TM59:2026 ,What Has Actually Changed?
from MEP today Hosted by mohamad tabatabaee
CIBSE has published TM59:2026, almost nine years after the original overheating methodology was introduced. But what has actually changed for designers and building-performance modellers? In this episode of MEP Today, I compare TM59:2017 with the new 2026 edition and look at the changes that can directly affect an overheating model, including the revised bedroom criterion, window-opening controls, ceiling-fan allowances, mechanically ventilated spaces, communal areas and internal-gain profiles. We also look at the new passive-first, three-stage modelling approach and an important practical question around ceiling fans: when TM59 refers to an air speed of 0.6 m/s, how should that performance be demonstrated in the occupied zone? Not everything has changed and understanding what remains the same is just as important as understanding what is new.
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