As part of the UK’s target to achieve net zero greenhouse gas emissions by 2050, the introduction of Future Homes Standard legislation (FHS), announced in 2019, recently came into force on 15 June 2022. New homes built from 2022 must produce 31% less carbon emissions, growing to a 75-80% reduction by 2025. These ambitious, yet mandatory, targets have encouraged industry professionals to discover beneficial methods to achieving such goals.

Achieving these aims has become more urgent following the Sixth Carbon Budget of April 2021, further necessitating greener practices in the public sector. Targeting a 76% decrease in greenhouse gas emissions by 2035 in comparison to 1990 levels, recommendations from the independent Climate Change Committee is set to take the UK more than three-quarters of the way to achieving net zero by 2050.

Architects, surveyors and specifiers are now under pressure to conform to the new regulations by selecting products able to provide small yet significant benefits. Of these, windows stand out as an area where improvements can be made. Indeed, according to findings published by the Energy Saving Trust in March 2022, installing high-performance double glazing to a semi-detached gas-heated property could result in annual savings of up to £175 and 410kg of carbon dioxide. These improvements underline the potential of windows in this arena and demonstrate why industry professionals should pay further consideration to frames used if they are to make necessary gains towards the new FHS uplifts.

Setting Standards

Determined by initial updates to Parts L and F of the FHS building regulations, the former covering energy efficiency through the conservation of fuel and power. Products such as windows and doors installed into new build projects or replacing existing systems must comply with specific U-values. Additionally, Part F provides a range of ventilation requirements to ensure efficiency.

Covering projects for new dwellings and refurbishment work, updated requirements to Part L have resulted in the optimisation of window U-values, an element crucial to denoting thermal resistance of layers constituting building elements. The recently implemented regulations have set a target U-value for windows of 1.2W/m2K, restricting the lowest specification allowable – the limiting U-value for SAP calculation – to 1.6W/m2K.

Concerning doors within new builds, those with a glazed area greater than 60% must similarly achieve a target U-value of 1.2W/m2K, alongside doors below the 60% benchmark at 1.0W/m2K. Furthermore, replacement windows within existing dwellings must attain a Window Energy Rating (WER) of B or higher, with a maximum U-value of 1.4W/m2K. Replacement doors with a glazed area larger than 60% must achieve a WER C, or B for those less than that figure.

These concise requirements have been established over a long period of time, following their initial introduction in the Government’s 2019 Spring Statement, two years ahead of implementation. This significant legislation is set to be discussed further in Spring 2023, whereby technical consultation on the proposed specification of the FHS will once again face scrutiny and debate.

Future-Proofing Materials

In the aim of complying with ambitious targets, local authorities must select sustainable materials capable of maximising overall performance on their projects, while remaining cost-effective.

Of the options available, polymer has risen in popularity due to the pace of innovation around material performance and sustainability since its introduction in the 1980s. The material is crucial to eliminating thermal bridging within new build houses – a major heat loss issue within homes. Alongside this, the production of frame foils that can provide convincing facsimiles to materials such as aluminium and wood has proved vital in heightening the visual appeal of PVCU.

It is also important to note that polymer solutions have already been developed that adhere to FHS uplifts. For example, REHAU’S TOTAL70 window and door system has long exceeded the relevant building regulations, ensuring new-build and refurbishment work of the highest quality. Additionally, the organisation’s GENEO solution is able to achieve U-values needed for future PassivHaus projects.

Ventilation Navigation

The pace of change surrounding the legislation can also be seen in what is mandatory under updated Part F requirements. Specifically, new windows must be supplied with trickle vents unless ventilation is achieved by other means, including Mechanical Ventilation with Heat Recovery systems. It must also be ensured that when replacing windows vents are not smaller than those on the original window, additionally allowing either automatic control or from the building’s occupants. For original frames without trickle vents, these must comply with Minimum Equivalent Air Area requirements (EQA).

The EQA is the minimum amount of air that passes through new vents, also achieving approval under test conditions whereby a minimum of 8,000mm2 is specified for both kitchens and habitable rooms in multiple floor dwellings, and 10,000mm2 in single-storey dwellings. While there is no minimum EQA for utility rooms and sanitary accommodation, bathrooms with or without a toilet must adhere to at least 4,000mm2.

Subsequent guidance outlines three separate ventilation systems within new builds. System 1, recognised as Natural Ventilation, is used in building projects deemed as ‘less airtight’, and allows for use of trickle vents. Defining ‘less airtight’ is determined using design stage calculation that shows air permeability higher than five cubic metres of air surpassing the fan per hour to produce an imposed pressure differential of 50 pascals.

By dividing the resultant figure building’s envelope area in square metres, expressed as 5m3/hm2 at 50Pa, establishes the overall metric. In regard to air tightness tests carried out following the build, this figure must show air permeability higher than 3m3/hm2 at 50Pa. Additionally, consultation should be considered in specific situations when using System 1 whereby minimum EQAs may be subject to change, these can be viewed here.

Mechanical Extraction

System 2 within the guidance specifies for properties using continuous mechanical extract ventilation, and mandates trickle vents with a minimum EQA of 4,000mm2 for each room. Additionally, there should be two more vents than the number of bedrooms in a building.

System 2 uses mechanical extraction, allowing for trickle vents with a minimum EQA of 4,000mm2 for each habitable room. The number of vents in a building should be two more than the number of bedrooms within a building. Regarding System 3, the new guidance allows for mechanical ventilation systems with heat recovery with no provision for background ventilators. The variable, in-depth and highly technical nature of these requirements, alongside those pertaining to Part L, make clear that additional expertise may be required if the local authority sector is to come to grips with the FHS uplifts.

It is with this in mind that REHAU’s commercial technical team is working in partnership with those designing public sector dwellings to support the specification process. To ensure compliancy with new regulations, the team are additionally offering free CPD courses to provide further assistance.

Steve Tonkiss is head of sales – south at REHAU Windows.