Delivering CIBSE TM59 dynamic thermal modelling to secure Part O compliance without compromising design.
Project Overview
- Client: Redrow Homes South Wales
- Sector: Private Residential / New Build
- Location: Hendredenn, Caerphilly, Wales
- Services Provided: Part O Overheating Compliance, CIBSE TM59 Dynamic Thermal Modelling
- Scale: 260 dwellings – two-storey houses and maisonettes across multiple house types
- Target: Compliance with Approved Document Part O (2022 Wales Edition)
The Challenge
Part O of the Building Regulations was introduced to manage the health risks of overheating as the climate changes, and it’s fundamentally changed how new homes get designed. For Redrow’s De Clare Gardens development, that presented a real problem: several of the house types on site – including the Yew, Hornbeam and Rowan types – feature large, complex glazing arrangements as part of their design appeal. Assessed under the standard “Simplified Method” for Part O, these highly glazed homes would have failed outright, with the standard remedy being smaller windows – directly undermining the architectural design Redrow had built the development around.
The Solution
CIBSE TM59 Dynamic Thermal Modelling
Rather than relying on the Simplified Method’s blanket assumptions, we built detailed dynamic thermal models of each house type, simulating real hour-by-hour thermal performance across a full year using accurate glazing data rather than the Simplified Method’s punitive defaults. Initial modelling flagged a number of plots at risk of overheating, concentrated mainly in bedrooms with restricted window openings. Rather than a blanket fix, we worked through the qualifying house types individually, resolving most through increased window opening area alone – with no change to window size or glazing – and finding a bespoke solution for the one house type that needed it, without compromising the design that made it distinctive. Throughout, we worked closely with Redrow’s technical team to keep every proposed change buildable and cost-effective.
Dynamic Thermal modeling provides a powerful tool to ensure that the homes we built today are not only energy efficient but are also prepared to deal with the future challenges of changing climates by using advanced software to allow for design flexibility, and the use of glazing properties and shading that is not used in the simplified overheating method.
— Richard Millard, Lead sustainability Consultant at Building Energy Experts
The Outcome
Every one of the 260 plots across De Clare Gardens achieved full Part O compliance – including the most heavily glazed house types – without shrinking a single window. Redrow received detailed, plot-by-plot TM59 reports giving Building Control clear, robust evidence to support approval without delay, and their design team was able to finalise house types and site layouts already knowing overheating risk was fully resolved. It’s a clear demonstration of what dynamic thermal modelling can do that a simplified assessment can’t: find a compliant, cost-effective path for every single plot, rather than forcing a compromise on the ones that don’t fit the standard assumptions.
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
