Addressing the need to improve the building fabric a ‘fabric first’ approach was at the heart of the Government’s ECO (Energy Company Obligation)[1] scheme to insulate existing homes and reduce carbon emissions. That scheme is now coming to an end and has been replaced by the Warm Homes Plan[2]. The new plan places greater emphasis on high-tech solutions such as solar PV, battery storage and clean heat from non-fossil fuel sources, rather than prioritising improvements to the building fabric itself.
This strategy is being presented as the most effective way to improve energy efficiency and reduce household energy bills. The Warm Homes Plan aligns with the phrase ‘Fabric Fifth’, used by some within the industry to describe this shift away from a fabric first philosophy. It prioritises heat pumps, smart controls, low-cost measures such as draught-proofing, solar PV and battery storage over fabric improvement.
This change in emphasis raises an important question: is abandoning the long-established principle that improving the building fabric is the best way to deliver energy-efficient homes with improved thermal comfort and indoor air quality as well as low running costs really the right course of action?
In this piece, we take a detailed look at the proposals within the Warm Homes Plan alongside the established benefits of adopting a fabric first methodology. We examine both through the lens of the home and its occupants, assessing just how important fabric improvements remain in achieving a successful long-term outcome.
Is addressing the building fabric first a fundamentally good idea for energy efficiency?
The fabric first strategy is founded on sound principles. Improving the thermal performance of the building fabric, including the walls, floor, roof, windows and doors, enhances the overall energy efficiency of a home by:
- Reducing the rate of heat loss through the building envelope by using insulation effectively
- Carefully detailing junctions to minimise thermal bridging and associated heat loss
- Reducing gaps in the building fabric to improve airtightness and prevent draughts and unwanted heat leakage
Whenever the fabric is enhanced, it is important that an adequate ventilation strategy is also in place to remove stale air and moisture vapour to maintain good indoor air quality.
The fabric first measures reduce the demand placed on the heating system. As a result, it has to work less and consume less energy, and this is the case whether that energy is derived from fossil fuels or low-carbon sources.
This final point is particularly important when considering the Warm Homes Plan’s focus on clean heat through the use of heat pumps. If the thermal performance of an existing building is poor, there is a risk that a heat pump with a higher-than-necessary capacity will be specified to compensate for the increased heat demand, adding unnecessary upfront capital cost.
Furthermore, if the homeowner later improves the building fabric, for example, by installing external wall insulation, the heat pump may become oversized for the reduced heating load. This can lead to frequent on-off operation, known as cycling, which reduces system efficiency, increases running costs and may contribute to additional wear and tear over time.
What part does building fabric play in the Warm Homes Plan?
To get a better understanding of the role that the building fabric will play in the Warm Homes Plan, we will have a look at how it is referenced within the scope of the scheme and its goals.
Scope and goals of the Warm Homes plan
The Warm Homes plan is a £15bn government scheme designed to:
1.Cut bills
- By helping to upgrade five million homes by 2030 through direct support for low-income families.
- Making grants and low and zero-interest finance available for homeowners to cover the upfront cost of solar or battery installation.
- New-build homes will enjoy the benefits of solar panels, high levels of energy efficiency and clean heat as standard.
- Private tenants will save money with a better insulated, warmer home without the damp and mould issues that so many face today.
From a building fabric perspective, the plan seems to acknowledge the fact that new-build homes deliver a high level of energy efficiency and better insulated properties, which can help reduce issues like damp and mould that can affect health. If we follow this argument, which is a perfectly reasonable one, then it seems to support the case that fabric should remain the first choice to help deliver homes that provide a warm and healthy indoor environment.
2. Tackle fuel poverty
- Help up to one million households out of fuel poverty by 2030 through public investment.
- Introduce new minimum energy efficiency standards for private and social landlords.
Again, energy efficiency gets a mention. It is very hard to achieve without paying attention to the thermal performance of the building fabric and this is supported in the Warm Homes Plan document, where it states that, “Fabric insulation measures, when installed with appropriate ventilation, remain a cornerstone of energy efficiency”[3].
However, looking at the diagram shown on pages 36 and 37 of the Warm Homes Plan,[4] of a high-tech home of the future the only insulation shown is within the roof.
Due to issues with the quality of solid wall insulation in the ECO scheme, there appears to be a reluctance to continue to support this under the Warm Homes Plan and cavity wall insulation barely gets a mention in the document.
This seems strange as according to the Energy Saving Trust around 33% of heat can be lost through the walls of uninsulated homes[5]. If this part of the fabric is neglected that would appear to be a missed opportunity to improve the energy efficiency and lower the energy bills of the occupants of high-tech homes.
3. Creating jobs
Create 180,000 additional high-quality, well-paid, future-proofed jobs in energy efficiency and clean heating by 2030. It will unlock £38 billion in total investment across the Parliament.
4. Deliver energy security
Protect households from volatile international fossil fuel markets by accelerating the shift to clean, homegrown energy. Deliver through solar panels, battery storage and low-carbon heating, supported by more affordable and flexible electricity.
On this point, energy security could surely only be enhanced by the addition of a thermally efficient fabric as even less energy would be required by homes, freeing up energy to be used elsewhere by the grid.
What are the challenges faced when applying the fabric first approach to existing buildings?
Given that the Warm Homes Plan signals a shift away from treating the fabric as a priority, we will look at the challenges that a fabric first strategy can bring.
The easiest way to get the best results from a fabric first approach is to apply them to a new build property. All elements can be designed from scratch, built and detailed in the correct sequence and appropriate post construction testing is carried out to check that airtightness, via an air permeability test required by the building regulations, achieves the desired value. It is even possible to check the thermal performance of the fabric via HTC (Heat Transfer Coefficient) testing, although this is currently not a regulatory requirement.
