How holistic roof specification can support compliance with the carbon emissions targets of Part L and the FHS

Marley roof tiles installed on housing estate
Director Roof Systems
Stuart has been working in the construction industry for over 30 years and has spent the last 14 years at Marley.

When it comes to carbon emissions targets for housing, it’s safe to say that requirements are only going to get increasingly rigorous.

Of course, that’s not a bad thing. With the state of the UK’s existing housing stock, the looming climate crisis and increasing levels of fuel poverty across the country, improving energy efficiency is certainly the way forward. The guidance set out in regulations such as Part L and the upcoming Future Homes Standard (FHS), expected in 2025, should help us on our way to that net-zero future that the planet desperately needs.

Sorting through the mass of building regulations, standards and guidelines can be a daunting task, but it’s also a critical one, with the future of the planet and vulnerable lives at stake. The recent raft of new requirements, including the updates to Parts L and F, the new Part O, as well as speculation on the upcoming FHS, means there’s a lot to think about. And that’s just in England. Wales, Scotland and Northern Ireland are going through similar upheavals, which can further tangle up specifiers and designers, especially those working on projects in different regions across the UK.

One way to simplify compliance is to opt for holistic building systems, such as Marley’s complete roofing system. A system approach to roofing for residential projects, ensures that all requirements are considered, delivering a single-source solution that meets all relevant regulations and recommendations as well as any additional design preferences.

The need to reduce carbon emissions and improve efficiency in housing

Humans, and our reliance on fossil fuels, have had a significant impact on the climate and unless we start making meaningful changes today there is the potential for irreversible impacts on our planet. Scientists have now set out a few thresholds that, if crossed, could lead to severe and potentially permanent environmental consequences. These include loss of Arctic Sea ice, disruption of ocean circulation and thawing of permafrost.

The most commonly cited tipping point, however, is the 2°C warming limit set out in the Paris Agreement. That is, global warming needs to be kept to less than 2° above pre-industrial levels. Many experts say we should really be aiming for 1.5°C. If global warming rises above these numbers, we're likely to see more severe weather events – even worse than we're already witnessing.

Residential housing is a significant contributor to the UK’s carbon footprint. According to the Office for National Statistics, households account for 26% of total emissions in the UK. A significant portion of this comes down to the poor thermal efficiency of our existing housing stock.

Research from University College London found that the UK has some of the least efficient homes in Europe, losing heat up to three times faster than houses on the continent. This is bad news for the environment, and it also leads to cold homes, unwell occupants and excess money spent on energy bills. These problems are particularly important to consider in social housing situations, where the housing stock is often older and less efficient and where vulnerable residents are more likely to suffer the ill effects of fuel poverty.

By upgrading the existing housing stock and ensuring that all new homes meet – or, preferably, exceed – the legislative requirements, we can help to avoid climate catastrophe while also ensuring that people live in comfortable homes that they can afford to keep warm in the winter.

The role of Part L and the FHS in low-carbon housing

Part L and the Future Homes Standard, which will come into effect in 2025, are two critical pieces of legislation relating to minimising the impact of housing on climate change. Both apply to new builds (and relevant retrofits) in England, although similar requirements are either in the works or already applicable in the devolved nations.

Approved Document L – Conservation of Fuel and Power – was updated in 2021 and came into full effect in 2022. It takes a fabric-first approach to a building's thermal performance. It requires that all new homes produce at least 31% fewer carbon emissions, emphasising air tightness, insulation and eliminating thermal bridging. It requires an energy-efficient building envelope and specifies U-value requirements for floors, walls, windows and the roof. The updated Part L was seen by many as a precursor to the more rigorous Future Homes Standard.

The FHS is currently out for consultation and was due to complete on the 6th March 2024, but has had the deadline extended to 27th March 2024 which was predominately down to an issue with the Home Energy Model Software giving incorrect results. It is still expected to come into force in 2025. It will require all new homes to be highly energy efficient, using low-carbon heating and producing 75–80% fewer emissions than current requirements. Existing homes undergoing relevant refurbishments or extension projects will also need to comply.

The FHS consultations has proposed two notional dwellings, based on the same fabric standards as Part L 2021 but it will no longer be possible to meet the standard with gas heating, so all new homes built after the regulations come into force will be electrically heated or use a heat network. The new homes will be classed as ‘zero carbon-ready', meaning that they will be zero carbon once the electricity grid has been decarbonised. Option 1 includes a heat pump along with solar PV, enhanced air-tightness compared to current regulations, decentralised mechanical extract ventilation (dMEV) and a waste-water heat recovery (WWHR) system. Option 2 removes the solar PV, heat recovery and ventilation and relaxes the air-tightness requirement and seems to go against one of the Governments desired policy outcomes to “Protect occupants against high energy bills”, as although heat pumps are extremely efficient and low carbon they can be very costly to run, especially if not used in conjunction with solar PV.

Other relevant standards and regulations that must also be considered in relation to building energy-efficient, warm and comfortable new dwellings include Approved Document O, which aims to mitigate overheating in new residential buildings; Approved Document F, which covers ventilation; and BS 5250: management of moisture in buildings. There’s also the new Approved Document S, which requires electric vehicle (EV) charging points in various new-build settings – combining EV charging with rooftop solar panels can provide a low-cost and low-carbon solution for transportation.

The benefits of roof system specification

A whole-roof system, such as Marley's complete roofing system, brings together everything needed to create a compliant roof covering from the battens up, including underlays, roof tiles, solar panels, ventilation and fire protection.

Our comprehensive roof system streamlines specification, ensures product compatibility, supports compliance with all existing regulations and can help future-proof homes in relation to upcoming carbon-reduction requirements.

A system approach also helps to ensure that the as-designed specification is maintained throughout the life of the project. It’s delivered as a single solution, with all necessary components, mitigating the performance gap, simplifying site logistics and streamlining installation. The result is an energy-efficient, reliable and attractive roof.

In addition, a system approach provides more traceability within the supply chain, making it easier to evaluate the sustainability of materials and providing reassurance that products will provide adequate performance.

For more information, visit our dedicated webpage on Marley’s complete roof system. You can also contact us for advice and guidance on how roof systems can support a home’s energy efficiency strategy.

Category: Roofing Standards