10 Principles of ‘Green’ Home Design
Charlie Luxton, spokesperson for The National Homebuilding & Renovating Show, 22-25 March 2018, NEC, Birmingham (www.homebuildingshow.co.uk), says:
For most people the driving reason behind building a low energy home is about saving energy and therefore money. Undoubtedly the whole abstract idea of saving the planet comes into it but the reality is that it comes down to low bills. I have no issue with this whatsoever…well almost….
My design work is focused on housing. New builds, extensions, refurbishments all driven by a desire to be as sustainable as client, brief and budget will allow. Through this I’ve come to believe that the reason the take up for sustainable building techniques is so low is precisely because the debate has concentrated on money saving and of course payback for too long. I believe this is the wrong issue to focus on. Over the last few years I have evolved my sales pitch so that when I am trying to persuade someone to invest significant amounts of money in air tightness and super high levels of insulation, triple glazing, MVHR I no longer focus on the lower bills but on the quality of space.
It is a wonderful by-product that low energy spaces properly built are far nicer places to live. Still, calm, healthier and quiet they are almost unnervingly comfortable. Once you’ve experienced low energy housing you will never want to live in a draughty and cold old school home again.
More comfortable, better for you, lower bills and doing your bit to conserve a habitable planet, it sounds too good to be true. The only down side is that while cheaper in the medium to long term, low energy construction costs more up front. It is also fast moving, constantly evolving area with a lot to understand and keep up with. There are however some simple principles that guide me through the mine field of sustainable design.
1.SMART DESIGN – One of the best things to come out of the whole sector is thermal modelling. This is the ability to use computer programmes to test the energy, thermal and water performance of a design as it evolves. This allows designers to optimise a buildings shape, orientation, windows and insulation to passively use the sun to do as much heating and lighting as possible. It goes hand in hand with a fabric first approach, 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; Heat Pumps, Photo Voltaic panels or Bio-mass boilers. I would never design a new house without using thermal modelling to inform the process.
- BEWARE OVER HEATING – All these large south-facing windows and lots of insulation are wonderful but many new builds are suffering for over heating. With our climate set to warm considerable over the next 50 years this is only going to get worse. One of the main reasons for thermal modelling is to test for possible overheating and design it out at an early stage.
- SIZE – We calculate energy consumption through kW/m2/Annum. The bigger the house the bigger the bills so try to make space work harder for you rather than just making more space. Small can be beautiful and allows you to spend more money per m2 to get better quality.
- INSULATION – It certainly isn’t sexy but to make super comfortable low energy homes insulation is your biggest asset. Critically, 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!
- NO COLD BRIDGES – The key to insulation is just lots of it but it must also have totally continuity. Any gaps or bits of structure; lintels, masonry, timber that bridge the insulation layer not only loose heat but moisture condensates on the resultant cold spots. This often leading to mould, a big health risk, so you have to be very careful your insulation layer is carefully designed.
- WINDOWS – Windows are important to get right especially as they are replaced so infrequently. A house will usually go through multiple boilers before the windows are replacing, triple glazing for new builds and at least double-glazing for existing homes. It is not just the quality of the windows, how they are fitted is equally important. Air leakage around windows is a big problem and using the right foams, tapes and fixings is critical.
- AIR TIGHTNESS – After insulation airtightness is vital. This means sealing up all the gaps and holes in your buildings. Drafts and air movement within a dwelling has a huge impact on the comfort of a home. 19C is the perfect internal temperature for most people in a well-sealed free house but if there are draughts 21.C is required. This seemingly small rise in temperature will have a big impact on your comfort and energy bills.
- MECHANICAL VENTILATION HEAT RECOVERY (MVHR) – Once you’ve highly insulated and sealed a house the biggest source of heat loss is ventilation. People need lots of fresh air to be healthy to provide this and maintain airtightness you need MVHR. This is a system that extracts warm moist air from bathrooms, kitchens, utilities and passing it through a heat exchanger to pre-heat fresh air form the outside which is pumped into the bedrooms, sitting rooms etc. It provides up around 4 times the ventilation rates in a normal home and filters the air for dust, pollen and pollutants. In a well-insulated airtight house it will halve energy consumption and give fresh warmed clean air. I think it is one of the best bits of technology to come into the low energy sector.
- INTERNAL AIR QUALITY – In terms of creating low energy comfortable but also healthy homes making good internal air quality is central. MVHR helps by upping the ventilation rates, reducing moisture and filtering air that comes into the house. I am always very careful to try and specify low toxicity and low off-gassing materials. My rule of thumb is that if I would eat my dinner off it, I will put it in a house! Think about reducing the use of MDF, particleboard and petroleum-based products.
- DON’T LOSE THE JOY – It is easy with all the additional complexity of all these issues to lose sight of the fact that your house should be joyful and inspiring. Sometimes low energy architecture can become a little too worthy and rational. You need a bit of magic and spark in a project, don’t let low energy concerns kill that.
Whether new build or refurbished, low energy homes are not easy to achieve but once you do, you’ll never go back. 50 grand super sleek kitchens and surround sound AV rooms are the luxuries of today, low energy homes are the luxury of tomorrow.