Calculators · Consulting
Overheating quick-check
Part O & CIBSE TM59 · screening
A fast read on a room’s overheating risk using the drivers Part O and TM59 actually weigh, glazing, orientation, shading and ventilation, so you catch the problem rooms while the design can still change cheaply.
The room
The worst-case habitable room is the one to test.
A screening heuristic, not a compliance check. Part O compliance and TM59’s criteria are decided by dynamic thermal simulation against real weather data, which this does not run.
What it weighs
- Glazing ratio, glazing as a share of floor area. The single biggest driver of solar gain.
- Orientation, west and large unshaded south glazing carry the most afternoon gain.
- Shading, external shading cuts gain before it enters; internal blinds help less.
- Ventilation, cross-ventilation and secure night purge remove heat; single-sided struggles.
- Openable area, Part O sets a minimum free area for purge.
Why trust it: it mirrors the drivers in Part O’s simplified method and CIBSE TM59. When it flags risk we run the full dynamic model; every assessment is reviewed by one of our 7 accredited Passivhaus certifiers.
Take it further
Flagged a risk? Model it before it’s built.
We run dynamic simulation (IES/DSM) against TM59 and Part O, so you fix overheating on screen, not with retrofit blinds after handover. Send us the rooms that scored amber or red.