Use this comparison to prepare a scope for our TM59 and TM52 assessment service. The distinctions follow CIBSE TM52 and CIBSE TM59; neither title should replace a written project brief.
| Question | TM52 | TM59 |
|---|---|---|
| What does it address? | Thermal comfort and avoiding overheating through an adaptive assessment framework. | Overheating risk in dwellings through a residential design methodology. |
| Where might it be specified? | A non-domestic thermal-comfort brief, such as a naturally ventilated office proposal. | A residential overheating brief, with any regulatory modifications stated separately. |
| What use assumptions matter? | The occupied spaces, operating pattern and ventilation approach relevant to the brief. | Residential room uses, occupancy and gains appropriate to the selected methodology. |
| How should results be presented? | Against the applicable TM52 criteria for the assessed spaces, with assumptions visible. | Against the applicable TM59 criteria for the assessed residential rooms, with assumptions visible. |
| Can it replace the other label? | An assessment should not be renamed TM59 without applying the residential methodology. | A residential report should not be offered as a TM52 assessment of an unrelated workplace. |
| What must the scope establish? | The purpose, spaces, operating scenario and reporting criteria. | The dwelling sample, relevant rooms, methodology edition and any Part O provisions. |
Separate a TM52 or TM59 brief from a software request
A request for a thermal model leaves important questions unanswered. Is the project testing comfort for occupants, answering a planning condition or preparing Building Control evidence? Who will read the report, and which design choices are still open? Give the assessor the actual question, not just the name of a modelling package. Different assessment purposes can require different inputs and explanations even where the building geometry is shared.
Prepare a short schedule of spaces and their uses. In a mixed-use building, distinguish the dwellings from shops, workspaces and communal areas. Do not assign a methodology to the whole development because one part dominates the floor area. Ask the assessor to explain the proposed treatment of each part and any spaces excluded from the report.
For planning, the requested evidence depends on the council and the wording of its condition or validation requirements. Planning practice guidance on making an application explains local information requirements. Supply the relevant wording rather than requesting a generic planning-compliant model. Our energy statement template guide explains how supporting evidence fits into a planning submission.
Confirm how TM59 is being used for Part O
Approved Document O sets the residential overheating modelling route and provisions governing its use of TM59. A report for that purpose needs to explain its relationship to the Approved Document, rather than presenting an unqualified comfort-study result. Ask the scope to identify the regulatory basis and how the report will demonstrate the required checks.
The linked CIBSE TM59 publication is the 2026 edition. Publication of an updated methodology should not be treated as proof that every regulatory reference or existing project brief has automatically changed. Establish which edition the commission uses and resolve any difference between the requested assessment and the applicable regulatory guidance before the modeller starts.
If the question is whether a simpler assessment would be suitable, read Part O simplified method. That decision belongs before detailed model construction. Commissioning a model first can leave the client paying for a scope that has not been matched to the approval route.
Make TM52 and TM59 assumptions visible to the design team
Create an input register with a source for each design assumption. Link glazing properties to the specified product, shading to sections or elevations, and opening operation to the window schedule. Where a design item is unresolved, label the assumption and give someone responsibility for confirming it. An unexplained default is difficult to review when results depend on that choice.
Pay particular attention to the operating scenario. An accessible window in a drawing might be restricted in the installed product, or an occupant might be unable to use it as assumed. For Part O work, practical constraints on heat removal are addressed in Approved Document O. Discuss noise, security and other relevant constraints before treating an opening schedule as settled.
When testing mitigation, keep the original scenario and revised options clearly separated. A lower temperature in a revised model is useful only if the drawing package and specification include the measures that produced it. Ask for a comparison explaining the design changes, rather than a collection of result files with unclear relationships.
Request TM52 and TM59 outputs that can be reviewed
Ask for a room schedule, model assumptions, assessment criteria, results and a clear list of relied-upon measures. Identify whether the quote includes design-option testing, responses to reviewer queries and updates after drawing revisions. These are scope questions rather than automatic inclusions. Architects can use our architect support page when coordinating several designers around the same evidence set.
Submit the building-use schedule, current drawings and approval brief to our TM59 and TM52 assessment service. Include any earlier report and explain what changed. That allows the assessor to distinguish a fresh assessment from a review of an existing model, and to identify missing evidence before reporting results.
About our CIBSE TM59 and TM52 Assessments service
For the service itself, see CIBSE TM59 and TM52 Assessments.