Overheating Risk Assessment provides compliant thermal modelling for new residential developments across the UK.

As we specialise in CIBSE TM59 and dynamic simulation modelling, our reports are accepted by planning authorities, Building Control, and design teams.

Since we assess risk early in the design process, clients rely on us to meet regulations and avoid costly changes later.

Request your free, no-obligation quote today.

What Is an Overheating Risk Assessment?

An overheating risk assessment is a compliance report that checks whether a building will experience excessive indoor temperatures under current and future climate conditions.

It uses dynamic simulation modelling (DSM) or the simplified CIBSE TM59 method to assess temperature exposure based on factors like glazing, ventilation, solar gain, and occupancy.

Because overheating is now regulated through Part O of the Building Regulations, the assessment proves thermal comfort is achieved without mechanical cooling.

Since poor thermal performance affects occupant health and planning approval, the assessment is required before construction begins.

When Is an Overheating Risk Assessment Required?

Overheating assessments are required during the design or planning phase for most new residential developments.

They are submitted alongside SAP reports, Part L calculations, and energy strategies.

As Building Regulations and local policies set maximum thresholds for internal heat exposure, the assessment is essential to demonstrate compliance.

Since planning authorities now request these assessments at submission stage, early modelling prevents delays, redesigns, and rejections.

How Much Does an Overheating Risk Assessment Cost?

The overheating risk assessment is between £395 and £1,200 + VAT.

The cost depends on the size and complexity of the development.

Single dwellings or flats usually fall within the £395–£595 range, while larger or multi-unit schemes range from £695 to £1,200.

Costs are influenced by floor area, layout complexity, glazing levels, and ventilation design, we provide fixed-fee quotes based on your drawings.

Since modelling requirements vary between developments, factors like orientation, window types, and passive cooling strategies can affect pricing.

As late-stage design changes are often more expensive, early assessment helps avoid compliance issues and keeps overall project costs down.

What Are the Benefits of an Overheating Risk Assessment?

An overheating risk assessment supports compliance and helps deliver thermally resilient homes from the design stage.

Key benefits include:

• Demonstrates compliance with Part O – The assessment confirms that your design meets overheating limits set by Building Regulations.
• Supports planning and Building Control approval – Overheating analysis is now expected by most local authorities and Approved Inspectors.
• Prevents costly redesigns or delays – Early modelling highlights thermal issues before planning is submitted or construction begins.
• Improves occupant health and comfort – Limiting overheating protects residents from heat stress, especially in summer months.
• Reduces reliance on mechanical cooling – The assessment promotes passive solutions such as natural ventilation and solar control.
• Integrates with energy strategy and SAP reporting – Overheating data aligns with wider regulatory compliance and performance targets.
• Strengthens the planning application – A compliant overheating report adds credibility and supports a smoother approval process.
• Enhances long-term property performance – Thermally efficient buildings are more liveable, durable, and energy-efficient.
• Supports climate resilience – The modelling accounts for future climate scenarios and rising summer temperatures.
• Aligns with Net Zero goals – Reducing demand for cooling supports energy efficiency and decarbonisation targets.
• Minimises future retrofit risk – Addressing overheating during design avoids expensive post-completion fixes.
• Helps prioritise design improvements – Room-level results guide adjustments to glazing, layout, or ventilation strategies.
• Improves comfort in high-risk buildings – Schemes with large glazed areas or urban locations benefit most from early assessment.

Who Needs an Overheating Risk Assessment?

Any new residential development that introduces dwellings will require an overheating risk assessment.

As overheating risk increases in dense, urban sites and buildings with high glazing or limited ventilation, most local authorities request assessments during design.

Since thermal compliance is now a condition of planning approval, the assessment is a core part of the submission package.

What Types of Properties Do You Assess?

We assess detached and semi-detached houses, flats, apartment blocks, student accommodation, HMOs, care homes, and sheltered housing.

We also assess high-glazing schemes, urban infill projects, and developments with restricted natural ventilation.

As overheating risk is higher in buildings with dense layouts, large glazed areas, or limited airflow, the assessment applies wherever thermal compliance must be demonstrated.

What Does Overheating Risk Assessment Involve?

The assessment involves thermal modelling using weather data, layout information, and internal gain assumptions to simulate indoor conditions.

We analyse room-level temperatures using the building’s orientation, window specifications, ventilation strategies, and occupancy profiles.

As this identifies spaces likely to exceed comfort thresholds, it enables passive design adjustments before plans are finalised.

Since performance is affected by multiple factors, detailed modelling is essential for accurate risk analysis.

What Methodology Do We Use?

We use the CIBSE TM59 methodology with dynamic simulation modelling (DSM) to assess compliance with Building Regulations Part O.

This includes testing whether bedrooms and living rooms exceed threshold temperatures during typical summer periods.

Since TM59 is the standard referenced by planning authorities and Building Control, it ensures reports are fully compliant.

As some projects also require adaptive thermal comfort modelling, we provide both standard and extended reporting as needed.

Can We Provide Design Advice if the Assessment Fails?

We provide clear recommendations where thermal performance fails to meet compliance thresholds.

We advise on shading devices, glazing ratios, natural ventilation options, and layout changes to improve comfort.

As these adjustments are modelled in real time, they help avoid planning rejection or future retrofit costs.

Since our reports include actionable guidance, they support effective coordination with architects and engineers.

