Thermal Comfort & Overheating

Part O, CIBSE TM52 and TM59 overheating risk screening for planning submissions

Building Details

Building Type

Determines ventilation potential and solar exposure characteristics

Number of Bedrooms

Required for TM59 Criterion B assessment

Dwelling Floor Area (sqm)

Gross internal area of the dwelling

Floor Position

Top floors have increased roof exposure

Primary Facade Orientation

Direction of main glazed facade

Location Zone

Urban Heat Island effect varies by location

Glazing Characteristics

Glazing Ratio (% of facade)

Percentage of facade that is glazed (typical 20-40%)

Glazing Type

Affects solar transmittance

Solar Heat Gain Coefficient (g-value)

Typical values: Clear 0.75, Low-E 0.3-0.4, Tinted 0.2. Default 0.4 for standard double glazing

Ventilation Strategy

Primary Ventilation Method

Cross-ventilation and mixed-mode provide best cooling

Secure night-time ventilation available

Can windows be left open safely overnight for free cooling?

External noise prevents window opening

Road or rail noise limits natural ventilation cooling

Solar Shading

External Shading

External shading is highly effective; internal blinds less so

Internal blinds fitted

Internal blinds provide partial additional shading

Nearby Shading (Surrounding Landscape/Buildings)

East/west facades benefit most from tree or building shading

Building Construction

Thermal Mass

Higher mass dampens temperature swings

Insulation Level

Better insulation reduces thermal bridging

Roof Type (if top floor or sloped)

Green roofs provide significant thermal mass and evaporative cooling

Part O Compliance & Active Cooling

Part O Overheating Zone

Part O defines zones by overheating risk; Zone 2 requires more stringent assessment

Active cooling system planned (A/C or Chiller)

Active cooling significantly reduces overheating risk

Heat Balance Summary

Solar Gain (W)	-
Location UHI Multiplier	-
Adjusted Solar Gain (W)	-
Ventilation Cooling Capacity (W/sqm)	-
Thermal Mass Damping Factor	-
Net Heat Balance	-

Overheating Risk Score (0-100)

TM59 Overheating Criteria Assessment

Criterion A (Living Rooms/Kitchens/Bedrooms)

Part O Building Regulations - Overheating Risk Screening

Planning Submission Guidance

Contributing Risk Factors (Ranked by Impact)

Design Recommendations

About this tool: Overheating

Part O overheating compliance — CIBSE TM52/TM59 methodology, solar gain analysis, ventilation strategy, shading requirements, and dynamic thermal modelling triggers.

When to use it

Required for all new residential buildings since June 2022. Part O sets maximum internal temperatures and requires specific design responses.

Policy and guidance it draws on

Building Regs Part O, CIBSE TM52/TM59

Part of Environmental Intelligence

Use these tools when preparing technical reports and compliance documentation. Many of these are validation requirements — submit without them and your application will be returned. Use the Validation Pre-Flight tool to check which ones you actually need.

Guidance to help you prepare — not formal planning advice. Check the current policy text and your council's local plan before relying on it.