Unlocking the true energy-saving potential of a cavity wall

By Knauf Insulation
April 14, 2022

Making buildings more sustainable is a key priority for South Africa’s legislators. It is therefore essential that the country’s builders and contractors are aware of the implications of the Part XA update to SANS-10400, which focuses on energy use in properties.

The update sets the required thermal performance for each construction element of new buildings and extensions designed for human occupancy. Thermal performance is defined by an R-value, which measures how a material or build-up resists heat transfer.

The required R-value will depend on how the building will be used and in which of the country’s seven zones it is located. In zones 1, 2, 4, 6 and 7, a minimum cavity of 50mm will be mandatory for concrete and brick external masonry walls.

What is a cavity wall?

A cavity wall is formed of two masonry walls, known as skins or leaves, positioned parallel to each other with a small gap (cavity) in the centre. The cavity must be of a consistent depth across the entire width and height of the wall.

Adding a cavity prevents condensation from forming within the building and helps to reduce noise while improving thermal performance, and therefore reducing energy consumption.

However, adding a cavity wall should be just the first step towards better energy efficiency during the construction process. To really maximise energy efficiency, insulation should be added to the cavity during construction. It is important that excess mortar – sometimes known as mortar snots – are removed from the inside of the cavity for it to work efficiently

If a cavity improves energy efficiency on its own, why add insulation?

Research by the Clay Brick Association and the University of Pretoria found that energy consumption was reduced by 30% through the addition of a cavity. Installing insulation reduced energy consumption by 70%.

This is because insulation material has low thermal conductivity which makes it the most efficient way to add thermal resistance to a build-up. As a result, insulation helps to regulate indoor temperature by reducing heat loss or gain through the external walls and roof.

Why use mineral wool insulation in a cavity wall?

When insulating within a cavity you need to consider the fire performance of your products, most Mineral Wool insulation is non-combustible meaning that it is the superior option compared to other insulant types.

DriTherm® Masonry Cavity Slabs have a Euroclass A1 reaction to fire classification and give specifiers added assurance thanks to BBA (British Board of Agrément) certification. DriTherm® Masonry Cavity Slabs are also specifically designed for use in cavities as they are manufactured using a water repellent additive to prevent moisture ingress across the cavity.

All of our Glass Mineral Wool products and the majority of our Rock Mineral Wool products are manufactured using ECOSE® Technology, our unique bio-based binder that is used to bind insulation strands together.

ECOSE® Technology contains no added formaldehyde or phenol. It is made from natural raw materials that are rapidly renewable and is 70% less energy-intensive to manufacture than traditional binders, so it is more environmentally-friendly.

Products made with ECOSE® Technology are pleasant to touch and easy to handle. They generate low levels of dust and VOCs and have been awarded the Eurofins Gold Certificate for Indoor Air Comfort.

For builders and contractors, SANS-10400-XA provides an opportunity to create buildings fit for the future. Adding insulation to a cavity wall will take little time and investment but will pay dividends. After all, property buyers or renters will be attracted by the promise of a comfortable indoor environment that is quieter, needs less cooling and heating, uses less energy, and so, costs less to run.