3 reasons to design 150mm cavities

The construction industry is always changing. Whether through new regulations, evolving needs, or trends in best practice - specifiers must adapt. One such change is the shift towards building wider cavity walls, which 41% of housebuilders have already adopted. Here are the three most important reasons to start designing wider cavities.

1. Maximum flexibility

Building with wider cavities provides more options. Recent years have shown that the supply of common insulation products can be volatile, with prices rising dramatically or products becoming unavailable. This major logistical headache can be avoided with wider cavities because contractors will have a wide range of insulation products to choose from to enable compliance.

By adopting wider cavities filled with high performance insulation, you can also prepare your buildings for low or zero carbon technologies such as air source heat pumps. Again, flexibility is the key here, as the wider cavity gives occupants the option to adopt these technologies when the time is right.

2. Thermal performance and compliance

Insulation that delivers real performance is essential for meeting increasingly tight regulations. The Building Regulations were updated in 2022 in anticipation of the Future Home Standard, expected in 2025, requiring a 75-80% reduction in carbon emissions compared to homes built under 2013 regulations. Part L (Conservation of fuel and power) now requires all walls to have a maximum U-value of 0.26 W/m²K.

Increasing cavities to 150mm wide reduces thermal transmittance and allows housebuilders to use insulation that’s less prone to air gaps, such as mineral wool, maximising thermal performance.

3. Rising demand for non-combustible, low carbon insulation

The 2017 Grenfell tragedy has heightened awareness of fire safety issues and increased demand for non-combustible insulation. Insurers, local authorities, and customers want assurance that the insulation will not contribute to a fire, regardless of the building’s height or use. Demand is also rising for materials with low embodied carbon – the emissions released over a product’s lifecycle.

Switching to 150mm cavities allows the use of insulation that is non-combustible and low carbon while still meeting thermal performance requirements. DriTherm® Cavity Slab 32, for example, has the best possible Euroclass A1 reaction to fire classification and is made from glass mineral wool, which has the lowest embodied carbon of any mainstream insulation material.

Building for the future

Despite some uncertainty about how regulations will evolve in the next few years, the direction is clear - we should aim to create homes that are comfortable, low-carbon, and affordable to run. Although 150mm cavities are not yet a requirement of the Building Regulations, it is likely they will become necessary within the next five years. Specifiers will play a critical role in this transition and can get ahead of the curve now, building for the future and not just for the present.