26.09.2019 : Timothy Howarth

Density and decarbonisation - the future of buildings

As a global community – governments, business, industry, communities... all of us – we have just over 30 years to work together to avert catastrophic global heating by reducing our carbon emissions to zero by 2050. Within 10 years we all need to drastically bend the emissions curve to hold global temperature rise to within 1.5°C of preindustrial levels and avoid a potentially dangerous tipping point. That’s not to say there has not been a lot of hard work already completed – but we need to step up the level of urgency and focus on this important issue. 

In terms of the climate crisis and building and construction – what does the future hold? And what will the buildings of tomorrow need to look like? 

Decarbonisation is ultimately far cheaper and easier the earlier we start, than delaying and dealing with the consequences at the other end. Let’s not forget that the Stern review's main conclusion presented to the Government of the United Kingdom in 2006 was that the benefits of strong, early action on climate change far outweigh the costs of not acting or acting too slowly or too late. 

To look forward, we first need to look back. It’s exasperating to think that we’ve had the tools and understanding to reduce energy consumption and significantly decarbonise our building stock for at least the last 40 - 50 years.  The 1970s oil crisis triggered much of the early research and building science developed in this space, and the solution identified was energy efficiency. Working hand in hand with densification, you can significantly reduce embodied and operational energy related carbon emissions from buildings. 

Density is essential for compact, efficient, walkable, cyclable and safe cities. Urban sprawl benefits no-one - To get an idea of the cost of urban sprawl, take a look at the city of Winnipeg.  The land area occupied by Winnipeg has increased 100% since the 1970s yet the population has only increased by around 40%. This means that the rates paid by every homeowner today must support 40% more infrastructure and city services than they did 50 years ago.  And we wonder why our rates keep going up? 

With density, communities are going to need to consider buildings with compact footprints and be smart in how they address orientation, height, set back and access to daylight amongst many other considerations. A compact building form or the heat loss form factor is a great segway into energy efficiency.  

Much in the same way that penguins can huddle together and share their warmth, so can we. A detached dwelling usually has a surface area to volume ratio of between 3 and 4, while a small three level apartment building might have a ratio of around 0.5, and a high rise building 0.2.  The zoning density and therefore the size and shape of a building, with all things being equal, can reduce the heat loss or gain of a building anywhere between 5 and 20-fold. The materials and embodied carbon used in the construction of the same building also follow a similar pattern of efficiency, dependent on the types of materials selected and used. 

Once the building location, shape and form have been established, the next area of focus should be the energy efficiency of that building. This is where a lot of the early research in the 1970s occurred and more recently crystallised as the Passivhaus Standard in the early 1990s. The passive elements of a building such as the building envelope including the insulation, (elimination of) thermal bridges, air tightness, window performance and external shading can reduce heating and, to an extent cooling demand by as much as 90% from building code minimum.   

At this level of efficiency, it’s almost possible to heat these buildings passively using the internal gains of the building occupants and free solar gain, with very little additional input.  The passive elements of a building last 50 or more years and shouldn’t need replacing, which makes for a very effective whole of life cycle cost too.  

After the passive elements of a building are addressed, attention needs to be given to the energy efficiency of the active systems such as the building services which provide the heating, ventilation and air conditioning. These services, designed efficiently, can reduce a building’s energy consumption by as much as 30% or more when compared to the building code minimum.   

For example, if you replace fossil fuel boilers in buildings with heat pumps, and electrify the heating and domestic hot water systems, it’s possible to reduce the carbon emissions from natural gas combustion six-fold. 

Finally, the operational energy consumption, typically the largest contributor towards the carbon emissions in a building’s lifecycle, needs to be managed efficiently through continuous commissioning and building tuning.  In new and existing buildings this can reduce building energy consumption and carbon emissions anywhere from 10 – 30% and sometimes more. 

So, the answer is simple - the future of buildings is to look to our past and leverage what we’ve already learnt.  To minimise energy consumption and carbon emissions from buildings, they will need to have a compact form factor; they will need to leverage the passive elements of the building envelope to significantly reduce heating and cooling demand on the building services; and the combustion of fossil fuels from the operational energy of a building’s lifecycle will need to be eliminated.  

Three easy wins for decarbonising buildings! 

About the Author

Timothy Howarth

Environmentally Sustainable Design (ESD) Engineer

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