The warm homes plan, like ECO before it, is aimed at existing buildings. Existing homes can present challenges when it comes to upgrading the thermal performance of the building fabric:
- It can be difficult to know exactly what has been built with regards to the composition and construction of an existing home.
- Houses may have been subject to home improvement such as loft conversions or extensions that can change the thermal dynamics and ventilation of the original home design.
- The quality of the work can be variable, and a record of plans and materials used may not be available.
- Measures such as thermal bridging can be harder to address as access may be limited and the exact existing design of existing junction details may be unclear.
With this in mind, it is important to carry out a thorough survey of an existing home in order to be able to evaluate and plan the most appropriate energy efficiency measures taking a whole-house approach. This has been addressed by using a Publicly Available Standard (PAS) known as PAS 2035[6].
Why is PAS 2035 with its fabric first approach used as a standard for retrofit under government schemes?
Due to the complexity of existing buildings carrying out retrofit work on an existing property must be carefully planned and executed. This is why a PAS 2035 was developed.
PAS 2035 details the best way to conduct a retrofit designed to improve energy performance from start to finish. It considers the dwelling as a whole and promotes a fabric first approach. It must be followed by installers when carrying out work under the previous ECO scheme and is likely to also be required under the warm homes plan.
PAS 2035 includes the requirements to carry out a thorough survey of the existing property. This allows the creation of a risk assessment to determine the project's complexity and decide upon the design and installation of the most appropriate energy efficiency measures. These decisions are based on first considering the fabric improvements coupled with any adjustments required to the ventilation strategy.
By addressing the property in this way, the enhanced thermal efficiency of the building fabric reduces the heating demands on any subsequent high-tech additions such as heat pumps. This means that heat pumps can be correctly sized and run in an environment that will help maximise their efficiency and help to reduce energy bills accordingly.
What benefits can a fabric first bring that a technology-led approach cannot?
Upgrading the fabric first can:
- Increase homeowner’s thermal comfort by reducing draughts.
- Reduce the chances of condensation forming that can lead to mould growth.
- Help to limit the effects of overheating by use of insulation materials such as wood fibre boards.
A technology led approach where PV, batteries and a heat pump is installed will give homeowners the benefits of access to cheap electricity and help to reduce carbon emissions. It may not be able to match the benefits that addressing the fabric first can bring.
As with any retrofit project, and in the spirit of PAS 2035, each home should be assessed on its merits. Some will benefit from a focus on fabric first, others may be better positioned to look at installing technologies such as PV, batteries and heat pumps.
It is clear that both approaches bring different benefits to a homeowner and together they can work in harmony to deliver high-tech homes that support thermal comfort, low energy use and lower energy bills for the occupants. It remains to be seen if the Warm Homes Plan signals a major shift away from the fabric first approach and given the benefits that a well-insulated fabric can bring that would run the risk of missed opportunities to optimise the performance of our high-tech homes.
How does insulating the building fabric benefit the occupants of high-tech homes?
There are a number of ways in which insulation can benefit the occupants of high-tech homes where solar PV and heat pumps have been installed:
Insulation helps to enhance the thermal efficiency of the building fabric
Insulating the fabric of the building can enhance the thermal efficiency of the home. This benefits the occupants as less heat is required to maintain the desired temperature and any new heating system can be appropriately sized to match the reduced heat demand. Less heat translates to lower energy use and lower fuel bills for the occupants.
Insulation limits the chances that surface condensation will form
A well-insulated fabric reduces the likelihood that cold spots will be present on the interior surfaces of the home where condensation can form. This is important as mould growth in these damp areas can be harmful to health.
Insulation can increase airtightness
Insulating walls, floors and roofs can help to reduce unwanted draughts by covering any gaps in the fabric of the home. As well as increasing heat loss and reducing energy efficiency, cold draughts diminish the thermal comfort of the occupants.
Insulation can help to mitigate overheating
Certain types of insulation, such as wood fibre boards, can help to mitigate the effects of overheating. Wood fibre insulation combines high density, high heat storage capacity, and low thermal conductivity to significantly help reduce the risk of summer overheating. These properties enable the insulation to absorb and retain heat during the day, slowing its transfer into internal spaces.
This creates a time delay, so peak solar heat does not immediately affect indoor temperatures. The insulation helps to bring thermal comfort to the residents of high-tech homes and reduces the reliance on energy consuming systems like air conditioning.
Diffusion open insulation can assist with control of moisture
Whenever the fabric of a building is insulated, it has the potential to affect the existing system of moisture management within the property. This is a factor that can be of particular interest when insulating some older and heritage solid wall properties as the walls are constructed of materials that allow the walls to breathe. In such cases diffusion open external or internal solid wall insulation may be preferred as it most closely matches the existing behaviour of the building fabric.
Where can I find out more information about wood fibre insulation solutions that can help enhance the energy efficiency of high-tech homes?
STEICO has a comprehensive range of products suitable for use in walls, floors and roofs in new and existing buildings. These include rigid wood fibre insulation boards and flexible wood fibre batts as well as a range of sarking, sheathing and render boards. They are all made from at least 80% natural wood sourced from PEFC* certified forestry and are manufactured to EN standards or have European Technical Approvals.
STEICO insulation boards and batts that are characterised by a higher raw density (volume weight) than many conventional insulating materials. This means that they can offer much greater resistance to heat radiation due to their higher heat storage capacity. The heat of the day is buffered in the insulation material until the cooler evening hours and can help mitigate the effects of overheating.
STEICO wood fibre insulation is also diffusion open, and this can help to provide a solution for specifiers when looking for solutions that can complement the existing moisture profile of properties with a breathable building fabric design.
To discuss how STEICO products can support your building fabric needs, get in touch with our expert team who will be happy to help.