Defeating Overheating

TuffX’s Commercial Director, Paul Higgins, explains what the building regulations part O means for glass and glazing in new homes, especially when it comes to the company’s speciality – rooflights.

As the first regulation of its kind in England, house builders need to be clear about what is and isn’t affected when it comes to choosing glazing for their projects.

In a nutshell, part O seeks to ensure that the design and construction of new residential buildings limit unwanted solar gain in summer and provide adequate means to remove heat from the indoor environment.

The part O regulations are designed to protect people’s health and welfare by reducing the occurrences of high indoor temperatures in the face of rising global temperatures and the frequency of extreme events such as heatwaves.

Along with the rest of the new building regulations, part O came into force in June and shortly after our UK summer arrived with temperatures reaching 40°C, cementing the urgent and necessity for this.



We are now in the one-year transition period after the new Building Regulations came into effect, to allow for planning applications that are already underway. Any schemes where full plans or a building notice was submitted ahead of 15 June 2022 can be built to previous regulations if work starts within 12 months.


Routes to compliance

There are two routes to Part O compliance - the Simplified Method and the Dynamic Thermic Modelling method. For single dwellings such as new homes, the Simplified Method is most likely to be used, with the Dynamic Thermal Modelling more likely to be used for blocks of flats, single aspect dwellings or buildings with more complex design requirements.


Simplified Method

For the Simplified Method, part O sets out tables detailing maximum permitted glazed areas, taking into consideration the location of the building and whether it has cross ventilation. Buildings in high-risk areas. Currently specific postcodes in central London and Manchester may also need to provide shading for glazed areas at certain points (means for achieving which, such as external shutters and overhangs, are detailed in the approved document).


Solar solutions

High-quality solar glass products will play an important part in achieving these new standards. By using a tinted coating on the exterior of the glass to reflect heat away from the interior, solar glass allows an ambient interior temperature to be achieved, reducing the need for expensive air conditioning.


Infinity rooflight

It is possible to fit solar glass that reflects twice as much heat as standard glass. For example, with the approved document part O in mind, TuffX has specifically developed a new rooflight for our Infinity range that achieves this through a new coating. Unlike most solar glass it is untinted, so it achieves maximum light transmission too.


Consumer demands

Because while ensuring your rooflights and windows meet the new regulations, it’s important to also make sure they meet – and ideally exceed – the high standard of quality a new homeowner expects including maximising light transmission, being easy to maintain and looking great.

And of course, come winter, energy efficiency will be imperative, so make sure your glass products achieve the lowest U-values too. Our new rooflight has a U-value of 1.0, making it, in my opinion, the UK’s most energy efficient all year-round offering.


Picture: TuffX’ Infinity rooflight.

Article written by Cathryn Ellis
16th February 2023


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