The path to net zero: how our built environment is set to be transformed

In its latest report, the Committee on Climate Change (CCC) has encouraged the government to use the country’s recovery from covid-19 to accelerate the transition towards a net zero carbon economy. The construction industry is likely to be at the forefront of these efforts, with changes to Part L of the Building Regulations (which governs energy performance) for new homes in England and Wales set to be published before the end of the year and consultations on changes for all other buildings expected to open soon. This move will bring both challenges and opportunities for the industry, and to properly prepare, it is important to have a clear vision of what net zero buildings will look like.

Decarbonising supply

One key aspect of the net zero transformation will be the move from traditional gas and oil heating systems to decarbonised sources. This will include increased electrification, through the use of technologies such as heat pumps supported with onsite renewable generation, along with the use of district heating schemes on larger projects.

The Scottish government has stated that all new homes will need to use renewable or low-carbon heating systems from 2024, with these systems also phased in for non-domestic buildings at the same time. Similar changes are expected as part of the revisions to Part L in England and Wales in 2025.

Any move to decarbonise supply must be matched with work to significantly limit energy demand

This move presents some clear obstacles. Heat pump technologies currently come at a premium, and the long-term cost of electrical supply is significantly higher than for gas. Care must therefore be taken to ensure building owners can afford to heat their properties effectively.

There is also an issue of seasonality. During the winter months, when demand is at its highest, the cooler temperatures, lower sun angle and shorter days reduce the effectiveness of air-source heat pumps and photovoltaics. This could place considerable strain on the national grid, particularly as we move to electrified vehicles, potentially raising carbon emissions.

As such, any move to decarbonise supply must be matched with work to significantly limit energy demand.

Fabric first

The CCC estimates that space heating demand for a typical net zero home should be within the range 15-20 kWh/m²/yr – a significant reduction on the current UK average estimated at 130-140 kWh/m²/yr.

To reach this, properties will need to achieve excellent levels of thermal performance. A good indication of the U-values they will be expected to meet is provided within the notional dwelling targets in the recent Welsh Part L consultation (shown in table 1). These demanding targets will place greater emphasis on the thermal conductivity (lambda value) of materials as use of lower performing insulation materials (those with higher thermal conductivity values) may significantly increase construction depths compared with those built to current standards.

Table 1: Proposed U-values for both notional dDwelling options within Welsh Part L domestic consultation

There will also be a greater emphasis on accuracy of design and installation around details to prevent thermal bridges, and tougher airtightness targets with clean air supplied through mechanical ventilation heat recovery systems. This focus on detailing and airtightness is likely to see increased adoption of offsite solutions, such as structural and steel-faced insulated panels, which combine precise fabrication and excellent out-of-the-box fabric performance with a fast-track build programme. 

It is likely that measures implemented on new and existing buildings will be expected to be recorded within a digital passport along with monitoring data of the actual building performance

All measures should be designed using a whole-building approach to ensure they function effectively. This is particularly crucial for existing buildings, where the unique characteristics of the property need to be taken into account. PAS 2035 provides a clear framework for how energy improvements can be delivered on domestic retrofit projects while avoiding potential unintended consequences.

It is likely that measures implemented on new and existing buildings will be expected to be recorded within a digital passport along with monitoring data of the actual building performance. This monitoring is seen as key to upholding standards and closing the performance gap.

By adopting this approach, it should be possible to minimise the building’s emissions. Any remaining demand will then need to be met through a recognised offsetting scheme.

Meeting the challenge

The move towards net zero carbon building will require significant upskilling with the construction industry. By meeting this head on and looking to implement best practice now, firms can place themselves well for future opportunities whilst ensuring their buildings form part of the solution to this global effort.