The green regulations reshaping flat roofing design

^{Perth High School, winner of the 2026 SPRA Award for Sustainability}

The tiered design, ranging from four to six storeys, is an award-winning example of sustainability-focused roofing in practice. An integrated biosolar roof combines high performance photovoltaic (PV) panels with a biodiverse green roof that helps manage rainwater, supports urban wildlife and improves the building’s thermal performance.

The vegetation layer provides natural ballast to weigh down the PV array, eliminating the need for roof penetrations and protecting the underlying roof membrane from damage from the sun. 

It’s a project that demonstrates how flat roofs are no longer a simple passive solution for plant, drainage and waterproofing. They have become active multifunctional infrastructure needed to meet increasingly stringent regulatory requirements on decarbonisation and climate adaptation.

The challenge for designers, specifiers and contractors is keeping track of emerging policies and guidance, and associated funding streams, and ensuring that more complex roofing designs are both functional and compliant.

The EU’s Energy Performance of Buildings Directive (EPBD) requires all new buildings to be optimised for solar energy generation. Any building permit must now include measures to host rooftop solar, even if it doesn’t actually have it, without requiring costly structural modifications later.

From January 2027, solar is being mandated on all new public and non-residential buildings with a floor area over 250m²; and from January 2030 for all new residential buildings and all new roofed car parks adjacent to buildings.

The UK Government is arguably taking an even more ambitious approach. Its Solar Roadmap, published in June 2025, called for a ‘rooftop revolution’ to install 45-47GW of solar on homes and businesses by 2030, up from around 18GW at present. 

The specifics for new builds are being implemented through the Future Homes and Buildings Standards, due come into force on 24 March 2027, updating Part L and Part F of the Building Regulations. 

The headline requirement is for all new dwellings, along with non-domestic buildings, to include on-site renewable electricity generation. In practice, rooftop solar must, as a minimum, cover the equivalent of 40% of the building's ground-floor area using panels with an efficiency of 0.22kWp per m². 

Exemptions to PV requirements apply for buildings over 18m tall, higher-risk buildings, and sites where limitations like heavy shading or complex roof geometry mean a minimum output of 720kWh per year cannot be achieved. 

The 40% target might seem easily achievable, but according to Tom Raftery, sustainability manager at Bauder, by the time space for a green roof, safe access, fire breaks and other mechanical and electrical kit are factored in “that easy target suddenly starts to become difficult to achieve, which puts the emphasis on considering roofing early in design.”

The scheme updates Minimum Energy Efficiency Standards (MEES) for landlords, requiring all privately rented properties, not just new lets, to achieve an Energy Performance Certificate (EPC) rating of C by 2030, up from the current EPC E rating.

The Warm Homes Plan takes a substantially different approach to the ECO4 (Energy Company Obligation) scheme it replaces.

“ECO4 always leaned towards a fabric-first approach, whereas the new scheme is much more levelised, targeting a combination of insulation and fabric measures, plus PV and heat pumps,” says Raftery. ”The renewable generation side of things gets at least equal billing.”

Solar PV scores highly under the scheme, while substantially thicker roof build-ups or build-ups with higher-performing insulation can boost thermal performance by avoiding cold bridging and managing condensation risk. 

Funding also gets a boost under Warm Homes, with a massive £15bn of public money being made available for upgrades up until 2030. This is being provided through a mix of direct grants, low- and zero-interest consumer loans and other green finance mechanisms designed to incentivise private investment.

An initial £1.29bn was provided through the Warm Homes: Social Housing Fund for projects being delivered between 2025 and 2028. A further £5bn is currently available through the local authority-administered Warm Homes Local Grant, designed to support upgrades to low-income households with EPC ratings from D to G. 

Landlords are a primary target group for this funding stream because 51% of private rented stock currently sits below EPC C. The first property in a landlord's portfolio can be fully funded, up to a £15,000 cap, and for every subsequent property the landlord must contribute 50% of the upgrade cost. 

A Consumer Loan Scheme, launching in April this year, will offer 0% interest loans to homeowners who do not qualify for the low-income grant but need help with upfront costs for solar panels, batteries and insulation.

Green roofs are a key strategy to bolster natural habitats and collectively contribute to the creation of pollinator corridors, as butterflies and other pollinators navigate through a city. 

In addition, the industry is coalescing around the new UK Net Zero Carbon Buildings Standard (UKNZCBS), developed by a technical steering group including RICS, BRE, RIBA, CIBSE, IStructE and LETI, which defines ambitious mandatory targets for both embodied and operational carbon based on measured real-world performance. 

These intersecting policies and standards, alongside compliance requirements for fire and moisture, are transforming roofing into one of the most technically demanding aspects of a building.

The potential combination of PV arrays, green roofs, or blue roof systems that manage surface water attenuation, and thicker insulation, demands a greater level of coordination to ensure they all function as intended.

For example, the additional weight of water captured by blue roof systems can impact on structural tolerances, waterproofing performance and insulation continuity. A biosolar installation can impact on fixing strategies and the spread of fire.

Bauder has witnessed a significant increase in both blue roofs and biosolar installations on new builds, which are often installed alongside the mechanical and electrical components for low carbon heat pumps and other equipment. 

Squeezing different systems against each other on a roof can create competition for roof space and increase the importance of early-stage detailed design input. “If you've got a large roof with a range of services, you need to consider fire performance and how these services might interact, along with safe access across the roof for maintenance,” says Raftery. Such access is intended for periodic maintenance only, rather than routine use of the roof.

Other challenges are arising around embodied carbon targets, he notes, as designers look to build with lower carbon structures such as timber. They must therefore rethink structural requirements when a green or blue roof is being installed. 

Similarly, using thicker roof insulation could mean increasing the size of a wall or footing, requiring greater scrutiny of which products have the lowest overall carbon impact on a scheme rather than just focussing on the individual product’s embodied carbon.

Alongside these concerns, the industry is also grappling with a lack of fire standards related to solar PV. Major proposed changes to Approved Document B (Fire Safety) feature specific provisions for incorporating PV systems on roofs, but remain in consultation with implementation not expected until 2029.

The proposals also include requirements for PV panels to be set at a greater distance from walls and roof edges — a constraint that will make the 40% coverage target harder to achieve on many roofs.

In an era of tighter regulation and rising expectations on sustainability, it’s clear the roof can no longer be treated as an afterthought, it should be viewed as a critical high-performance system from the outset.