When the heat is on, clay brick comes into its own

With exceptional June temperatures and rare red extreme heat warnings putting overheating firmly on the design agenda, the thermal performance of wall systems deserves closer attention. Clay brick is often valued for its durability, longevity and architectural character but its role in helping buildings stay more stable in hot weather is just as important.

As the UK experiences record-breaking June heat, the question for architects is no longer whether overheating matters, but how best to design for it. Recent extreme heat warnings have highlighted the impact of exceptionally high daytime temperatures, high humidity and tropical nights where temperatures may not fall below 20°C.

That matters because thermal performance cannot be judged on winter heat loss alone. U-values remain important, but they only tell part of the story. In hot weather, buildings are exposed to changing solar gain, fluctuating external temperatures and warm nights that make recovery harder. To understand how a walling system performs in real conditions, designers need to look at its dynamic thermal behaviour, not simply a static measure of heat loss.

For architects and specifiers, the benefit is clear: wall constructions that slow and moderate heat transfer can help improve summer comfort, reduce overheating risk and support lower-energy design strategies. That makes material choice more than a question of appearance or compliance. It becomes part of how a building performs for the people using it.

Clay brick has a valuable role to play here. Alongside its weather resistance, fire performance, acoustic qualities and long-term durability, brick also brings thermal capacity. Heavyweight materials absorb heat and release it more gradually, helping to reduce internal temperature swings and create more stable indoor conditions.

The principle of thermal shielding is particularly relevant, especially where heavyweight materials sit outside the insulation layer. In this position, clay brick can absorb significant amounts of heat as external temperatures rise, before substantial heat flow is driven further into the building. In practical terms, that means an external brick skin can help delay and soften the impact of peak daytime heat.

One of the most useful ways to understand this is through decrement delay.  The time lag between the peak temperature on the outside of a wall and the peak temperature on its inside face. Put simply, it is a measure of how long the wall can hold back heat. Medium and heavyweight walls insulated to current standards can slow heat transfer by around 9 to 12 hours, an optimum range for helping to control overheating.

For designers, that is a meaningful advantage. If peak daytime heat is delayed until later in the evening, it becomes easier to manage through passive means such as ventilation and night cooling. It is a more useful way of thinking about summer thermal performance because it focuses not on a static number, but on how the building actually behaves across the hottest hours of the day.

The evidence behind this is compelling. Research into external walling systems tested under dynamic weather conditions shows how an insulated cavity brick module can perform strongly because of the combination of insulation and thermal shielding. The outer brick skin can make a positive contribution to overall thermal performance, while thermal mass located internally also helps moderate indoor temperature.

That is an important point. It suggests the external leaf is not thermally irrelevant simply because it sits outside the insulation layer. Used intelligently, clay brick can actively support summer comfort as part of a broader fabric-first approach.

The lesson is not that clay brick is a standalone answer to overheating. Good summer performance still depends on a coordinated strategy that includes insulation, shading, ventilation and orientation. But clay brick can make a meaningful contribution within that wider approach,  helping architects balance architectural quality with robust building performance.

As hotter summers become more common, designing for overheating is no longer optional. It is an essential part of creating buildings that remain comfortable, resilient and fit for the future. Clay brick deserves to be part of that conversation — not just for how it looks, but for how it performs.

Read the BDA study into brick skin thermal performance to find out more.

If you are looking to create buildings that work harder in summer as well as winter, wienerberger can help you explore clay brick solutions that support comfort, durability and long-term performance.

Speak to our team to discuss materials, wall build-ups and specification approaches for a hotter future.