In the last part of our three-part series aimed at helping you make your home more environmentally friendly, we’ve teamed up with Home Building & Renovating Magazine to look at how self-builders can make new properties greener.
Many self-builders focus on renewable technologies that will be used in their new properties.
But just as important is how we actually build houses, and how we can construct them to be as energy-efficient as possible.
It’s all very well to think about eco homes in terms of the sexier features such as heat pumps and solar panels, but the crucial starting point is to ensure that the heat your home generates doesn’t escape.
Providing the best possible insulation really is about the most environmentally friendly thing you can do to a new or old home.
You have to build a structure that is insulated beyond the requirements of current UK building regulations. This generally calls for the adoption of non-standard techniques because mainstream building methods struggle to cope with walls and roofs that contain 300mm or more of insulation.
It is difficult (though not impossible) to increase the widths of traditional masonry cavity walls to the levels required. Timber frame, SIPs (Structural Insulated Panels) and ICF (Insulated Concrete Formwork) however, are better ways of getting ultra low-energy structures.
Next, think about airtightness. There is no point building a well-insulated structure if you then let all the heat leak out. Traditionally, British builders haven’t given a moment’s thought to draught-proofing houses, other than fitting draught strip around the doors and windows.
But the low-energy housing standards that we are being encouraged to follow, notably Germany’s PassivHaus (passive house) standard, require that houses are pressure tested on completion and that the homes should meet very stringent levels of airtightness.
To get an airtight house, you have to pay close attention to the detailing and the junctions, and avoid any unnecessary penetrations.
Having gone to all this trouble to seal the house from unwanted drafts (thus losing valuable heat), you must also think about providing good ventilation so that indoor air quality doesn’t suffer. Most of the low-energy homes around the world use mechanical ventilation systems, with added heat recovery, so that any heat losses are minimised.
Passive solar design
If your site allows it, it is preferable to make use of a south-facing aspect to let winter sunshine heat up your home, a theory known as passive solar design. It works best where you have an internal heat store, such as a tiled floor or a brick chimney, which gets exposed to direct sunlight. However, care should be taken not to overglaze the southerly aspect, as this can cause problems with overheating.
In Mediterranean climates, cooling houses in summer uses more energy than heating them in winter. Whether or not the British climate becomes more like this, it would be remiss not to pay attention to the issue of cooling. In fact, good insulation and airtightness levels help a great deal in this respect, as the heat of the midday sun is largely kept out of the house. The best designs use some form of shading to keep the summer sun off the glazing.
Many people start out with the hope that if they build an ultra-low energy house they will be able to dispense with a heating system altogether. However, such an approach can be problematic.
Even if the space-heating demand is minuscule, there will be times when the house will not be comfortable without some form of heating. And there is always going to be a need for domestic hot water which can’t be met entirely by solar panels. Rather than fitting a full heating system, many of the German passive houses add a small heating unit onto their ventilation systems. Alternatively, a wood-burning stove makes a great central focus for any house.
For more information visit www.homebuilding.co.uk/green