Approved Document [X/S] is not the end of the road for highly glazed house design.

There has been a lot of talk in our offices about the proposed addition to England's building regulations; Approved Document [X/S] (as yet unnamed). This new section of building regulations is currently in its consultation period (ending 13th April 2021) and is designed to address the issues of overheating in residential design.

Overheating in houses is an important issue, especially with the increased temperatures we are experiencing in the summer months. It is reported that there are approximately 2,000 heat-related deaths in England and Wales each year [1], most of which occur in their own homes. With increasing temperatures this number is set to rise.

The new addition to Building Regulations (which only applies to new build dwellings and residential properties) details the ways in which overheating can be addressed in building design. These include,

• considering the size and orientation of the glazing,
• including solar control or shading methods on critical elevations.

But it is important to understand that these new proposed guidelines do not restrict or prohibit the use of large glass elevations in contemporary house design.

The draft Approved Document (AD ‘X’ in England, AD S in Wales) doesn’t ban glass facades, doesn’t force you to use smaller windows and doesn’t control the orientation of new buildings. [2]

The proposed Approved Document offers two routes to compliance, in a similar way in which Part L1A offers various ways to show compliance for thermal insulation.

The 'Simplified Method' looks at the glazed area vs the floor area, restricting glass elevations to 13-21% of the floor area (depending on the project type and location).

(My explanation of the 'simplified method' is also greatly simplified. You also have to determine what 'Group' the building belongs to dependant on the number of fabric elements and whether there are openings on opposite elevations. Buildings in Greater London have additional shading requirements for critical elevations. Glazing should also be evenly distributed across all elevations OR be concentrated on the North and East facing sides. There are also requirements for the size of opening elements to allow heat to escape.)

These simplified guidelines offer a quick and efficient route to building compliance to house designers and builders who want a simple solution.

However, architects and designers looking for a more flexible approach to building design can do so using the 'Dynamic Thermal Analysis' method. This more open design method uses an adapted version of the CIBSE's TM56 methodology for predicting risk of overheating paired with various strategies for reducing overheating risks.

This then puts the design of the building back in the architect's hands. Allowing them to design a home to suit their client's specification as well as being comfortable, safe and useable throughout the year.

Some of the strategies put forward to reducing solar gain in summer include:

• the inclusion of overhangs or protruding reveals around windows
• considering the orientation of the glazing
• specifying glass with a high g-value to reduce solar gain
• using other building structures to provide shade.

It cannot be denied that this addition to Building Regulations will change the way in which highly glazed homes are designed. However, this focus on reducing overheating will result in homes that are better equipped to deal with increasing temperatures, in buildings that are more comfortable and even more exceptionally designed architectural structures.

The proposed document is not yet in effect but if you are worried about the impact these new rules will have on your proposed design the team at IQ are happy to talk to you. Get in touch.

[1] "Building envelope design in London is about to change radically", AJ Online, Geoff Wilkinson. [2] "New Overheating Regulations – Do I need to design my next site with smaller windows?", Energist, Jon Ponting.