Charlie Luxton
Charlie Luxton: Fundamentals of Energy Efficiency
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Charlie Luxton: Fundamentals of Energy Efficiency

60 per cent of the energy used in an average house goes on space heating so this is the issue you need to focus on first and foremost.

Since I started designing houses 15 years ago, interest in energy efficiency has grown and has become a big thing for many of my clients. The reason for this increased attention has been driven by bigger, often quite abstract, issues like climate change and the nation’s health. Given that more than 27% of CO2 produced by this country comes from our homes, reducing this for the sake of our climate is clearly a priority.

Model home external

As the cost of fuel rises, it’s key to the nation’s health and happiness to ensure that we can all affordably warm our homes. Spending more now to make houses cheaper to heat in the long run will bring large savings. However, when working on a building project, balancing long and short-term benefits is not something we always manage successfully and finding funding to drive down energy consumption often drops down the priority list. So, whilst these reasons are compelling, they are undoubtedly a little hard to grasp or justify in the cut and thrust of a building project.

CLH bedroom When working with a new client I always try to argue the reasons for embracing sustainable homes, and the reason I push the hardest is a very simple and compelling one. Living in a house that is not losing heat, that is super insulated and airtight and has no drafts or cold-spots, is pure and utter luxury. Still, calm, quiet; they are almost unnervingly comfortable. Once you’ve experienced the comfort of low-energy living you will never want to live in a normal, cold, draughty house again. Super sleek German kitchens and hi-tec surround-sound cinemas might be the luxuries of today, but low energy homes are the ‘must have’ of tomorrow. Saving the planet, saving money and enjoying absolute luxury – what’s not to love?

By now, I hope you are all revved up and wanting to get a bit of this energy efficiency going… but what to do? It is a fast moving, complicated, confusing area and every project is unique, but here are some guiding principles to focus on for both new builds and refurbishments.

60 per cent of the energy used in an average house goes on space heating so this is the issue you need to focus on first and foremost. The best way to achieve this is through a fabric first approach. Focus on reducing heat loss through insulation, good windows and airtightness rather than focusing, as many do, on how to heat the house through low carbon technologies, such as Heat Pumps, Photo Voltaic panels or Bio-mass boilers. Put simply: reduce heat demand as much as possible before you work out how to heat. I am amazed at how often people focus on low carbon technology, how to generate heat/energy rather than trying to save it. To me, it’s the equivalent of having a puncture and obsessing about what pump to buy rather fixing the puncture.

 It is a case of insulating as much as possible… and then some more!

Insulation is the starting point. We are not talking about a few tatty layers of fibreglass in your loft; we are talking a minimum of 300mm up there, properly installed. It is a case of insulating as much as possible… and then some more! In existing buildings, I often recommend digging out the floors to get at least 200mm of polystyrene under your feet. We’re working on a low energy new build house at the moment and the entire building is sitting on a 300mm insulation raft, so nothing touches the cold ground.

A little surprisingly perhaps, your walls are most likely to be your biggest source of heat loss. Fill cavities where suitable and think about additional external or internal insulation. In our projects, we try to aim for a minimum of 200mm insulation in any wall.

CLH downstairs internal

The key is not only to have plenty of insulation but to make sure it’s done properly. There should be no gaps anywhere, not only do gaps make you lose heat but they also allow moisture to condensate on the resultant cold spots. This often leads to mould – a big health risk – so you have to be very careful to ensure it is installed properly.

Another tip is never skimp on windows; they are a key part of your insulation and are changed very infrequently.  A house will go through at least 4 boilers before windows need replacing, so getting them right at the beginning of a project is critical. It’s important to think about glazing options, whether you’re working on a new building project or an existing one.. Existing houses should have at least double-glazing. Make sure they are fitted properly; air leakage around windows is a big problem – roof lights should also be considered in the same way.

After insulation and windows, good airtightness is vital. Increasingly, the effect that drafts and air movement within the dwelling have on energy consumption is being understood. With still air in your house 19°C is the perfect internal temperature for most people. As soon as there are draughts 21°C is required, and you will still get cold spots, which will have a big impact on your comfort and energy bills. You need to seal up the entire building; which isn’t easy in a new build, and very hard in an existing house, but critical to a comfortable home. Skirting boards, through the floors and sockets, around windows, down chimneys, you name it, draughts will find a way in. Your house is probably as leaky as a sieve, so go round with tapes, membranes, silicon, mastic, chimney balloons – anything to stop air movement.


If there is one thing that you need to keep in mind it is that low-energy, comfortable homes are carefully devised and extremely well-built. Make no mistake, whether new build or refurbished, low energy homes are not easy to achieve but once you do, you’ll never go back!


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