Abstract

Since the introduction of Approved Document O (Part O) on 15 June 2022, all new residential buildings in the UK must be assessed for overheating risk during the design and pre-construction stages.

One of the recognised approaches is the Dynamic Thermal Modelling Method (DTMM), which follows the guidance outlined in CIBSE Technical Memorandum TM59. This methodology is widely used by building performance consultants and sustainability engineers to assess overheating risk in residential buildings, including Purpose-Built Student Accommodation (PBSA) developments.

This paper investigates the impact of modelling inputs on overheating assessment outcomes. In particular, it evaluates whether some standard TM59 assumptions may lead to over-engineered building strategies, potentially increasing energy demand and carbon emissions in PBSA developments.

The research aims to determine whether adjustments to standard modelling inputs could improve energy efficiency and overheating mitigation strategies, while maintaining occupant thermal comfort.

Methodology and Case Study

The findings presented in this study are based on a detailed case study of a PBSA development used for planning and overheating compliance assessments.

The modelling adjustments applied in this analysis are informed by the authors’ experience assessing numerous PBSA schemes using dynamic thermal modelling tools. The research evaluates standard TM59 modelling inputs, compares them against modified assumptions reflecting realistic building use, and assesses how these differences affect overheating compliance results.

This analysis represents an initial step toward improving early-stage overheating modelling practices. The findings aim to support future research and industry discussion on how modelling assumptions could evolve to better reflect real-world building operation and occupancy patterns.

Results and Discussion

The results of the modified modelling templates show notable differences when compared with those produced using standard TM59 assumptions.

The adjusted internal heat gain profiles demonstrate consistently lower internal heat loads in the assessed rooms compared with the standard templates. The most significant differences occur in communal kitchens, followed by studio units.

These variations also influence the overall overheating compliance rate across the three room types analysed.

Although bedrooms show a similar level of TM59 compliance in both modelling approaches, the communal kitchens and studio units display significant differences in overheating performance.

Further analysis highlights substantial variation between the best- and worst-performing rooms relative to the TM59 overheating threshold, indicating that modelling assumptions can strongly influence the perceived overheating risk.

Conclusion

The findings suggest that customised, data-driven occupancy and internal heat gain profiles may provide a more accurate representation of actual building use in PBSA developments than the current default TM59 modelling assumptions.

Adopting more realistic modelling inputs could improve the accuracy of overheating risk assessments, while supporting more energy-efficient building design strategies that maintain occupant thermal comfort without relying on excessive mechanical cooling.

This approach aligns with the growing need for low-carbon, climate-resilient building design and highlights the potential for future refinement of overheating modelling methodologies used in early-stage building assessments.