material waste was minimised.
The Chiswick flat roof was successfully upgraded into a fully insulated, watertight, and future-proofed roofing system. The smooth, seamless silicone finish provided the client with confidence in the system’s 20-year guaranteed protection.
From an aesthetic perspective, the roof now presents a clean, uniform finish compared to the patchy, weathered lead that was previously exposed. Functionally, the property is warmer, more energy-efficient, and safeguarded against water ingress for decades to come.
This project demonstrates how modern spray-applied insulation and coating systems can transform failing flat roofs without the expense of full removal. By combining closed-cell spray foam insulation with the GacoFlex S42 Silicone system, Spray Foam Tech Limited delivered a solution that was cost-effective, sustainable, and high-performing—meeting the client’s goals for comfort, protection, and longevity.
Products used
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