It is a great delight to see the most essential of buildings, the house, awarded the Stirling Prize.
House design is rarely celebrated, yet homes influence almost every aspect of our lives and are intrinsically linked to our mental and physical wellbeing. In the words of the judges, the homes at Goldsmith Street represented “high-quality architecture in its purest, most environmentally and socially conscious form”. They are a “modest masterpiece”.
And while the aesthetics have been lauded, as much weight has been given to the sustainability of the project.
The homes have been built to Passivhaus standards, that considered the orientation of the street and pitch of the roofs to maximise energy from the winter sun as well as inclusion of low-energy heating systems. But importantly, the performance of the home is primarily enhanced by the fabric of the building.
UK housing
In the UK, we have been on a journey towards more sustainable homes and in 2006 a ten-year target to zero carbon homes was established. Although the coalition government scrapped the Zero Carbon Policy in 2015, the political pendulum has swung back and the UK government is now committing to “world-leading levels of energy efficiency”.
To support the now legally-binding target to bring all its greenhouse gas emissions to net zero by 2050, the UK government has committed to introducing the Future Homes Standard in 2025 so that a home built to the standard will have 75% lower carbon emissions than one built to current energy efficiency requirements.
The first step towards this is a proposed uplift to the Building Regulations with very high fabric standards (typically with triple glazing and minimal heat loss from walls, ceilings and roofs) and potentially the installation of low and zero-carbon technologies.
Passivhaus - the realm of the structural engineer
One way of achieving these targets is by adopting the Passivhaus standard. Originating in Germany, Passivhaus is an example of the industry consensus that a reduction in energy consumption is delivered through high quality, thermally efficient materials and strict airtightness requirements.
But, while the number of registered Passivhaus homes is small with only 209 UK registered residential projects, the concept of enhancing building performance through design of the building fabric is becoming embedded in house building – the realm of the structural, rather than the mechanical engineer.
Structural engineers must necessarily integrate complex architectural requirements into the structure and continually innovate with new materials and products.
Despite the ‘traditional’ appearance of the homes on Goldsmith Street, the structural elements will be very different from those used in the traditional housing of the past.
Engineering innovation in house building
Outside of the conversation on Modern Methods of Construction (MMC), little attention has been paid to the ongoing and continued innovation in house design, led in part by structural engineers. Examples include:
Insulated, suspended ground floors - ground floors that are laid with a gap between the floor and the ground beneath and incorporate high levels of insulation to prevent heat loss.
Engineered timber joists - where upper floors would be traditionally built with solid timber beams, modern homes are often built using timber I-joists (similar to the shape of a steel beam) or a combination of steel and timber to form stiff but lightweight floors.
Prefabricated trussed rafters - timber roof elements that are manufactured offsite and reduce the amount of carpentry required on a construction site.
Multi-layered masonry - multiple layers of construction including thermal insulation and increasingly sophisticated components to tie them together. These are designed to be weatherproof, prevent heat transfer, provide fire resistance and resist sound transmission.
All were "Modern Methods of Construction" at one point. The design of homes, driven by regulatory change, will continue to evolve and require the specialist skills of the structural engineer.
Primary energy and embodied carbon
One final point of note is that the proposed changes to Building Regulations will, like the Passivhaus targets, use primary energy as the principal performance metric - that is the measure of energy consumption (in kWh) of a home while it is being used by the occupants.
While the operational performance of homes is important, engineers should not lose sight of the value of the assessment of embodied carbon.
It's inappropriate to use materials, systems or technologies that generate large volumes of carbon in their manufacture, transport and erection. It remains important to make design decisions that incorporate this metric.
Many structural engineers are well versed in this assessment and it would be sensible to continue to consider the embodied carbon in the design of our homes.