In this blog, I write about the cost of a zero carbon house, why it’s a key part of decarbonising the economy, and what the key cost drivers are.
What is a net zero carbon house?
There are many terms used interchangeably today to describe different aspects of sustainability. Zero-carbon housing and zero-energy housing are both used to define houses with a very high energy efficiency rating. Zero-energy housing require a very low amount of energy to provide the daily needs and functions for the home
Net zero carbon homes are carbon neutral. The source of energy is via a green tariff fuel, renewable energy that balances the use of fossil fuels.
These concepts are not new. The ancient Roman architect Vitruvius advocated orienting homes to be south facing, to benefit from passive solar energy gain during the winter.
How to get to Net Zero Carbon
There are some real difficulties in getting housing stock to be net-zero, one of which is the cost. The estimator can also help by using forecasting techniques to estimate how much carbon will be saved from different solutions, and the cost trade-offs in achieving these.
You need to include the embodied carbon of materials used, the equipment used to build, the family car mileage in a year, travel abroad. Such complications mean the lifecycle cost of carbon become important, and these are coupled to the lifetime cost savings for the property from installing carbon saving technology.
Cost and carbon benefits are expected in the long term, but it means more of an upfront investment. In conventional houses you might have a standard boiler, double glazing, and generally standard building materials . A lot of equipment in a net zero house is still expensive or unusual – Mechanical Heat and ventilation equipment, special triple glazing, bespoke designs to utilise passive solar in winter, heat pumps.
In retrofitting for net zero, keep it simple. It is all about reducing the energy demand and increasing the energy efficiency of the house. The average house in the UK emits several tonnes of CO2 each year, half of which is due to space heating.
Secondary factors also include the type of clothes purchased and worn, frequency of recycling, recreational activities and use of financial and other services throughout a given year. If you have invested in bit-coin you should find out the carbon emissions required for your investment, and that should be incorporated into your carbon calculation.
Cost Drivers of Net Zero Carbon Houses
Reducing the need for space heating is the biggest reduction in carbon emissions from domestic housing. You need better Airtightness levels in combination with mechanical ventilation heat recovery systems.
What about in the the future? According to a Currie and Brown study battery storage costs have the largest expected reduction in cost relative to triple glazing, LED lighting, and other sources of air tightness and thermal bridging prevention.
New build detached or semi-detached houses have additional costs between 3% to 5% of total build costs to benefit from more energy efficient standards. These are caused by the fabric improvements and introduction of an MVHR unit. There are also additional costs of installing heat pumps, a hot water store, larger low temperature radiations and a power supply to replace the gas boiler.
Apartments are driven by the use of MVHR systems and some improvements in glazing standards. The additional cost of reducing space heat demand is smaller (at under 1.5% of capital costs) than for larger housing.
This anomalous year where supplies have been strained by the pandemic, and the notorious Suez Canal blockage, as well as an upsurge in individuals carrying out work on their own houses during the lockdown creating a supply issue.
The estimated retrofit cost is around £30,000, to achieve a standard of 15kWh/m2 of energy usage per year. This included surveys, contractors, and managing the disruption.
Including a heat pump would be around £10,000 – that’s for searches, the cost of purchasing and installing the pump, a new hot water store, and replacement radiators, some distribution pipe modifications, and repairing the walls after fitting the pump.
The lifetime operational carbon savings associated with low-carbon heat are more than double those arising from reducing space heating demand but retaining a gas boiler.
Additional maintenance costs include, after 20 years replacing the MVHR system, after 30 replacing the triple glazing, and every year replacing filters for the MHVR.
The benefits of all this work are having a low-carbon home, achieving lifetime cost savings, and protection from energy price shocks. These are significant, especially if you are on the edge of fuel poverty. There is also the increased value of the property itself relative to similar housing stock.
The challenge doesn’t seem to be how to make newer homes more efficient, it is how to deal with existing housing, our individual behaviours, and how we use our houses. And we are all becoming a lot more conscious about the sustainability of our choices.
It is not possible to estimate the cost for every type of house in every scenario accurately. There are still questions about what zero carbon actually means. Carbon neutrality needs to be audited and quantified. Critical to sustainability built homes is their long life and low energy use, as these are factors that will reduce life cycle costs.
A combination of activities will be required by stakeholders to enable low carbon housing to be developed at scale, and to retrofit the existing housing stock in the UK. Solutions could include more stringent building standards, managing peak energy demand through more efficient usage, our own individual habits, and carbon taxes.
For more on cost analysis for net zero carbon, The Zero Carbon Hub have great resources to understand techniques, trends and costs.
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