With the COP26 summit beginning in Glasgow this month and the latest Intergovernmental Panel on Climate Change (IPCC) report published in August, climate change is back on the news agenda.
The IPCC report presented further evidence of rising global temperatures and the likely range of future temperature increases if little or no action is taken to limit greenhouse gas emissions.
Furthermore, for the first time it reported that we’re already seeing the impacts of climate change in the form of extreme weather events, such as flash flooding and wildfires.
With buildings accounting for 17% of the UK’s greenhouse gas emissions (2019 figures), reducing the energy demand of buildings is a priority for the UK government in its attempt to make the UK net zero by 2050.
With the IPCC predicting an increased frequency of extreme weather events, climate change is also on the agenda of those responsible for our codes and standards, as they strive to ensure buildings remain safe from stronger winds, higher temperatures and potentially deeper snow.
The role of buildings in greenhouse gas emissions
Buildings contribute to the UK’s greenhouse gas emissions in two ways:
- Embodied carbon: The CO2 associated with the building fabric and its construction
- Operational carbon: The CO2 associated with the operation and use of the building
The relative importance of embodied carbon and operational carbon depends on the use of the building and its design life.
For a heated building with a 50-year life, the embodied carbon will be small compared to the total operational carbon over the 50 years, whereas for an unheated building that is demolished after only ten years, the embodied carbon will be far more significant.
Changes to building regulations over the past couple of decades (e.g. improved insulation and airtightness and more efficient lighting) have significantly reduced the operational carbon of buildings, increasing the relative importance of the embodied carbon in the process.
The embodied carbon of a building, building element or construction material may be assessed by what is known as the life cycle assessment (LCA). This takes account of all of the processes and associated CO2 from when the raw materials are extracted from the ground through to their disposal or recycling at end of life.
It should include carbon emissions associated with the materials themselves (including waste materials that are not recycled), the manufacturing processes and transportation.
For many common materials, the embodied carbon values may be obtained from established databases. Many manufacturers declare the embodied carbon of their products as part of their environmental product declaration (EPD).
The operational carbon is due to the energy needed to operate the building and includes heating (and potentially cooling), ventilation and lighting. The energy performance of buildings is already highly regulated (e.g. Part L of the Building Regulations in England) and these rules are set to become more onerous as new buildings are pushed in the direction of net zero.
The operational energy of a building, and hence the mitigation measures required to reduce its carbon footprint, will depend on building use.
For commercial buildings, reducing heat loss through the building envelope has been a priority for the past 20 years and the regulations have pushed for lower U-values (a measure of how much heat conducts through the building envelope) and airtightness.
Such concerns are irrelevant for a semi-open sided livestock shed, but there is an energy demand associated with lighting and ventilation. While the use of more efficient lighting and ventilation in this instance will reduce the operational carbon of the building, an even greater benefit can be realised by good building design to maximise the use of natural daylight and ventilation (also better for the welfare of livestock).
Design for reduced CO2 emissions
As the impact of climate change becomes more apparent so the need to tackle it will become more urgent and efforts to reduce the carbon footprint of human activity will intensify.
This started in earnest in the UK at the start of the millennium with incremental changes to building regulations to reduce operational carbon and the greater use of environmental assessments, such as BREEAM, to grade buildings in terms of their overall environmental impact.
In parallel, documents such as the ‘Green Guide’ will gather and disseminate data on the environmental impact of building elements and EPDs for construction products have become the norm.
However, with the UK government now committed to net zero, it is safe to assume that an even greater emphasis will need to be placed on the environmental design of buildings in future.
Likely changes can be grouped into three categories:
- Improved energy efficiency to reduce operational carbon
- Better use of more sustainable materials to reduce embodied carbon
- Greater incorporation of renewable energy devices
Reductions in operational carbon are likely to be achieved by continuing recent trends aimed at minimising energy wastage from inefficient lighting, mechanical plant (heating, cooling and ventilation) and heat loss through the building envelope, but the emphasis of these reductions may change.
For example, as the thickness of roof and wall insulation has increased over recent years, emphasis switched from U-values to airtightness, since proportionately more heat was now being lost through leaky joints.
This change has resulted in modern houses that are theoretically very energy efficient, but uncomfortable for the occupants, who take matters into their own hands by opening the windows in the middle of winter while the heating is on. Needless to say, there is now a greater emphasis on human behaviour and control systems.
For unheated buildings, optimising lighting and ventilation are likely to be key, i.e., allowing as much daylight in as possible without too much solar gain leading to overheating.
As operational carbon is reduced, expect a greater emphasis to be placed on the embodied carbon of the building, with sustainable sourcing and the greater use of recycled materials becoming normal practice.
There could also be a move towards structural forms that minimise material weight at the expense of fabrication effort (e.g. lightweight trusses) and construction methods that reduce waste (e.g. offsite manufacturing – which is already standard practice for frame manufacturers).
Finally, as demand for renewable electricity increases to charge all of those electric cars that we will soon be driving, it is likely that the trend to cover building roofs with photovoltaic (PV) arrays will pick up again, if the financial incentives are right. However, PVs add weight to structures and can potentially increase wind loading, so there may be implications for the design of the structure.
There are also options to harness the power of the sun to meet local energy needs, for example cladding grain stores with transpired solar collectors (steel sheets with tiny perforations) to collect hot air to dry the grain.
The consequences of climate change on buildings
One of the most shocking aspects of the recent IPCC report is that the impact of climate change is already apparent. We’ve been warned it’s going to get worse even if we slash carbon emission over the next couple of decades.
Given that all buildings have to be designed for what the Eurocodes call “climatic actions” (wind, snow and sometimes ice and thermal expansion), it should not come as a surprise if climate change results in more onerous design conditions for our buildings.
CEN (Europe’s standards organisation) is already considering how best to factor climate change into the Eurocodes, with the option of applying a scaling factor to snow and wind loads being considered.
It is also likely that the maximum temperature values used for calculating steel expansion (very important for bridges and railway track) will increase. This rise in peak temperatures will also increase the risk of buildings overheating.
Another consequence of climate change is likely to be heavier rainfall, requiring the redesign of gutters and drainage systems.
Climate change has arrived as a physical reality in the form of heat waves and storms and as a political priority. In both senses it will have consequences for the way buildings are constructed and operated.
With buildings accounting for 17% of the UK’s greenhouse gas emissions, reducing the energy demand of buildings should be a priority for our sector as we seek to limit the impact of climate change and minimise the harm to our planet.
Dr Martin Heywood
RIDBA Technical Consultant