Do We Work with Architects and Design Teams?

We collaborate directly with architects, M&E consultants, and planning professionals throughout the design process.

We provide early input on layout, ventilation, and orientation to reduce overheating risk.

As thermal compliance often overlaps with SAP and energy strategy requirements, our reports are integrated into broader compliance packages.

Since early coordination reduces rework, we support project efficiency from concept to submission.

Can We Assess Projects at Concept or Feasibility Stage?

We offer early-stage thermal reviews to test layout options, massing, and ventilation strategy before detailed plans are developed.

This supports better passive design choices and reduces risk of non-compliance at later stages.

As overheating is often linked to early design decisions, concept-stage modelling improves long-term outcomes.

Since adjustments are easier and more affordable before planning, feasibility assessments are a practical tool for developers.

How Quickly Can We Deliver the Report?

Standard turnaround is 5 working days.

We fast-track urgent projects to meet planning submission deadlines or late-stage compliance needs.

As planning delays can stall approval, we recommend early booking to guarantee availability.

Since overheating compliance is time-sensitive, our turnaround ensures your project stays on schedule.

What’s the Difference Between Part O and TM59?

Part O defines the legal requirements to limit overheating in buildings, while TM59 provides the assessment method used to demonstrate compliance with Part O.

As TM59 is referenced in official guidance, it is the standard approach for residential overheating assessments.

Since compliance depends on passing TM59 criteria, it forms the basis of our reporting.

Can We Work with Existing or Approved Designs?

We assess existing designs and provide compliance checks for schemes already submitted or approved.

We model the design as-is and offer improvement strategies if thermal issues are identified.

As late-stage modelling can uncover non-compliance, it’s important to act before final approval.

Since Part-O enforcement is increasing, checking approved plans for thermal risk is often worthwhile.

Are Overheating Risk Assessments Required for Single Dwellings?

Overheating assessments are required when a single dwelling has features that increase internal heat risk.

As high glazing ratios, limited ventilation, or urban location reduce natural cooling, compliance must be demonstrated at the planning stage.

Since Part O applies to all new residential buildings, even individual homes must show thermal performance.

Do Permitted Development Projects Require Overheating Assessments?

Overheating assessments are required for permitted development schemes that introduce residential units.

Since prior approval does not exempt compliance with Building Regulations, thermal modelling is still needed.

As conversions and rooftop extensions often lack effective ventilation or solar control, overheating risk is higher.

Can We Assess the Residential Part of a Mixed-Use Development?

Only the residential portion of a mixed-use scheme is included in the overheating assessment.

As habitable rooms are regulated under Part O, bedrooms and living spaces must be modelled for compliance.

Since commercial areas follow different standards, they are excluded from the report.

Does the Assessment Consider Future Climate Conditions?

Overheating assessments include future weather scenarios to reflect changing climate risk.

Since TM59 requires testing under future climate projections, weather files are selected based on regional climate data.

As overheating frequency will rise over time, future performance must be accounted for at the design stage.

Can We Compare Multiple Design Options?

The assessment can model alternative layouts or strategies to support early-stage design decisions.

As orientation, glazing, and ventilation affect results, testing different options helps optimise performance.

Since design choices made early are cheaper to adjust, comparative modelling reduces long-term cost and risk.

What Happens if the Design Fails the Assessment?

The report includes recommendations where overheating limits are exceeded.

Since shading, window sizing, or ventilation adjustments can improve performance, these measures are tested to meet compliance.

As resubmission is often required for approval, revised models confirm the updated design meets TM59 thresholds.

How Do Glazing Ratios Affect Overheating Risk?

High glazing ratios increase the risk of overheating in habitable rooms.

Since larger glazed areas admit more solar gain, they raise internal temperatures during peak summer periods.

As TM59 requires specific limits for solar exposure, designs with extensive glazing must be modelled carefully to avoid non-compliance.

Are Top-Floor Flats at Higher Risk of Overheating?

Top-floor flats are more likely to overheat compared to ground-floor units.

As they receive more direct sunlight and often have limited cross-ventilation, internal heat can build up more quickly.

Since planning authorities recognise this risk, assessments typically highlight top-floor units as priority areas for mitigation.

Can Overheating Assessments Be Combined with SAP or SBEM?

Overheating assessments are separate from SAP and SBEM but can be coordinated alongside them.

Since each report uses different modelling approaches and inputs, results must be integrated carefully for consistency.

As overheating results impact design choices, combining reports improves compliance coordination and reduces project risk.

Are Certain Ventilation Strategies More Likely to Pass TM59?

Natural and hybrid ventilation strategies are often more successful in meeting TM59 thresholds.

Since passive airflow helps remove excess heat, well-designed natural systems improve compliance outcomes.

As mechanical cooling is discouraged under Part O, ventilation performance plays a key role in thermal modelling.

Can We Assess Post-Planning Changes to Design?

Design revisions made after planning can be re-assessed to ensure compliance is maintained.

As alterations to glazing, layout, or orientation affect internal temperatures, updated modelling is often required.

Since Building Control reviews the final version, the overheating assessment must reflect the approved construction drawings.

How Do I Book an Overheating Risk Assessment?

To request a free site survey, simply send your floor plans, elevations, and basic project details via our contact form.

We review your project and provide a fixed quote with a timeline.

Since local authorities are enforcing compliance more strictly, timely submission prevents costly delays.

Schedule a free consultation today.

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