Crumlin, Caerphilly: Large-Scale B Roof(t4) Certified Modular Green Roof Installation

This extensive green roof project in Crumlin, Caerphilly, South Wales, covered more than 1,200 square metres and was delivered in collaboration with Polyroof / Roberts Manufacturing. Originally specified as a traditional rollout green roof, the scheme evolved following fire compliance concerns raised by the project architect.

Wallbarn was able to provide full reassurance that its M-Tray® modular green roof system had undergone physical fire testing and achieved B Roof(t4) certification — offering confirmed compliance with current UK fire safety regulations.

This assurance, combined with the system’s technical advantages, ultimately led to a change in specification.

From Rollout to Modular: A Smarter Specification

The original design called for a rollout green roof system. However, on a project of this scale — particularly on a pitched roof — fire compliance and long-term performance were critical considerations.

Wallbarn demonstrated that M-Tray® not only met the required fire standards but also offered additional practical benefits:

• B Roof(t4) certified through physical fire testing

• Modular trays that can be lifted individually for maintenance

• Faster installation compared with rollout systems

• Improved long-term flexibility and futureproofing

The ability to remove and replace individual trays without disturbing the wider roof was particularly appealing to the design team. This modular advantage, alongside confirmed fire certification, led the architect to revise the original specification in favour of M-Tray®.

Managing a Large Pitched Roof

With over 1,200m² to cover, and the roof incorporating pitched sections, structural detailing was crucial.

Wallbarn advised the installation of horizontal battens and structural parapets to prevent potential slumping. On a roof of this size, the weight of a traditional rollout system across a pitched surface can create:

• Slippage over time

• Membrane stress at edges

• Uneven load distribution

By integrating appropriate structural details into the build-up, the risk of movement was mitigated from the outset.

These elements were carefully incorporated into Polyroof’s Protec liquid waterproofing system, ensuring that membrane integrity was fully maintained. The coordination between the green roof system and waterproofing solution was critical to delivering long-term reliability.

Precision Logistics in a Constrained Location

Logistics played a major role in the project’s success. The site was located within a busy industrial estate with restricted access — no road closures were permitted, and there were no dedicated loading bays.

More than 5,000 M-Tray® modules were required to complete the installation.

To manage this efficiently, Wallbarn developed a tightly controlled four-week delivery programme:

• Trays were harvested and loaded in batches of 640

• Three articulated lorry loads were dispatched each week

• Deliveries were scheduled in strict sequence to match installation progress

Nia from Wallbarn’s Logistics Department maintained continuous communication with:

• Haran Roofing

• Polyroof

• The appointed transport provider

This proactive coordination ensured each delivery arrived on time, minimising site congestion and keeping the programme on schedule.

Efficient Installation and Long-Term Benefits

Thanks to the modular format of M-Tray®, installation progressed quickly once materials reached the roof. Each tray clicks into place using an interlocking system, creating an instant, seamless green roof surface.

The benefits of this approach include:

• Immediate visual impact

• Reduced installation time

• Simplified future maintenance access

• Improved long-term structural stability

Unlike rollout systems, which may require significant disruption for future inspections or repairs, modular trays can be lifted individually to access underlying services or membrane areas.

A High-Performing, Award-Nominated Scheme

The completed green roof delivers:

• Verified B Roof(t4) fire compliance

• Structural security across pitched sections

• Long-term membrane protection

• Enhanced environmental performance

The client, along with Polyroof and Haran Roofing, expressed strong satisfaction with both the process and the finished result.

The project has since been nominated for multiple roofing and landscaping awards, reflecting the exceptional planning, collaboration and technical excellence demonstrated throughout.

Delivering Compliance, Performance and Confidence

This Crumlin, Caerphilly scheme highlights how early technical engagement and collaborative problem-solving can transform a challenging specification into a fully optimised solution.

By combining certified fire performance, structural detailing expertise and meticulous logistical coordination, Wallbarn delivered a modular green roof system that met regulatory demands, installation constraints and long-term performance expectations without compromise.

The result is a large-scale, futureproofed green roof that sets a benchmark for complex commercial installations across the UK.

To view the full case study, please click here.