Part O Simplified Method overheating assessments provide a fast, recognised route to demonstrating compliance with UK overheating regulations at the planning and Building Control stage.
At Compliant EPC, we deliver Part O Simplified Method assessments for developments that include dwellings or rooms for residential purposes, including apartments, student accommodation, hotels, and mixed-use schemes where residential accommodation forms part of a wider commercial project.
Our assessments confirm that a building can effectively limit unwanted solar gains and remove excess heat, helping design teams achieve compliance without the cost, programme impact, or complexity of full dynamic thermal modelling when it is not required.
Based in Nottingham, we support projects across the East Midlands and the UK, providing clear, compliance-ready reports suitable for planning submissions and Building Control approval.
Part O of the Building Regulations applies to dwellings and rooms for residential purposes. The Simplified Method is an accepted compliance route for residential spaces where building form, glazing, and ventilation strategies fall within defined limits.
This commonly includes:
Where a scheme includes non-domestic spaces such as offices, education or healthcare areas, overheating risk for those parts of the building is typically assessed using CIBSE TM52, while residential-type accommodation may also require CIBSE TM59.
For mixed-use projects, we coordinate Part O, TM52 and TM59 assessments to deliver a joined-up overheating strategy that satisfies planners, Building Control and design teams without conflicting assumptions or unnecessary redesign.
The Part O Simplified Method uses prescribed limits and design criteria to verify that the risk of overheating remains within acceptable thresholds. It focuses on a building’s ability to:
Our assessment review:
This approach is particularly well-suited to low- and medium-risk residential elements within commercial and mixed-use schemes, providing a robust and cost-effective alternative to dynamic modelling when the simplified criteria are met.
Where a design exceeds simplified method limits, we advise early and transparently, allowing the project team to move smoothly to TM52 or TM59 modelling without abortive work.
The Part O Simplified Method is not a modelling exercise. It is a rule-based, checklist-compliance route defined in Approved Document O that uses prescribed limits for glazing, ventilation, and dwelling layout to determine whether the overheating risk is acceptable without dynamic thermal simulation.
This is a deemed-to-satisfy approach. If a design falls within the stated limits, overheating compliance can be demonstrated without TM59 modelling.
Approved Document O sets maximum glazing area limits based on each façade’s orientation. South- and west-facing elevations are more restricted due to higher solar gains, while north-facing glazing is treated more leniently.
We assess:
Excess glazing on high-risk façades is one of the most common reasons projects fall outside the Simplified Method.
Single-aspect dwellings are treated as higher risk because they lack cross-ventilation. Approved Document O places stricter limits on glazing and ventilation openings for these layouts.
Dual-aspect dwellings benefit from cross-ventilation, allowing more effective removal of excess heat and greater flexibility within glazing limits.
A key requirement of the Simplified Method is demonstrating that windows provide sufficient ventilation through their Equivalent Area (EA) and free opening area.
This is not simply a window size. It is calculated from:
Demonstrating adequate EA proves that excess heat can be removed without mechanical cooling.
Approved Document O requires dwellings to rapidly remove built-up heat through purge ventilation, particularly during cooler night-time periods.
We verify that window openings and the layout allow effective night-purge ventilation.
Where façades are exposed to high external noise levels, windows may not be opened to a reasonable extent. Approved Document O recognises this and applies additional restrictions in urban or high-noise locations.
In these cases, the Simplified Method may no longer be suitable without alternative ventilation strategies.
The Simplified Method also considers whether a site is classed as a moderate or high overheating risk location, influenced by the urban heat island effect and local climate data.
These categories directly affect allowable glazing limits and ventilation requirements.
The Simplified Method works as a clear pass/fail checklist. If a design stays within the prescribed limits for:
Overheating compliance can be demonstrated without simulation.
Glazing design is one of the most critical factors in meeting the Part O Simplified Method. Excessive or poorly distributed glazing can significantly increase solar gains and the risk of overheating, particularly on south- and west-facing façades.
Our assessments verify that:
Ventilation strategy is assessed alongside glazing to ensure excess heat can be removed effectively through:
Optimising glazing and ventilation early in the design process reduces reliance on mechanical cooling and supports compliance in a cost-effective, buildable way.
In commercial and mixed-use schemes, residential accommodation often sits alongside offices, retail, education or healthcare spaces. While Part O applies only to residential areas, overheating compliance is increasingly expected across the entire development.
We regularly support schemes where:
By coordinating these assessments, we ensure a consistent set of assumptions around climate data, internal gains and ventilation strategies, reducing the risk of contradictory outcomes and planning objections.
We make overheating compliance straightforward through a clear, structured process:
We review your drawings, design intent and site context to confirm whether the Part O Simplified Method is appropriate or whether dynamic modelling is likely to be required.
We gather all relevant information, including:
We assess solar gains, ventilation potential and compliance thresholds. Where risk is identified, we provide clear, practical recommendations such as:
You receive a professional overheating compliance report suitable for planning and Building Control submission, clearly setting out assumptions, calculations and mitigation measures.
We support your team through design changes, re-assessments and compliance sign-off to ensure overheating risk remains controlled through to construction.
Our Part O Simplified Method reports are produced in line with current regulatory guidance and are suitable for submission to local planning authorities and Building Control bodies.
We have experience supporting approvals for:
Our clear reporting approach reduces queries, delays and redesign risk at later project stages.
From concept design to as-built stages, we help ensure overheating risk is addressed in a practical, proportionate and compliant manner.
Our aim is to make overheating compliance simple, robust and commercially sensible.
Part O applies to dwellings and rooms for residential purposes. In commercial or mixed-use schemes, residential areas must comply with Part O, while non-domestic spaces are typically assessed using TM52.
It uses prescribed limits for glazing, orientation, and ventilation to demonstrate that the risk of overheating remains acceptable without complex modelling.
For large or complex buildings, extensive glazing, limited ventilation or high internal gains, TM52 or TM59 modelling provides a more appropriate assessment route.
Yes. Demonstrating thermal comfort and overheating mitigation can contribute to BREEAM Hea and Ene credits.
Simplified Method assessments are often completed within a few days. Dynamic modelling typically takes one to two weeks, depending on complexity.
Avoid costly redesigns, reduce planning risk, and deliver comfortable residential spaces that meet UK overheating regulations.
Contact Compliant EPC today for expert Part O Simplified Method overheating assessments, a fast, reliable route to compliance for residential and mixed-use developments.
Ready to ensure your building is cool and compliant with Part O? Contact us today to schedule your assessment or to learn more about our services.
Have a question or need assistance? We’re here for you. Just send us a message, and we’ll get back to you promptly.
To discuss your project or specific requirements further or for a FREE quotation please contact us.
01623 573009 
contact@compliant-epc.co.uk 
