CIRIA C817 — Blue Roofs: Design, Implementation and Monitoring

The definitive UK guidance on blue roofs

CIRIA C817 is the definitive UK guidance on blue roof design and implementation — the practice of using flat roof structures for stormwater attenuation. Vector Technical Director Ben Hickman was a Key Technical Author of this publication.

Why blue roofs are structurally different

Blue roofs introduce a deliberate design condition where water is retained on the roof membrane for extended periods. The waterproofing membrane must perform as a permanent containment layer — not as a layer that will see occasional weather. The consequence of failure, and the difficulty of investigating it once the system is operational, are both substantially higher than for a conventional flat roof.

What C817 requires for monitoring

• Waterproofing integrity testing prior to overburden installation
• Ongoing monitoring during operational life
• Leak detection systems beneath attenuation layers
• Pre-commissioning electronic integrity testing as a QA step

Once a blue roof is operational, finding a leak by conventional means is essentially impossible. The time to verify the membrane is before water sits on it.

How Vector applies C817 on live projects

Two services apply C817 guidance directly: electronic integrity testing prior to overburden placement, and buried leak location using electrical field mapping for blue roofs that have already failed.

Publication: CIRIA C817 — Blue Roofs: A Guide to Design, Implementation and Maintenance (2021)
Publisher: CIRIA

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