We check tomorrow's weather before leaving the house. We compare flood risk before buying a home. We insure against events that may never happen. Planning for the future is second nature for humans.
Yet, when it comes to the buildings where we spend around 90% of our lives in, we have traditionally done the opposite. Until the last decade, buildings in the UK have largely been designed using weather data from the past rather than the climate they will experience over the next 50 years.
This contradiction sits at the heart of one of the built environment’s biggest blind spots: we are designing buildings for the climate of the past, while living through the climate of the future. Recent heatwaves have shown that this gap is no longer theoretical. It is being felt in our homes, workplaces and public spaces.
Why designing for yesterday's climate is no longer enough
To understand why this happens, we need to look at one of the most overlooked inputs in building design: the weather file.
Every building simulation starts with a weather file. These datasets underpin assessments of energy performance, overheating risk and occupant comfort by describing the outdoor climate a building is expected to experience.
In the UK, current building regulations reference the CIBSE weather files released in 2016. These include Test Reference Years (TRYs), representing an average climate based on weather observations from 1984–2013, alongside Design Summer Years (DSY1), representing a projected hotter-than-average summer climate for the 2020s and used for overheating risk assessments.
When our climate was assumed to be relatively stable, this approach made sense. Today, it deserves a second look.
To date, 2026 has been a record-breaking year. More than 150 weather stations recorded their highest maximum temperatures in June, while periods of extreme daytime heat increasingly lingered into the night. Our climate is no longer a fixed baseline. It is a changing system, and our buildings must adapt accordingly.
Then why is it that historical weather files remain the norm for building design?
Climate change continues to be politically contested in some parts of the world. Engineers are also rightly cautious about overdesigning buildings based on uncertain futures, particularly where this could create unnecessary costs and resource demands.
However, framing this as a choice between designing for today or designing for 2080 misses the point.
The question is no longer whether future weather files should be used. Nor is it about finding a single future scenario that every building must comply with.
A risk-based approach to future weather files
The challenge now is to move beyond a one-size-fits-all compliance approach and adopt a risk-based framework for assessing future climate impacts on the built environment. For more than a decade, CIBSE has been at the forefront of developing future weather files that enable engineers to adopt this risk-based approach, providing the climate data needed to assess building performance under a range of future climate scenarios.
The latest set was released in 2025, bridging climate science and engineering practice by translating UK climate projections from the Met Office and IPCC emissions scenarios into weather files that engineers can use. Developed with the University of Exeter and validated by Loughborough University, these datasets enable designers to assess building performance across a range of plausible future climates, from the 2030s to the 2080s, rather than relying solely on historical conditions.
CIBSE's future weather files offer far more than a route to compliance. Their real value lies in enabling scenario testing through a risk-based approach, supporting the design of buildings that are resilient to future climates.
That approach starts by asking better questions. When is the first plant replacement or major refurbishment expected, and how long is the building expected to remain in use? Who will occupy it, and how vulnerable are they to overheating? What level of climate risk is acceptable to the client? Which future climate scenarios best reflect those risks?
The answers should shape the choice of weather files, time horizons, emissions scenarios and probability percentiles used in the assessment. Rather than designing for a single future, we should be testing how buildings perform across a range of plausible futures.
Going one step further, alongside the standard Design Summer Year (DSY1) required for compliance, the DSY2 and DSY3 files allow designers to stress-test buildings against increasingly severe heat events and prolonged periods of extreme temperatures. They provide insight not only into whether a building meets today's expectations, but whether it will remain resilient as the climate continues to warm.
Connecting climate science with resilient building design
Ultimately, it is about designing buildings that remain safe, comfortable and fit for purpose throughout the climate they will actually experience. Because this is not simply a building performance issue. It is a public health issue. It is an equality issue. It is a human issue.
Extreme heat does not affect everyone equally. Older adults face greater risks from heat-related mortality. Pregnant women experience increased health risks during periods of extreme heat, including preterm birth and hypertensive disorders. People living with cardiovascular disease, dementia, diabetes and other chronic illnesses are also disproportionately vulnerable to a warming climate. Using this risk-based approach to holistically test buildings against plausible futures, including those with intense and prolonged heat events, is one practical way we can strengthen our design approach and create spaces that better serve the communities who rely on them.
Future-proofing has never been about predicting the future perfectly. It is about making better decisions with the knowledge we already have.
Ultimately, this is about connection: connecting climate science, policy, engineering practice and the people who use our buildings.
Climate scientists are building our understanding of how the climate may evolve. The Met Office translates that science into UK climate projections. CIBSE translates those projections into tools the built environment can use.
The final connection lies in the hands of engineers.
If we truly want buildings that stand the test of time, we must stop designing only for the climate we remember, and start designing for the climate that future generations will inherit.
To learn more about and access CIBSE’s future-ready weather files for accurate and efficient building performance modelling click HERE
CIBSE Climate Adaptation and Resilience Conference 2026
Join us for CIBSE’s Climate Adaptation and Resilience Conference 2026 on Wednesday, 21 October, exploring practical, evidence-based approaches to building resilience against overheating, flooding, moisture and water-related risks. Hear from experts and explore real-world case studies, climate risk assessment, retrofit solutions and emerging policy requirements to help futureproof buildings and infrastructure for a changing climate. Register HERE