CIRIA Blue Roofs: Ensuring Your Roof is Watertight

Building a property with a blue or green roof is a fantastic way to contribute to a sustainable future. These roofs not only look great but also offer environmental benefits like improved drainage and reduced energy consumption. However, like any construction project, it’s crucial to understand the potential pitfalls, especially when it comes to waterproofing. The Construction Industry Research and Information Association (CIRIA) provides guidance to help you avoid common mistakes and ensure your roof is built to last.

British Standards and Waterproofing

In 2009, British Standards (BS 8102: 2009) were updated to address the significant impact of human error on waterproofing failures. This standard now requires that any waterproofing survey includes three key points before delving into the specifics of water ingress in basements:

• Human and mechanical errors in manufacturing
• Human errors during system application
• Human errors in design and material selection

CIRIA’s C817 guide expands on these points, offering practical advice on how to mitigate these risks during the design and construction of blue roofs. 

This guide is particularly relevant for ensuring the integrity of latent defects warranty insurance, which is often required by major structural warranty companies in the UK.

Importance of Quality Assurance and Repairability

To ensure a successful blue roof installation, quality assurance is paramount. CIRIA recommends that a suitably trained, competent, and independent third party, such as a member of the Roof and Waterproofing Test Association (RAWTA), should provide quality assurance. 

The waterproofing designer should specify the recommended quality assurance test procedures within their design. This may include:

• Electronic integrity testing (for conductive substrates)
• Flood testing
• Adhesion testing2

Visual inspections should be conducted at every stage of the waterproofing application before covering up the waterproofing layer. Any defects found should be repaired by the waterproofing contractor and retested.

Detailed reports should be issued to the installer and other relevant parties.

If potential damage occurs during the installation of overburden or follow-on trades, the independent third party should revisit the site, reinspect, and update the reports.

Repairability is another key aspect to consider. The blue roof waterproofing design should facilitate easy defect location to ensure repairability, as recommended by BS 8102:2022.

Using monolithic structural substrates and fully bonded waterproofing simplifies defect location. For other waterproofing systems or build-ups, consider using permanent leak detection systems.

Testing and Inspection Checklist

Before handing over the waterproofing system, an independent third party like RAWTA, or an accepted equivalent, should test it to confirm its integrity.

In line with BS 6229:2018, the roof support structure should undergo testing to ensure there are no backfalls. A level survey is recommended, and if backfalls are identified, remedial action should be taken before installing the roof waterproofing.

Quality assurance may include the following:

• Visual inspections
• Electronic (for conductive materials) leak detection
• Vacuum testing
• Hydraulic tests
• Adhesion tests
• Potential load testing
• Flood testing (where possible)

By adhering to CIRIA’s guidance and implementing these quality assurance measures, you can ensure your blue or green roof is built to the highest standards, providing you with peace of mind and a watertight investment.