What the Approved Document L changes mean for domestic builders

What the Approved Document L changes mean for domestic builders

Wide-reaching changes to Approved Document L come into force this June, but what do they mean for domestic builders? Matthew Neary, Product Manager – Glass Mineral Wool at Knauf Insulation explains how to achieve compliance.

What’s changing?
Approved Document L: Conservation of Fuel and Power sets out new minimum standards for the thermal performance of buildings in England. It will make properties significantly more energy efficient and will affect both new builds and extensions.

As well as improving thermal efficiency, it seeks to close the gap between as-specified and as-built performance. This means builders will need a better understanding of how products perform and how installing them correctly can affect product and building performance.

The new standards come into force on 15th June 2022. However, where a building notice or an initial notice has been given or full plans deposited with a local authority before 15th June 2022, it can be built to the previous standards providing work on that particular building has started before the 15th June 2023. All this means builders must get to grips with the changes fast.

But don’t panic. Whatever your project, there are cost-effective ways to comply with Part L using trusted Mineral Wool insulation solutions.

How does Approved Document L affect extensions?

Under Approved Document L, the ‘limiting U-values’ (minimum thermal performance standards) for every building element have been significantly reduced.

Roofs and floors have a target U-value of 0.15W/m2K. This can be easily achieved by increasing the depth of insulation or using a product with a lower lambda value.

For walls, the situation is more complex. The limiting U-value is now 0.18W/m2K – a significant 0.10W/m2K reduction compared to the previous limit of 0.28W/m2K. To achieve compliance, wider cavities will be needed when using either a full-fill non-combustible Mineral Wool insulation solution, or a partial-fill rigid foam solution with an associated 50mm clear cavity. This shouldn’t be a cause for concern, because widening the cavity on an average 20m2 extension, represents less than 0.6m2 of floorspace.

When deciding on the best insulation solution, remember that focusing solely on thermal performance means that you may inadvertently compromise on other factors. The best and most affordable solution is to use non-combustible Mineral Wool insulation. 

Why use Mineral Wool over other insulants?

One of the most compelling reasons for using Mineral Wool insulation is to minimise the risk of fire. It is non-combustible with the best possible Euroclass A1 or A2-s1,d0 reaction to fire classification, so it will not add to the development or spread of fire should it occur.

Building Regulations already ban the use of combustible insulation in the external walls of certain types of buildings over 18m in England and Wales (11m in Scotland). But there is increasing pressure to use non-combustible materials regardless of building height. This is demonstrated by the publication of the new Homes for Londoners standards, which bans the use of combustible materials in the external walls of all homes regardless of height.

Acoustic performance must also be considered for those applications with low mass such as rainscreen façade systems or timber frame constructions. Unlike other insulants, Mineral Wool is highly sound absorbent so will help to reduce noise.

Builders need to consider the sustainability of the products themselves. Reducing operational carbon (the greenhouse gas emissions from energy used in a building) alone won’t meet the Government’s net zero targets. It also depends on the quality of the building fabric. This means regulations governing embodied carbon (the greenhouse gas emissions generated through the construction of a building and the manufacture of the products used in it) are inevitable. So, products that are lower in embodied carbon should be used.

Knauf Insulation’s Glass Mineral Wool is a good choice when it comes to embodied carbon. Its products contain up to 80% recycled content and are manufactured with ECOSE Technology, its unique bio-based binder, which is 70 per cent less energy-intensive to manufacture than traditional binders. Products can also be compressed so there’s more insulation per pack or pallet, and per truck. This means less packaging used, fewer trucks on the road and less transport-related carbon emissions.

The final factor to consider is how build and install quality can affect product and building performance. This is because alongside the improvements in thermal efficiency there will be closer scrutiny of real-world performance. So, builders need to use the right products and install them correctly to prevent unintended air gaps that reduce thermal, fire safety and acoustic performance.

Mineral Wool is easier to install correctly than other insulants. It adapts to slight imperfections in the substrate and butts together eliminating gaps. By contrast, combustible rigid board insulation such as PIR can be difficult to install correctly. In cavity applications, misaligned masonry or mortar snots can cause breaks in contact between the substrate and the insulation. In timber applications, boards must be cut to the exact profile of the timber. Even if achieved, timber can bow creating gaps over time. Builders must also tape joints and install separate fire barriers in certain applications, which increases installation time, complexity and costs.

One thing that’s certain is that your build must achieve the standards set out in Approved Document L, but how you do it is up to you. The most important thing is there’s a tried, tested, and affordable solution that will help you achieve compliance – non-combustible Mineral Wool insulation.

For further information on the range of solutions from Knauf Insulation visit www.knaufinsulation.co.uk

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