Model the real constraints
Orientation, glazing, exposed thermal mass, occupancy, gains, shading, ventilation and weather data all matter. We also account for relevant restrictions on window use rather than assuming unlimited purge ventilation.
Dynamic thermal modelling
TM59 overheating modelling
Room-level thermal modelling to understand residential overheating risk and test practical design responses.
When you need this work
TM59 modelling looks beyond a single peak temperature. It simulates the building, weather, occupancy and ventilation strategy over time to test defined overheating criteria.
We develop a model proportionate to the project and agree the purpose before work starts. That may be planning support, a client performance requirement, design development or part of a wider overheating strategy. TM59 and Part O are not interchangeable: one is an assessment methodology and the other is an England Building Regulations requirement. A project may need one, the other or coordinated evidence for both.
CIBSE published TM59:2026 in July 2026 and recommends it for current industry best practice. Approved Document O currently still requires TM59:2017 and the 2016 CIBSE weather files for its dynamic compliance route, with additional Part O constraints. Planning policy or a client brief may set another requirement, so every scope and report should name the controlling edition, weather data, criteria and purpose.
What we check
Diagnose before prescribing
Results identify the rooms, periods and conditions that drive risk. This helps distinguish a targeted glazing or shading change from a broader ventilation or façade problem.
Test a clear hierarchy
We assess passive measures first where practical, then consider mechanical strategies within the agreed brief. Every option is recorded so the team can see why it was tested.
Common coordination issue
A planning brief, client comfort target and Part O submission may specify different editions, weather files or criteria. Record the purpose of each run so a result is never used to answer a different requirement.
What you receive
Dynamic model report
Method, inputs, assumptions, results and compliance conclusion for the agreed criteria.
Room-level findings
Identification of the critical spaces and the conditions causing risk.
Option testing
Results for agreed design changes, with requirements that need to pass into drawings and specifications.
Getting started
What we need
Architectural model information
Plans, elevations, sections, room uses, orientation, glazing and shading details.
Building performance
Fabric build-ups, air permeability, ventilation strategy, internal gains and relevant controls.
External constraints
Planning or client criteria, acoustic and air-quality evidence, security restrictions and agreed weather files.
Before commissioning
Is TM59 required on every home?
No. The need depends on the planning policy, client brief, building type and regulatory route.
Can modelling prove that any design is acceptable?
No. The model tests defined inputs against defined criteria. A difficult result may require a real design change.
When is the best time to model?
When massing, façade and ventilation choices can still change, with updates as the design becomes more detailed.
Sources and further reading
Use the edition, jurisdiction and assessment route that apply to the project. Publication of newer guidance does not automatically change an existing project’s requirements.
Define the overheating question first
Send the design stage, location and reason for the assessment. We will confirm the suitable modelling scope and required inputs.