Future-Proofing Buildings: IES & CIBSE 2025 Weather Data

With rising temperatures and more frequent heatwaves, overheating and cooling energy demand are growing challenges in UK building design. The new CIBSE 2025 Weather Data release offers updated and future-focused datasets that reflect the realities of our changing climate.

At IES, we’re supporting this critical shift. Enabling users to easily access and apply the new files within the Virtual Environment (IESVE) drives designs that are compliant, resilient, and climate-ready. By leveraging these datasets, designers can future-proof their projects, reduce operational risks, and enhance energy efficiency.

From Historical Norms to Future Risks

The CIBSE 2025 dataset introduces:

An updated baseline (1994–2023) reflecting recent UK weather trends.
Projections for the 2030s, 2050s, and 2080s using RCP2.6, RCP4.5, and RCP8.5 emissions pathways.
Expansion to 28 UK climate zones for more regional accuracy.
Improved solar data to enhance shading, glazing, and passive design modelling.

Crucially, these updates help designers better anticipate increased cooling demand and overheating risks, which older datasets often fail to capture, especially in light of the revised TM59 guidance. Additionally, having access to more granular and accurate data allows for better compliance with future regulations and optimises building performance under extreme weather conditions.

What IESVE Users Can Do

The new weather files are available for purchase by contacting sales@IESVE.com to speak with your account manager regarding options. This ensures seamless access and integration for IESVE users.

Benchmarking What Matters

When we discuss benchmarking, we’re referring to comparing building performance across multiple future scenarios, zones, or datasets, for:

Energy demand (especially cooling)
Thermal comfort
Passive strategy effectiveness
Resilience under extreme conditions

This goes beyond minimum compliance. It helps you inform client decisions, shape planning applications, and align with long-term sustainability goals.

Should you already be using the 2025 dataset?

Despite the current Part L2 compliance path still using the older 2016 weather files, CIBSE are encouraging design teams to transition to the 2025 dataset now:

It reflects more recent climate baselines (1994–2023) and future projections.
It better aligns with TM59 and future climate resilience strategies.
It helps build robust energy and overheating simulations today, even ahead of regulatory change.

Best Practice Recommendations

Once you’ve obtained the 2025 files, we recommend:

Use the 2030s TRY (RCP8.5, 50th percentile) as a new design benchmark.
Run DSY1, DSY2, and DSY3 simulations for 2050s/2080s to assess overheating under various heat stress scenarios.
Match your weather file to the correct climate zone using postcode lookup to ensure location-specific accuracy.
Compare results between 2016 and 2025 datasets to quantify changes in risk.
Document assumptions and outcomes clearly for planning and client reporting.

Need Expert Support?

IES offers more than just software - our Consultancy Team of Experts is here to support:

TM59-compliant overheating assessments using future climate data
Passive and hybrid cooling strategy development
Energy performance evaluations under climate stress
Client and policy reporting aligned with net-zero goals

Stay Tuned

We’ll continue to release blogs, tutorials, and webinars to help you adopt these changes confidently. Follow IES channels to stay up to date as we share more practical guidance and best practices.

The CIBSE 2025 datasets represent a step change in how we model climate resilience. By making them available by contacting sales@IESVE.com and fully integrating them into IESVE workflows, we’re helping you design buildings that not only meet today's standards, but withstand tomorrow’s climate realities.