The FHS is a keystone of the government’s emissions reductions strategy – and timber frame construction is recognised as a prime route to compliance. The target is for the UK to be a net-zero carbon economy by 2050. Currently construction and buildings in use account for around 25% of the country’s carbon emissions.
The FHS – Cutting housing emissions by 75%
The FHS sets out the way new homes are to be built, heated and ventilated to cut their emissions by at least 75% against previous regulations. It means an industry-wide switch to renewable heating technologies and, in conjunction, improvements in building envelope performance to cut energy wastage. Homes will become “net-zero ready” without further retrofitting as the electricity grid fully decarbonises.
Part L changes are core to the FHS
The new FHS rules come into force in March 2027. From then to March 2028 some projects will be allowed to be delivered under previous regulations depending on the dates plans were submitted and construction commenced. From March 2028 all new projects must comply in full.
At the core of the FHS are major changes in Building Regulations Part L on energy performance. It stipulates that heating and hot water must be delivered by electricity, with low-carbon systems, including heat pumps, communal heat networks and photo-voltaic (PV) panel arrays. Gas boilers will no longer be allowed.
New levels of airtightness required by the FHS
The FHS has tightened the airtightness of a notional dwelling to 4 m³/(h·m²). That compares to typical new-build homes currently achieving 4–6 m³/(h·m²) This step change means airtightness assessors will become an essential part of every new build.
New airtightness rules are accompanied in the FHS by changes to Part F on ventilation which address the type of technology and installer competence. In conjunction, a technical review is being undertaken of Building Regulations Part O, introduced in 2022, to reduce risk of homes overheating.
Build fabric considerations are critical to the FHS and timber frame construction
The Government has decided that home fabric standards should remain ‘broadly aligned’ with those of Part L 2021. However, compliance will rely on good insulation, airtight construction and detailing that minimises heat loss at junctions.
A new Standard Assessment Procedure, SAP 10.3, has been developed to demonstrate compliance. This will be superseded by the Home Energy Model, a new calculation methodology expected to be ready shortly.
Timber frame construction is a valid route to compliance
The FHS puts significant demands for improvement on all construction methods, regardless of building materials. However, the timber-frame and broader timber-based building sector believes it is particularly well placed to meet the standard given timber buildings’ inherent strengths in terms of insulation and airtightness. Moreover, the industry continues to make advances in levels of timber-based housing’s lifetime energy performance. It’s doing this through its construction approaches and introduction of innovative new technologies.
One reason timber frame is seen as having the edge in ensuring FHS compliance is that timber itself is an inherent insulant. This helps regulate internal temperatures, reducing energy consumption for heating and cooling. In addition, it is less prone to thermal bridging compared to other construction materials. It typically has deeper wall cavities too, accommodating more insulation.
Timber frame construction can offer component precision
Precision prefabrication of timber frame components additionally enhance airtightness, especially in offsite construction where whole building assemblies are fabricated in factories. Timber is increasingly widely regarded as the prime material for offsite manufacture given its strength to weight and ease of processing. Many leading UK housebuilders now have their own timber frame factories.
Modern timber frame design is also billed as delivering greater flexibility when it comes to incorporating renewable energy technologies, including PV panels, heat pumps and mechanical ventilation, together with associated ducting and services.
Weather-resistant barriers can perform key roles in timber frame construction
The weather resistant barrier (WRB) is a key component in timber frame construction, helping to achieve required energy performance levels. These prevent water ingress and minimize potential problems with timber movement, mould or decay.
The most widely seen WRB type in the UK is probably the site-fixed polypropylene or polyethylene house wrap. An older technology is building paper, which is asphalt-impregnated kraft paper. More modern solutions include self-adhered peel and stick membrane solutions and fluid-applied products.
These all support building airtightness and perform an effective protective function. In addition, bar building paper, the systems are vapour-permeable allowing any moisture in the building envelope to escape.
Thermally fused integrated weather resistant barriers
Thermally fused integrated WRBs are applied in factories under heat and pressure. This means consistently uniform coverage, leaving no gaps for water ingress. Processed panels using solutions such as Arctek® Dryshell™ are delivered to site ready-protected or can be incorporated into timber frame assemblies in offsite factories.
Deskilling the timber frame weather protection process, WRB’s help deliver quality, high performance, low carbon timber frame homes that the FHS requires UK construction to build in the future.