What does 2026’s extreme summer weather mean for building surveyors?

A summer that changed the conversation

The British relationship with the weather has always been a particular one. It is changeable, unpredictable, and a reliable source of conversation. But summer 2026 was something different. According to provisional data from the Met Office, it was the UK's hottest on record, with an average mean temperature of 16.5°C across June, July, and August.

Five widespread heatwaves. Forty days above 30°C, smashing the previous record of 34. Ten days above 35°C, doubling the previous record set in 1976. The highest temperature of the summer was 38.1°C at Kew Gardens on 13 August – the UK's fifth-hottest day on record. Drought was declared across all of Wales and more than two-thirds of England.

The Met Office attributes this summer's heat to have been made around 130 times more likely by human-induced climate change. The question for those of us working in the built environment is not whether summers like this will recur. It is how frequently they occur and what they mean for the buildings we survey, advise on, and manage.

The building surveying team from our London and South East region got together to work through that question.

Subsidence, heave, roots, and foundations

One of the most significant structural risks associated with prolonged heat and drought is subsidence.

During extended dry periods, surface water that would normally percolate slowly into the subsoil instead runs directly into drainage systems, reducing the moisture available to vegetation at shallow depth. Trees and shrubs respond by extending their root systems deeper in search of moisture, drawing water from subsoil layers that foundations are not typically designed for.

The problem is that most foundations in the existing building stock were designed around the root behaviour of local vegetation in a climate that no longer fully applies. As trees extract moisture from deeper sub-soil layers, differential settlement becomes more likely, and the condition surveys and building surveys we carry out need to reflect this evolving risk.

For new development, the implications reach further. Designing foundations to accommodate greater root depth means more concrete and deeper construction, with direct cost consequences that clients and developers will need to factor into feasibility appraisals. Challenging designers to consider these scenarios at the outset is increasingly part of the building surveyor's role.

Drainage infrastructure under pressure

Summer 2026 brought more than just heat, with cities like Sheffield recording more than a month's worth of rain in a single week in late August. This pattern of prolonged dry periods followed by intense, concentrated rainfall is becoming characteristic of UK summers, and it is exposing the limitations of drainage infrastructure designed for a different climate.

Rainwater goods specified to historical norms manage the majority of rainfall events without difficulty. But more frequent cloud bursts are pushing existing gutters and downpipes beyond their design capacity. When they reach that capacity, water overflows, resulting in penetrating damp, damage to fabric, and the kind of defects that planned preventative maintenance programmes are designed to catch before they become costly.

For surveyors, there is now a genuine question to put to clients at the design and refurbishment stage: what is the cost of upsizing rainwater goods now against the cost of managing water ingress and remedial works later? That is a calculation that the changing pattern of UK rainfall is making more pressing.

Crack identification and building pathology

Understanding how a property is constructed has always been central to sound building pathology. Crack identification is a good example of where climate context is becoming increasingly important. The patterns of cracking we observe in buildings are unlikely to change fundamentally, with the underlying mechanisms of thermal movement, settlement, and structural loading remaining the same. However, the degree to which buildings are being pushed toward the extremes of those mechanisms is increasing.

Buildings designed for a temperate climate are being exposed to temperature ranges, moisture cycles, and ground movement that their specifications did not anticipate. Surveyors need to view defects within the wider context of environmental conditions, considering what the changing climate is likely to do to it over the remaining life of the structure, or during the lease term.

Our insight on regulatory compliance for commercial properties touches on some of the emerging obligations that sit alongside this evolving physical risk.

Thermal stress in curtain walling and cladding systems

Curtain walling and cladding systems are among the building elements most sensitive to extreme heat, and the summer of 2026 will have tested many of them beyond their design parameters.

These systems work within defined tolerances for thermal expansion and contraction. When temperatures reach the extremes recorded this summer, differential movement between glazing units, aluminium framing, and seals can exceed those tolerances, leading to seal failure, gasket degradation, and in more severe cases, glass cracking. Once seals fail, water ingress pathways open up that would not be present under normal conditions, and the damage can be difficult to trace back to its origin without a thorough investigation.

Modern curtain walling is particularly susceptible because the tolerances built into its design are tighter than in older systems. Surveyors inspecting commercial buildings with significant glazed facades following a summer like this one should be looking specifically for evidence of seal deterioration and movement at junctions, not just the more visible signs of water penetration that may follow later. Our insight on how regular property inspections protect your investment sets out why this kind of proactive assessment matters.

Masonry decay, timber deterioration, and the moisture cycling risk

Prolonged dry periods draw soluble salts to the surface of masonry through evaporation, weakening the material before intense rainfall arrives. When water returns rapidly, as it did in late August 2026, it enters already-compromised masonry, accelerating spalling, face erosion, and mortar joint deterioration. Exposed timber faces a parallel risk: drought causes shrinkage and surface checking, and when rainfall follows, the same timber reabsorbs moisture quickly, creating conditions for fungal decay to establish in elements already stressed by drying.

Both materials are further compromised where protective finishes have been degraded by prolonged UV exposure. Where coatings have failed on external joinery, flat roof decking, or exposed structural timbers, moisture enters unprotected material, and decay can establish rapidly. The freeze-thaw cycles that follow in winter add a further layer of risk, as water that has penetrated stressed masonry or timber expands on freezing, widening existing micro-cracks and accelerating surface loss.

Post-summer inspections should assess protective finishes and surface materials carefully, recording whether damage is in its early or advanced stages, and the appropriate remedial response differs significantly between the two.

Mechanical and electrical systems and energy efficiency

The biggest operational impact of extreme heat falls on mechanical, electrical, and plant systems. Systems designed to maintain comfort within historical temperature ranges are being asked to work harder and for longer, and in many buildings, particularly older commercial stock, the design criteria do not accommodate the temperatures we are now routinely seeing.

This creates a direct tension with the energy efficiency agenda. Cooling systems working beyond their design parameters consume more energy. The buildings most exposed to overheating are often those with the poorest fabric performance. Addressing that tension requires a fabric first approach that reduces heat gain through the building envelope before specifying or upgrading mechanical systems.

Our decarbonisation team works alongside our building consultancy colleagues on exactly these questions, and the heat wave building risk insight on our site sets out the broader case for acting now rather than waiting for conditions to worsen further.

The profession's response

The UK construction industry has historically built for a middle-of-the-road climate: warm summers, mild wet winters, and relatively predictable conditions in between. That baseline is shifting faster than the industry has so far responded to. As surveyors, our obligation is to advise clients on the buildings they have now and the conditions those buildings will face in the years ahead.

That means keeping pace with changes in construction technology, reviewing specification assumptions that were set in a different climate context, and challenging designers and developers to consider how their buildings will perform if extreme climate becomes a regular occurrence rather than a record-breaking exception.

The conversation about the weather, it turns out, has never been more professionally relevant.

Speak to our London and South East building consultancy team

Our London and South East team works with commercial property owners, occupiers, and developers across the full range of building surveying and advisory services.

If you want to discuss how climate-related risks are affecting your buildings, or how to plan ahead for a changing environment, we would be glad to help. Please use the form below to arrange a no-obligation consultation.