Overheating Assessments

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What Is an Overheating Assessment?

An overheating assessment evaluates whether a dwelling is likely to experience excessive internal temperatures during summer conditions.
Assessments consider factors such as:

Glazing size and orientation
Solar gains
Ventilation strategy
Shading measures
Building location and noise constraints

The assessment determines whether the dwelling complies with Approved Document O or whether design changes are required to reduce overheating risk.

When Is an Overheating Assessment Required?

Overheating assessments are required for:

Overheating Assessments & Part O Compliance Routes Approved Document O provides two compliance routes:

New Build Dwellings

All new residential buildings must demonstrate compliance with Part O.

Residential Conversions

- Office-to-residential conversions - Warehouse and industrial conversions - Change of use developments

Developments with High Overheating Risk

- Large areas of glazing - South- or west-facing elevations - Single-aspect flats - · Urban locations with high noise levels

Simplified Method (Part O Methodology)

The simplified method uses defined criteria to determine whether a dwelling meets Part O requirements.
This method assesses:

Maximum glazing limits
Minimum opening areas
Orientation of habitable rooms
Provision of shading

If all criteria are met, the dwelling is deemed compliant without dynamic modelling.

Dynamic Thermal Modelling (TM59)

Where the simplified method cannot be met, a dynamic thermal model is required using TM59 methodology.
TM59 assessments simulate:

Hour-by-hour internal temperatures
Occupant behaviour
Weather data
Ventilation and shading performance

TM59 is typically required for:

High-risk dwellings
Single-aspect flats
Noisy urban locations
Large glazed areas

Overheating Assessments for Flats & Apartments

Flats are particularly susceptible to overheating due to:

Limited cross-ventilation
High glazing ratios
Upper-floor heat gain

Overheating assessments for flats focus on:

Room orientation
Window opening strategies
Night-time ventilation
Noise-restricted ventilation scenarios

Where simplified compliance cannot be achieved, TM59 modelling is used to demonstrate acceptable performance.

Overheating Assessments for Houses

Houses often achieve compliance through the simplified method, particularly where:

Cross-ventilation is available
Buildings undergoing major refurbishment
Shading is incorporated

However, TM59 modelling may still be required where:

Large expanses of glazing are proposed
Bedrooms are predominantly single-aspect
Design constraints limit ventilation

Design Stage Overheating Assessments

Overheating assessments are carried out at design stage, allowing overheating risk to be addressed early.

Design Stage Outputs:

Part O compliance assessment
Identification of overheating risks
Clear recommendations for improvement
Confirmation of compliance route used

Early assessment avoids late-stage design changes and helps maintain planning and build programmes.

Common Overheating Mitigation Measures

Where overheating risk is identified, practical and cost-effective measures may include:

· Reducing glazing areas
· Introducing external shading
· Improving natural ventilation
· Adjusting window opening sizes
· Optimising room layouts

The focus is on passive solutions, avoiding unnecessary reliance on mechanical cooling.

Overheating Assessments & SAP Calculations

For new build and converted properties, EPCs are closely linked to:

Energy performance
Carbon emissions
Part L compliance

A coordinated approach ensures:

Part O compliance without compromising Part L
No conflicting design requirements
Smooth Building Control approval

Overheating Assessments for Developers & Designers

This service supports:

Property developers
Architects
Design & build contractors

Overheating assessments are provided for:

Single dwellings
Multi-unit residential developments
Large apartment schemes

Clear reporting helps teams respond quickly to Building Control feedback.

What Information Is Required?

To complete an overheating assessment, the following information is typically required:

Architectural drawings
Glazing schedules
Ventilation strategy
Site location and orientation
Noise constraints (if applicable)

Any missing information is identified early to avoid delays.

Building Control & Overheating Assessments

Overheating assessment reports are issued in a format suitable for:

Local authority Building Control
Approved inspectors

Reports clearly state:

Compliance route used
Assessment methodology
Pass / fail outcome
Any mitigation measures required

Relationship to Other Compliance Services

Overheating assessments often sit alongside:

SAP calculations
BREL / Part L documentation
SBEM calculations (mixed-use developments)
Air tightness testing

Managing these services together reduces compliance risk and improves efficiency.

Why Use a Specialist Overheating Assessment Service?

Experienced Part O assessors

TM59 modelling where required

Clear, Building Control-ready reports

Practical, build-friendly advice

Fast turnaround

The emphasis is on achieving compliance without unnecessary redesign.

Overheating Assessments for Building Regulations Part O Compliance