As energy regulations tighten, Matthew Prowse, Specification and Housing Director at Knauf Insulation, discusses specifying insulation to help meet the needs of today and tomorrow.

The last couple of years have seen a significant uplift in regulations around energy efficiency, and the housebuilding sector now needs to deliver homes to higher standards than ever before. Updates to Part L (Conservation of fuel and power) of the Building Regulations for England came into force this June, introducing tighter limiting U-values and a 31 per cent reduction in operational CO2 for new homes. But the industry won’t have long to adapt; in just two more years the Future Homes Standard will arrive, bringing with it a 75 per cent reduction in CO2. So, as energy efficiency continues to climb the agenda for government and house builders, how can you optimise your insulation specification for both the short and longer term?

Prioritise credentials
Lambda, U-values, and R-values have always been key points of comparison when choosing insulation and that’s unlikely to change any time soon. In fact, the recent updates to Part L tightened the limiting U-values for fabric elements in new builds, as a step towards more energy-efficient design. While this is useful guidance, it’s important to remember that each home must comply as a whole, so matching the limiting U-values won’t necessarily result in overall compliance.

Technical credentials are important as they’re a good indicator of a product’s potential thermal performance and therefore its ability to prevent energy waste. But ‘potential’ will only go so far. When specifying insulation, you need to consider how that translates into as-built results.

Prioritise results
Measures like U-values are only meaningful if the product performs as designed. And, under real-world conditions, some products are simply easier to install correctly than others. For example, unless the inside of a wall cavity is completely uniform and flat – which is rare – rigid board insulation won’t sit flush against it. This can result in unintended air gaps, which compromise performance. Boards also need to be taped together with precision, leaving plenty of opportunity for human error.

By contrast, mineral wool insulation like Knauf Insulation’s DriTherm Cavity Slabs, have a flexible structure that adapts to fully fill the cavity. This makes the installation process easier to ‘get right’, and where two slabs meet, they even ‘knit’ together, further minimising air gaps and maximising performance.

When the as-built performance of insulation doesn’t match up to its design, it has a damaging effect on the home’s overall energy efficiency. More energy is wasted through the building envelope and if low-carbon heat sources are being used, they struggle to heat the space effectively. As energy efficiency requirements continue to tighten, it’s essential to prioritise products which deliver on their theoretical performance.

Prioritise comfort
Energy efficiency is often associated with heating homes in winter but it’s critical all year round and that will only become more apparent in years to come. Our climate is changing and as temperatures rise, it will become increasingly important to keep homes cool during the summer months.

This will require a holistic approach to design, considering everything from building orientation to shading, glazing, and ventilation. Insulation will play a crucial role by preserving the internal environment that allows these elements to work effectively. Cooling systems, such as air conditioning, will rely on a well-insulated building envelope to perform efficiently, in the same way as heating systems do during the winter.

Again, this will mean choosing insulation that performs as designed, and mineral wool is particularly well suited to this, because unlike some other insulants, it doesn’t expand and contract with temperature fluctuations.

Prioritise flexibility
When considering different insulation options, it’s also worth giving some thought to the width of your wall cavities. Although it is possible to meet Part L requirements using 100mm cavities, increasing to 150mm gives you more flexibility and the freedom to choose the best insulation solution for your design. When energy regulations shift again in 2025, most homes will likely be built with a wider cavity anyway. By making the change now, you’ll get ahead of the curve and futureproof any larger developments in design today.

Maximising the energy efficiency of your designs means prioritising products like mineral wool insulation, which offer good thermal credentials and are easier to install correctly. Products like these will support compliance with today’s requirements and put you in a good position to meet those which lie ahead.

Contact Details
For free resources on Part L and the wider housebuilding sector, visit Knauf Insulation’s Housebuilders Hub.