In this article, Tom Raftery, Solar PV Product Manager at Bauder Limited discusses how to combine a green roof, blue roof and PV array - without compromise.

The construction and development of buildings in today’s market is calling for rooftop solutions that include a combination of technologies, maximising the potential of roofs for environmental advantage. The real challenge comes when roof space is limited and positioning technologies adjacent to each other just isn’t possible.

With modern planning conditions, most local authorities require new buildings to include both a green roof and a significant percentage of site sourced renewables; and if the construction is to be sited in a flood hazard area it must also incorporate a viable SuDS with defined allowable discharge rates. Architects are compelled to deliver a win-win scenario where the technologies are each given the full useable roof area. So, is this scenario too difficult to fulfil, or entirely possible?

In this interview, Tom Raftery, Solar PV Product Manager, Bauder Limited talks about how the company is embracing a cohesive stance to offer the ideal scenario of a vegetated biodiverse roof, complete with the full SuDS capability of a blue roof and a viable PV array for maximum renewable energy generation all on the same useable roof space.

Tell us about Bauder’s triple solution that unifies a green roof, blue roof and PV array
“Bauder has a unique solar photovoltaic (PV) mounting system, BioSOLAR, that is specifically designed to allow the combination of biodiverse green roofs and solar PV whilst having the ability to be installed atop our SuDS blue roof void construction.

The PV system utilises the green roof substrate as ballast removing the need for penetrating the waterproofing to secure the mounting units to the roof and ensuring that the entire roof area can be considered a biodiverse green roof. The void structure beneath allows free-flowing multi-directional water movement to specifically engineered outlets that restrict the total allowable water discharge to meet planning requirements.”

What are the significant design considerations?
“The initial step is to understand the weight loading of the attenuated rainwater to meet the project specific discharge rates of the SuDS report as well as including the BioSOLAR green roof loading. From there, more than any other type of flat roof, it is important to avoid, and wherever possible eliminate, penetrations through a blue roof.

Does the vegetation provide any additional benefits to the PV and the blue roof systems?
“The vegetation we recommend is our BauderFlora 3 seed mix which is a broad mix of low growing biodiverse, shade and drought tolerant species. A well vegetated ground cover is important to ensure that the green roof provides the habitat and nectar source it has been designed for, and also prevents erosion of the substrate which would have implications on the solar design and stability.

Installed above the blue roof void construction the vegetation, substrate and vegetation water storage components retain initial rainfall until saturation, at which point the excess will flow into the blue roof void space for delayed evacuation.

What about environmental credentials?
“Modern buildings are required to have as little impact on their surrounding environment as possible. Using a Bauder BioSOLAR blue roof is best practice from all environmental perspectives as it provides habitat creation, reduces the buildings impact on local drainage systems (helping to meet SuDS requirements) and maximises site sourced renewables.

There are very few aspects of a building’s design that can provide as much of a long term positive impact on the surrounding environment as specifying a Bauder BioSOLAR blue roof on new build projects.”

What maintenance does the triple solution require?
“All solar PV systems require maintenance, especially those with vegetation growing beneath them. Possibly the key benefit of the BioSOLAR system is the unique V angle shape of the mounts. This ensures that a strimmer can be run beneath the edge of the panels, quickly cutting back vegetation with no risk to the operatives.

As for the blue roof components, regular checks of the outlets ensure the drainage holes are free of debris or blockages. Inspections should be carried out following any significant storm event, any notable traffic or remedial works as well as following leaf fall during the autumn months to verify leaf litter is not causing obstruction.”

There you have it: green roof, blue roof and solar PV array, constructed together in harmony for mutual benefit. The green roof increases efficiency of the PV modules and the PV modules provide different growing conditions for a greater variety of plant species and sheltered places for insects and small invertebrate, all sitting above a rooftop SuDS.