Part O & TM59 Compliance for Domestic and Commercial

Overheating Assessments

Professional overheating risk assessments for Building Regulations compliance. Part O for domestic, TM52/TM59 for commercial and complex residential.

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Overheating Assessments

What is an overheating assessment?

Checks that buildings won't get too hot in summer. Required for new homes and many commercial buildings.

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Do I need Part O?

All new dwellings in England need Part O compliance since June 2022.

Part O explained →

What about commercial?

Schools, care homes, offices often need TM52 assessment for BREEAM or planning.

TM52 for commercial →

Simplified or dynamic?

Part O simplified works for most homes. Complex designs need dynamic simulation.

Which method? →

How much does it cost?

Part O simplified from £95. Dynamic modelling from £250.

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How long does it take?

Simplified same-day. Dynamic modelling 2-4 working days.

See process →

Not sure which assessment you need? Send us your plans and we'll confirm the right approach.

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2-4 day turnaround Elmhurst OCDEA

What Is an Overheating Assessment?

An overheating assessment checks whether a building will remain comfortable during hot weather without relying on mechanical cooling.

As buildings become more insulated and airtight, and as summers get hotter, overheating has become a genuine concern. Highly glazed, south-facing rooms can reach uncomfortable or even dangerous temperatures.

Building Regulations now require overheating assessments for most new buildings. The assessment checks factors like glazing orientation, ventilation strategy, solar shading, and thermal mass to predict whether rooms will overheat and recommend mitigation if needed.

Which Overheating Assessment Do You Need?

The assessment method depends on your building type and complexity.

Part O (Domestic)

Required for all new dwellings in England since June 2022. Most pass using the simplified method.

Part O Assessments →

TM52 (Commercial)

Dynamic simulation for schools, offices, care homes. Required for BREEAM and many planning conditions.

TM52 Assessments →

When Is an Overheating Assessment Required?

Overheating assessments are required in various scenarios:

Part O (Domestic)

  • ✓ All new dwellings in England
  • ✓ Required since 15 June 2022
  • ✓ Alongside SAP for Building Control
  • ✓ Applies to houses, flats, conversions

TM52/TM59 (Dynamic)

  • ✓ Complex residential with high glazing
  • ✓ Schools and educational buildings
  • ✓ Care homes and healthcare
  • ✓ BREEAM requirements

Planning Conditions

  • ✓ Often required for major developments
  • ✓ Listed as condition on planning approval
  • ✓ May specify TM59 or Part O compliance
  • ✓ Can be required before construction starts

Overheating Assessment Pricing

Pricing depends on assessment type and building complexity.

Part O Simplified

From £95

Prescriptive check for standard dwellings. Same-day results.

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Part O / TM59 Dynamic

From £250

Dynamic simulation for complex domestic designs.

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TM52 Commercial

From £350

Dynamic simulation for schools, offices, care homes.

Learn more →
View Full Pricing →

How Overheating Assessments Work

The process depends on which assessment type you need.

  1. 1

    Send us your drawings

    Floor plans, elevations, glazing schedule, ventilation strategy. We'll confirm which assessment applies.

  2. 2

    We complete the assessment

    Simplified checks are same-day. Dynamic modelling takes longer but provides more detailed results and design flexibility.

  3. 3

    Receive your report

    Clear pass/fail result with recommendations if needed. Reports formatted for Building Control or planning submission.

Why Choose Us for Overheating Assessments

We provide practical advice, not just a pass/fail report.

What You Get

  • Qualified assessor with thermal modelling experience
  • Clear reports for Building Control
  • Practical mitigation recommendations
  • Fast turnaround times
  • Fixed, transparent pricing
  • Email support throughout

What You Avoid

  • Overly conservative assumptions
  • Unnecessary mechanical cooling recommendations
  • Confusing technical reports
  • Weeks of waiting
  • Hidden fees
  • Revision charges

Overheating Assessment FAQ

Do all new homes need Part O?
Yes. All new dwellings in England require Part O compliance since 15 June 2022. This includes houses, flats, conversions, and buildings created by change of use.
What's the difference between simplified and dynamic?
The simplified method is a prescriptive check based on glazing limits and ventilation requirements. Dynamic modelling simulates the building hour-by-hour through a design summer year, giving more accurate results and design flexibility.
When do I need dynamic simulation instead of simplified?
When the simplified method fails, when design has high glazing or limited ventilation, or when the project is complex (single-aspect flats, buildings with noise constraints). Some planning conditions also specify dynamic modelling.
Can overheating assessment be done alongside SAP?
Yes, and this is the normal approach. We often complete SAP and Part O together for new dwellings, using the same drawings and specification.
What happens if my building fails?
We provide recommendations to achieve compliance - typically adjusting glazing sizes, adding solar shading, improving ventilation, or increasing thermal mass. All reasonable revisions included.

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All overheating assessments completed by qualified assessors and accepted by Building Control nationwide.