CIBSE TM49
Overheating Analysis

For Greater London Authority Developments

CIBSE Technical Memorandum 49

Overheating Analysis for Greater London Authority

Overheating risk analysis for buildings in the Greater London Authority follows CIBSE TM52 methodology but uses the weather scenarios specified in CIBSE TM49: Design Summer Years for London.

Weather Data

CIBSE TM49 Weather Scenarios

TM49 defines three Design Summer Year (DSY) scenarios for London, each representing a distinct type of summer heat event:

DSY1

Design Summer Year — Primary Scenario

2020s, high emissions, 50th percentile scenario. The primary weather file used for all TM49 assessments.

DSY2 — 2003

Intense Single Warm Spell

Based on the 2003 European heat wave — a year with a very intense single warm spell causing widespread overheating.

DSY3 — 1976

Prolonged Period of Sustained Warmth

Based on 1976 — the longest continuous hot spell in UK records, representing prolonged sustained heat.

Compliance Framework

TM52 Compliance Applied to TM49

The same three TM52 criteria are applied, but using TM49 London weather files. A building fails if any two of the three criteria are not met:

1 Hours of Exceedance — hours where operative temperature exceeds threshold by ≥1 K (May–September).

2 Daily Weighted Exceedance — severity of overheating within any single day.

3 Upper Limit Temperature — absolute maximum daily temperature beyond which overheating is unacceptable.

A room or building that fails any two of the three criteria is classed as overheating.

More about CIBSE TM52

How Can We Help You?

If your project is within the Greater London Authority, we can assist you in assessing the risk of overheating using TM49 weather scenarios and TM52 compliance criteria, producing a GLA-compliant report for planning submission.

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CIBSE TM49Overheating Analysis