6 Steps to an Energy Efficient Home

We’ve all now heard the term ‘zero-carbon home’. In late 2006, it became Government policy to build all new homes to this standard by 2016 (2011 in Wales). Whilst some might argue that this is too long to wait, others strike a note of caution and point out just how tough it will be to cajole a reluctant building industry into a 21st century agenda.

Attention for many people focuses on renewable technologies, but these are arguably just the icing on the cake. The energy-efficient filling involves taking a close look at how we actually build houses, and how we can build them better. There are a few key points that come up time and again.

1: INSULATION

We are still not using enough. The requirements for insulation have been tightened no less than six times since they were first introduced in 1976, but we are still nowhere near the thicknesses used in Scandinavian homes, which is what is required if we are to reduce heat loss to a bare minimum. One of the problems is that we mostly build homes with masonry cavity walls, and it’s difficult (though not impossible) to increase the widths of the cavities to the levels required. However, Bill Dunster’s BedZed development (not to mention thousands of German passive houses, or ‘PassivHaus’) has shown that you can pack 300mm of insulation into a cavity wall construction and not suffer any unexpected consequences — so it looks as though there is a way forward for masonry construction in the brave new world of zero-carbon developments. It’s just that, at the moment, such a level of insulation is still exceptionally rare, and traditional bricklayers won’t have a clue how to go about building a cavity this wide.

The alternative approach is to look for different construction systems that promise much lower U-values. Timber frame is the best-known one, but even here the standard UK timber frame wall, at 140mm thickness, is still someway light of what is required for an ultra-low-energy home. Timber frame can, however, be fairly easily adapted to greater width demands. Other build methods, such as SIPs and ICF (both popular with selfbuilders), offer potential routes to getting ultralow- energy structures; but, in truth, all of the options currently being marketed in the UK are somewhat short of the standards that are going to be required by 2016.

2: AIRTIGHTNESS

Traditionally, British builders haven’t given a moment’s thought to draughtproofing 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 standard, require that houses are pressure tested on completion and that the homes should meet very stringent levels of airtightness. In 2006, the England and Wales Building Regulations introduced a requirement for air pressure testing for the first time, but the bar was set at a very low level. In fact, all but the very worst examples will easily pass the new test. The German PassivHaus standard is over ten times more demanding.

To get an airtight house, you have to pay close attention to the detailing and the junctions, and avoid any unnecessary penetrations. Both masonry and framed constructions are capable of getting good air pressure test results, but some techniques perform very poorly. Unfortunately for UK builders, this includes the popular practice of sticking plasterboard onto masonry walls (known as dot and dab), rather than applying a wet plastered finish.

3: GOOD VENTILATION

Having gone to all this trouble to seal the house from unwanted drafts (thus losing valuable heat), you then have to pay close attention to 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.

4: 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 truth, passive solar design isn’t critical in the UK climate: it works best in spring and autumn.

5: COOLING

In Mediterranean climates, cooling houses in summer uses more energy than heating them in winter. Whether or not our climate trends this way, 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.

6: HEATING SYSTEMS

Many people start out with the hope that if they build an ultra-lowenergy 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 woodburning stove makes a great central focus for any house.

Further reading:

• How to Specify your Eco Home
• A Complete Guide to Heating & Plumbing for Your Self Build
• The Path to Zero Carbon