Put simply, an energy efficient home is one that requires a small amount of energy to run. Homes in the UK are responsible for 21% of our overall carbon emissions[i], therefore it is imperative we improve the efficiency of our existing housing stock and build highly efficient new builds if the UK is to meet its carbon targets and reduce the impact of climate change. A more efficient house requires less energy to heat and power, which will reduce your carbon footprint by reducing the amount of fossil fuel-based energy required to run it. In fact, by retrofitting your home can reduce its energy consumption by 60-80%[ii]. This has the added benefit of reduced energy bills, therefore having an energy efficient home has benefits for you and for the environment – helping to cut your costs and leaving a healthier planet for future generations.
There are different ways to achieve this, and some key terms that it is important to understand if you are thinking about making your home more energy efficient or about buying an energy efficient house. Think of the following as your eco-retrofit glossary!
- Fabric First:
This is the idea that when designing an energy efficient building it is important to improve the performance of the thermal envelope before considering “bolt-ons” such as renewables or technology. This is a sensible approach because if you have good insulation in the walls, floors and roofs it means that the building itself will have a lower energy demand and any technology installed subsequently will require less energy to run.
- Passive Design:
Passive design principles involve using the natural environmental conditions to reduce the energy demand of a building. Examples of it include maximising daylight to light rooms rather than requiring more artificial lighting, capturing solar gain to heat spaces to reduce heating demand and designing openings so that buildings can be cross ventilated to reduce requirements for cooling.
- Net Zero Carbon:
Net zero carbon buildings are buildings that contribute no additional carbon to the environment. There are two uses of the phrase net zero when it comes to construction:
Operational net zero: operational net zero carbon means that a building generates no additional carbon in its use. This could mean that it generates the same amount or more energy through renewables than it uses in the course of a year, or that the energy it uses is generated by renewables off site.
Net zero construction: a building that is net zero in construction means that it contributes no additional carbon to the environment through the materials used and the process of constructing the building. Materials have embodied carbon (see below), this refers to the carbon generated in the manufacturing and transport of the material. The construction process also generates carbon, through delivery of materials to building sites and the energy used in the building process. Different materials have higher or lower embodied carbon, for example in general concrete has a high amount of embodied carbon and timber has a low amount of embodied carbon. To achieve net zero construction the carbon generated through the construction of the building needs to be offset, either through increased renewable energy generation onsite throughout the lifespan of the building, or by carbon offsetting, generally through paying for carbon credits in a carbon offsetting scheme.
Embodied Carbon: when thinking about embodied carbon it is important to think about the lifespan of the building, how it will be disassembled, and what will happen to the materials after demolition. If a building is constructed, demolished and replaced after 30 years then the embodied carbon needs to be offset much quicker to achieve net zero construction than if that same building is demolished after 60 years, or 300 years etc. It is important to think about what will happen to the materials used to construct a building after it is demolished – can they be recycled and made into another product, or even better, re-used? If buildings are designed to be disassembled so the materials can be re-used to build new buildings, then the embodied carbon within the materials can stay locked up in them for longer.
It is generally simpler to achieve operational net zero rather than net zero construction, by building highly insulated, airtight, efficient buildings with low carbon heating systems and renewable energy generation on site or locally. However, to build in a genuinely sustainable way, it is important to think about reducing the embodied energy of materials used, and about the lifespan of buildings and reducing waste in construction.
- Passive House:
Passive House is a building standard which has strict performance criteria for buildings including limits on heating demand, energy demand and airtightness. A Passive House has to be designed by a Passive House Designer/Consultant who will model the building in the design process to understand its energy performance, and the construction has to be certified by a Passive House Certifier to verify that it performs according to the design. There is a Passive House standard for retrofit projects called Enerphit, which has slightly less demanding criteria than the new-build standard.
- Energy Performance Certificate:
The first step in understanding the energy efficiency of your home is to look at its Energy Performance Certificate (EPC). You can find your house’s EPC online if you don’t have a copy of it at https://www.gov.uk/find-energy-certificate . If your house does not have an EPC then getting one done is helpful in understanding how your house is currently performing. The EPC gives a property an energy efficiency rating of A – G, where an A-rated house is very efficient and a G-rated house is very inefficient. It also gives tailored recommendations on how to improve the rating, with a breakdown of the improvements in rating that could be achieved with these measures.
- Decarbonisation:
Decarbonising our housing stock involves removing fossil fuel based heating systems, using electricity generated from renewable sources and reducing the overall energy demand of our housing. The Government are proposing to implement the Future Homes Standard from 2025 which would mandate that all new build homes from that date will be “zero-carbon ready”. This means that they would not require retrofitting to be zero-carbon in operation once the electricity grid is further decarbonised. This will be achieved through high levels of building fabric efficiency and the use of low-carbon heating technologies[iii]. The government plans to phase out the installation of fossil-fuel based heating systems (e.g. gas boilers) so they won’t be allowed to be installed in new-build houses from 2025[iv].
- Airtightness:
Airtightness means the control of unwanted air leakage through the fabric of the building. In new build houses the building regulations specify a maximum level of allowable air leakage. In Passive House buildings the airtightness standard is even stricter. The more airtight a building is, the less air can escape through the construction. Increased airtightness can help to reduce energy bills as less warm air leaks out of the building.
- U-value:
The U-value describes the thermal transmittance of a material or a build-up of materials. This is the rate of transfer of heat through a structure divided by the temperature difference across it. The units are W/m2K. If a building element has a low U-value, this means heat transmits through it slowly. Therefore, a building element with a lower U-value is better insulated than a building element with a higher U-value.
Although some of the calculations and properties involved in improving the energy efficiency of a building are complicated the principles are simple. They include working with the natural opportunities of the site and the climate, insulating structures well ensuring continuity of insulation around the whole of the building envelope, reducing and, if possible, completely removing the use of fossil fuels in generating heat and power for the building, reducing waste, and finally, considering the types of materials used, how long they will last and whether they can be recycled after use.
At Keystone Architecture and Design we are passionate about improving the sustainability of the built environment. We have the knowledge and skills to take a holistic approach to designing your new building or extension, ensuring you get a high-performance building with the spaces you need and the finish quality you want. If you are considering an energy efficient new build, a Passive House project or retrofitting an existing property please contact us to see how we can help by email, phone or by using the contact form on our website.
07752 979244
www.keystonead.co.uk/contact
[i]https://assets.publishing.service.gov.uk/media/60114c6c8fa8f565494239a7/Government_response_to_Future_Homes_Standard_consultation.pdf
[ii]https://www.britishgas.co.uk/the-source/greener-living/gas-boilers-ban-2025.html
[iii]https://energysavingtrust.org.uk/why-we-must-act-now-to-transform-inefficient-homes/
[iv]https://www.ecomerchant.co.uk/news/12-ways-to-reduce-embodied-carbon-in-refurbishment-and-retrofit-projects/#:~:text=Good%20retrofit%20for%20existing%20homes,carbon%20or%20renewable%20heat%20generation.