In early 2024, the NHBC revised its Technical Standards, providing updated guidance on ventilation requirements for roof-integrated solar PV systems. Considering this, Marley explains the key considerations for effective and compliant solar PV ventilation solutions, helping roofing contractors to navigate the regulatory landscape.
Legislative updates to Part L of the Building Regulations and the upcoming implementation of the 2025 Future Homes Standard, as well as increasing consumer demand for sustainable energy solutions, are all driving the popularity of renewable energy systems, such as solar PV.
Last year saw the highest level of solar system installation for over seven years, as homeowners took action to reduce their energy bills in the light of the cost-of-living crisis and take advantage of a sustainable energy source to heat and power their homes.
As such, in-roof solar panels are becoming a product of choice for new builds and retrofit roofing projects, as they seamlessly integrate into the roofline, offering both aesthetic appeal and reliable energy output.
Misconceptions
However, despite their growing popularity, there are some industry misconceptions around integrated solar PV roofing solutions. Some believe that these systems limit ventilation, potentially leading to heat accumulation and reduced panel performance. However, the latest updates from the NHBC aim to dispel confusion and reinforce the effectiveness and compliance of integrated solar PV solutions.
Revised NHBC ventilation standards: what to know, what to consider
The NHBC has introduced significant updates to its Technical Standards, with a focus on ventilation for roof-integrated solar PV panels.
As solar PV gains further traction in the construction industry, these changes sought to address the critical relationship between ventilation, energy efficiency and moisture control in roofing systems and deliver much-needed clarity for architects, builders and roofing contractors alike.
The updates clarify key considerations around moisture management, energy efficiency and roof design and outline how contractors can continue to comply with modern standards for integrated solar systems when embarking on roofing projects.
The revised NHBC standards clause 7.2.15, “Ventilation, vapour control and insulation”, means roof coverings with integrated solar panels should now be classified as air impermeable, unless the manufacturer can demonstrate otherwise. This change reflects the need for enhanced ventilation strategies to prevent condensation, while maintaining effective airflow throughout the roof.
These updates align with British Standard (BS) 5250:2021, which provides guidance on moisture control in buildings and emphasises the importance of treating integrated systems as part of the overall roof design.
>>For more insightful articles read more in the January 2025 issue!
For many integrated solar PV panels, the NHBC advises that traditional roof ventilation strategies, such as ridges, eaves and tile ventilation, are generally sufficient to maintain airflow and manage moisture, without requiring additional counter battens.
New ventilation guidelines
Meeting the new NHBC standards and BS 5250 for ventilation depends on the specific roof build-up, and whether it’s a cold, warm or hybrid roof, for example. Key considerations include:
Cold roofs with non-permeable underlay:
- Eaves ventilation: 10,000mm²/m
- Ridge ventilation: 5,000mm²/m
Cold roofs with vapour-permeable underlay:
- Eaves ventilation: 7,000mm²/m for standard ceilings or 3,000mm²/m for well-sealed ceilings.
- Ridge ventilation can substitute for eaves ventilation in well-sealed ceilings.
Warm roofs:
- Eaves ventilation: 25,000mm²/m
- Ridge ventilation: 5,000mm²/m
- A vapour control layer (VCL) on the warm side of insulation.
Compliance answers for the roofing sector
Marley’s SolarTile® system has been specifically designed to simplify compliance for the important NHBC and BS 5250 standards. As an innovative, integrated solar PV solution, it combines energy generation with weatherproof roofing, negating the need for additional counter battens to improve airflow or reduce risk of overheating.
Marley also offers a comprehensive range of products to ensure the entire roof system works together seamlessly, including high-performance underlays with both vapour-permeable and non-permeable options. Ventilated dry ridge and eaves systems, designed for seamless installation, optimal airflow and tile vents, providing aesthetic solutions for supplementary ventilation, are also available.
SolarTile®, combined with Marley’s extensive range of roofing solutions, ensures that those working on new properties or retrofitting existing homes can easily meet the demands of sustainable construction, while delivering superior performance and design. Each component of the Marley roof system is covered by a 15-year warranty, providing additional reassurance for contractors.
The updated NHBC standards support the practical requirement to integrate solar panels into roof systems, while maintaining optimal moisture management and energy efficiency. With clear guidance on ventilation, contractors can install roof-integrated solar panels without compromising roof integrity or performance.
