Understanding Building Regulations Part 0: What it Means for Sustainable Design
What is Part O and why was it introduced?
Part O of the Building Regulations was introduced on 15 June 2022, with a one-year transition period ending on 15 June 2023. It was created to tackle the growing risk of overheating in new homes and sets out strategies for natural cooling and purge ventilation, particularly in dwellings with significant areas of glazing.
For practices like ARCO₂, this is especially relevant. Many of our projects are located in stunning Cornish landscapes, where maximising natural light and framing panoramic views is central to the architecture. While we have never advocated for wall-to-wall glass as a blanket solution, generous glazing is often a key part of our designs – bringing the outside in, celebrating views, and flooding homes with daylight
What challenges does Part O bring?
The regulation requires us to prove that new dwellings won’t overheat – which sounds straightforward, but in practice the industry has been caught out. At present, there is no universally adopted software for demonstrating compliance, leaving many practices unsure how to meet the requirement. For Cornwall, with its mix of coastal sun, heavy rainfall, and high winds, getting this balance right is particularly important.
How ARCO₂ has adapted
Fortunately, ARCO₂ has been working to Passivhaus principles for many years. Our designs have always prioritised comfort, energy efficiency, and resilience, which naturally aligns with Part O. We use:
Deep overhangs and brise-soleils for solar shading.
Careful glazing design, ensuring homes are bright in winter but protected in summer.
Super insulation and airtight construction, meaning our buildings need minimal solar gain to stay comfortable.
When Part O came into force, we invested around four weeks developing a robust reporting package to evidence compliance. Backed by data, calculations, and tailored software, this fact-based report has since been approved by Cornwall Council Building Control. It now forms part of every submission we make. https://www.cornwall.gov.uk/planning-and-building-control/building-control/
https://energysavingtrust.org.uk/passivhaus-what-you-need-know/
A case in point: Mawgan Porth
Our recently completed project at Mawgan Porth is a great example of how solar shading can work beautifully in practice. Large overhangs not only protect the interiors from overheating but also provide sheltered outdoor spaces – perfect for enjoying the Cornish coast in rain or shine. 
Even with the sliding doors open, the house remains comfortable, while connecting the interiors to the sound and atmosphere of the ocean.
https://www.arco2.co.uk/sustainable-architecture-projects/architect-mawgan-porth-keynvor/
Although Part O came into force after this project was completed, it stands as a demonstration of the design strategies we have long championed – and which now form the backbone of compliance with the new regulation.
