Applying CIBSE TM59 dynamic thermal modelling across two very different building typologies on one site.
Project Overview
- Client: Redrow Homes South Wales
- Sector: Private Residential / New Build
- Location: North of Lisvane, Cardiff, Wales
- Services Provided: Part O Overheating Compliance, CIBSE TM59 Dynamic Thermal Modelling
- Scale: 23 dwellings – two apartment blocks (ground, first and second floor flats) and five houses, Phase 2D, Plots 695–717
- Target: Compliance with Approved Document Part O (2022 Wales Edition)
The Challenge
Part O compliance is rarely a one-size-fits-all exercise, and Churchlands put that to the test in a single assessment. The development combined two apartment blocks – each with multiple floor levels and a range of window sizes and restricted ground-floor openings – alongside a run of houses with their own distinct glazing and ventilation strategy. Apartments bring their own overheating risk profile: smaller opening areas, party floors and walls affecting heat retention, and less scope for the kind of cross-ventilation houses can rely on. Modelling both typologies accurately, without defaulting to a blanket approach, meant treating each block and house type on its own terms.
The Solution
CIBSE TM59 Dynamic Thermal Modelling
We built dynamic thermal models in DesignBuilder EnergyPlus for every plot across both apartment blocks and the house types, using the Cardiff DSY1 2020 High 50 weather file in line with CIBSE TM59 and Part O (Wales). For the apartment blocks, this meant modelling floor-by-floor variation in opening area and restricted versus unrestricted openings – ground floor units needed TM59-restricted opening assumptions, while upper floors could rely on unrestricted natural ventilation. For the houses, we applied the same rigour to their own glazing and opening schedules. Running both typologies through one coordinated assessment gave Redrow a single, consistent set of evidence covering the full mix of unit types on the development.
The Outcome
All 23 dwellings across Churchlands – apartments and houses alike – achieved full Part O compliance, with results showing no overheating risk across any plot or zone. Redrow received clear, plot-by-plot TM59 reporting that Building Control could rely on across the whole development, regardless of unit type. It’s a good example of what a single dynamic thermal modelling exercise can flex to cover: apartment blocks and houses assessed to the same standard, on the same site, without treating either as an afterthought.
Client Testimonial
We’ve worked with Building Energy Experts to support Part O compliance across our developments and have been consistently impressed with their service. Their team is proactive, knowledgeable, and always on hand to provide clear guidance throughout the design and compliance process.
Their reports are thorough yet easy to digest, and their input has been instrumental in helping us meet regulatory requirements without compromising on design. The quality of their reporting and technical advice has made them a valuable partner to our team.
— Sean Haplin, Technical Coordinator, Redrow Homes
