When designing flat roofs for commercial and public sector buildings, there’s increasing pressure to deliver more than just weatherproofing. Roofs are now expected to generate energy, manage stormwater, and support biodiversity — all within the same footprint.
That’s where biosolar roofs come in.
A biosolar system combines two proven technologies — green roofing and solar photovoltaics (PV) — into one intelligent, multi-functional roof build-up. It’s a design approach that maximises roof space and delivers multiple sustainability benefits in one system.
But how does biosolar actually work? What are the advantages? And what should you consider when specifying one?
Let’s break it down.
Biosolar Roof: Simple Definition
A biosolar roof is a flat roof system that integrates a green roof (vegetation layer) with solar PV panels, typically mounted on a frame that sits above or within the planting substrate. The key idea is to combine the benefits of both systems in a way that’s technically compatible, long-lasting, and compliant with building regulations.
Instead of choosing between a green roof or a solar array, biosolar lets you have both — and often, they enhance each other.
How Does a Biosolar System Work?
In a biosolar system:
- A green roof layer (usually sedum or wildflower) is installed on top of a high-quality waterproofing membrane
- Solar PV panels are mounted on a frame that sits within or just above the green roof substrate
- The frame is often ballasted by the green roof substrate itself, removing the need for roof penetrations
- Drainage, water retention, and vegetation growth are all maintained alongside power generation
Importantly, the PV mounting system must be compatible with the green roof supplier and waterproofing manufacturer, to avoid warranty issues or long-term performance problems.
Key Benefits of Biosolar Roofs
A well-designed biosolar roof delivers multiple benefits:
1. Maximises Roof Space
Many buildings only have one viable roof area. Biosolar allows you to get renewable energy and green infrastructureon the same surface, without compromise.
2. Improves PV Efficiency
Vegetation on the roof helps to cool the ambient temperature, reducing heat stress on the solar panels. This can improve energy yield during warmer months, especially compared to panels installed directly onto hot membranes.
3. Supports Biodiversity and Urban Cooling
The green roof component attracts pollinators and helps reduce the urban heat island effect — important for BREEAM, Net Zero, and biodiversity net gain targets.
4. Reduces Rainwater Run-Off
Green roof layers provide attenuation and filtration, which is valuable on buildings that need to comply with SuDSrequirements or manage drainage discharge rates.
5. Avoids Roof Penetrations
Most biosolar systems use ballasted frames that sit within the green roof build-up. That means no drilling or fixing into the waterproofing, reducing both installation risk and long-term maintenance needs.
Where Are Biosolar Roofs Commonly Used?
Biosolar is ideal for:
- Schools and universities
- Public buildings and NHS estates
- Local authority assets
- Commercial and office developments
- Retrofit projects aiming to enhance sustainability and meet Part L or ESG targets
It’s particularly valuable on buildings where space is limited, or where clients want to hit multiple sustainability goals without extending the building’s footprint.
What to Consider When Specifying Biosolar
To make biosolar work in practice, good early-stage planning is essential. Here’s what to factor in:
- Waterproofing Compatibility: Make sure the mounting system is approved by the green roof and membrane manufacturer — this protects warranties and avoids compliance issues.
- Weight Load: Green roofs and ballasted PV systems can add significant load. A structural engineer should always assess the roof’s load-bearing capacity.
- Planting Type and Height: Low-maintenance sedum is common, but taller planting can cause unwanted shading on the PV panels — design the layout to optimise sunlight exposure.
- Maintenance Access: You’ll need to allow for safe access to both the panels and vegetation. Maintenance plans should cover both solar cleaning and green roof health checks.
- Fire Safety: Biosolar systems must be designed in accordance with RC62, GRO fire risk guidance, and any site-specific requirements (e.g. firebreaks, PV panel clearances, non-combustible substrates).
PV Plus: Your Biosolar Installation Partner
At PV Plus, we specialise in delivering biosolar installations on commercial flat roofs. We’ve worked with leading roofing systems like Axter, Bauder, and Sika, and understand the importance of integrating solar, waterproofing, and green roofing into one cohesive, compliant solution.
We handle:
- Design coordination with your green roof and waterproofing supplier
- Installation using approved biosolar mounting systems
- Compliance with fire safety, drainage, and warranty requirements
- Maintenance plans for both vegetation and PV performance
If you already have a green roof and want to retrofit solar, we can also assess your build-up and recommend a compatible biosolar option.
Biosolar System Providers
Several leading roofing manufacturers now offer integrated biosolar solutions that combine green roof technology with solar PV mounting systems. Two standout providers in the UK are Axter and Bauder, both of whom have designed specialist systems for flat roof environments where structural loading and waterproofing integrity are critical.
Axter Biosolar System
Axter’s Biosolar system is a fully integrated solution that combines their waterproofing systems with solar PV supports and green roof layers. It’s a non-penetrative, ballasted design that uses the weight of the green roof and bespoke concrete footings to secure the PV array without compromising the waterproofing. The system is compatible with Axter’s hot melt, bituminous, and synthetic membranes, making it highly versatile for retrofit and new build projects. It’s particularly suited to schemes where planning requires both ecological and renewable benefits, such as schools, public buildings, and large-scale commercial developments.
Key features:
- Non-penetrative and fully integrated with Axter membranes
- Suitable for extensive green roofs
- Pre-engineered system to meet wind and load calculations
- Designed for long-term roof performance and low maintenance
Bauder Biosolar System
BauderSOLAR G LIGHT is Bauder’s lightweight biosolar PV mounting system that’s designed to work seamlessly with their green roof build-ups. The system uses a unique support board with pre-installed metal rails, which allows the PV modules to be fixed securely without penetrating the waterproofing layer. It’s especially valuable where roof load capacity is limited, as the system spreads weight evenly and avoids point loading. BauderSOLAR G LIGHT is compatible with Bauder’s bituminous and root-resistant waterproofing systems, ensuring full system warranty coverage when installed together.
Key features:
- Lightweight design ideal for sensitive or weight-restricted roofs
- Non-penetrative mounting protects waterproof integrity
- Fully compatible with Bauder green roof and waterproofing systems
- Covered under Bauder’s single-point guarantee when installed as a full system
Final Thoughts
Biosolar systems offer a smart, future-proof way to meet the complex demands placed on flat roofs today — from carbon reduction and biodiversity to energy efficiency and planning compliance.
Whether you’re designing from scratch or upgrading an existing roof, biosolar helps you do more with the space you have. And with the right partners in place, it can be delivered with confidence.
Got a biosolar project in mind? Get in touch with the team at PV Plus — we’ll help you get the technical details right and the long-term results you’re looking for.
