Space heating accounts for 50 percent of the space heating demand for a house (it therefore accounts for roughly 50% of the carbon emissions and the fuel bills.) Historically studies have shown that if you under optimise energy efficiency then actual savings are much less significant that one would tend to expect. Why should this be the case? There are a number of factors some of which are technical and others are behavioural. I will discuss these issues below.
The economic and behavioural issues that prevent carbon emissions savings being made are relatively straight forward. If we consider an existing uninsulated home that is costly to heat, let say that the bills are more than 10 percent of the household income, then the energy use is not so much limited by the desire to be warm but by the available money to spend upon heating. A family that lives in social housing may, as a result of a government incentive, have their home refurbished by their landlord. To date, as the occupant has not had to pay for the retrofit, they have quite naturally sought more affordable warmth. By this I mean that they have still spent 10 percent of household income upon fuel but they have benefited from a warmer, more comfortable home. As the fuel use has not actually declined there have been no carbon emissions savings.
For the owner occupier that has to absorb both the fuel costs and the retrofit cost there is less opportunity for increasing the affordable warmth. So in this case energy bills and carbon emissions should be reduced but the average room temperature will not increase and as a consequence standards of comfort will not be improved unless more money is spent upon heating.
For the social housing example it is interest to note that because the insulation is being made to "work harder" (resist more heat loss) than would otherwise be the case the payback on the insulation if far faster than for the owner occupier. But one must ask whether payback really a useful term. It is fair to say that in the insulated wall with the most immediate payback has about 25mm or so, but what is less appreciated is that, all things being equal, the lifecycle cost for 400mm is approximately the same, even though the payback is somewhat extended ! Why is this? Put simply it is because the ongoing fuel bills trade off against the cost of the lifecycle benefit of the insulation. If we stick to simplistic concepts such as "payback" then we are at risk of missing out on the big picture.
So if we are serious about reducing carbon emissions and energy use, and perhaps more importantly improving health, well-being and thermal comfort then we need to start thinking differently. Walls with thick blankets of insulation would start to become the norm and it is here that skills in design and construction come to the fore. As energy efficiency standards increase skills levels also need to improve. There is no point installing 300mm of insulation badly! If this happens then most of the theoretical savings will not be delivered in practice. As insulation standards increase thermal bridging and air gaps and poor draft proofing start to play an increasingly important role. These commonly overlooked issues can significantly undermine performance considerably.
So what kinds of performance can be achieved? I have recently worked upon three award winning retrofit schemes that have the ambition of reducing carbon emissions by 80 percent. The energy demand is also reduced by a similar proportion. In principle to achieve our goal we used superinsulation, draftproofing and ventilation heat recovery. We also used energy efficient lighting and appliances. As the projects are still being monitored and as a consequence it is not yet possible to verify whether the desired performance has been delivered, however, as Passivhaus standards of quality assurance have been employed we remain hopeful.
Studies of standard practice in the UK have shown energy consumption being 50-70 percent higher than intended. This has lead Dr Jez Wingfield from Leeds Metropolitan University to say "Until we have a robust means of checking and verifying performance the targets themselves become secondary." Quality assurance therefore plays a key role in achieving reduced energy bills, reduced carbon emissions and improved health and happiness. The UK Accreditation Service has been employed to keep and on the quality assurance for the Green Deal. This is certainly a good thing but one must question the experience of the organisations ability to deliver measured reductions in carbon emissions. I have not found any data suggest that it has any at this time and as a consequence we have looked for reliable alternatives. This has lead to us compiling a review of over 250 Passivhaus homes. It was found that on average they have performed as intended. In essence this would appear to demonstrate that the quality assurance tools and methods developed by the Passivhaus Institute have been repeatedly shown to deliver the standards of performance that are required by ultra low energy buildings.
It is also interesting to note that British Gas are currently developing the "Home Energy Plan". This is in effect another Green Deal. Interest rates for this scheme will be set at 6.9 percent, unfortunately research published last year by the Great British Refub campaign suggested only 7 per cent of the public would be 'likely' or 'fairly likely' to take advantage of the green deal if interest rates were set at 6 percent. The Department of Energy and Climate Change tells us that over all these measures will lead to a rise in dual fuel bills of 7 percent.
Does anyone see the issue? If the UK Government creates a green fund that enables interest free loans that simply track inflation then the uptake could be considerably higher. The capital expenditure would also stimulate the UK's frail construction industry. At face value this could be achieved at zero cost to the nation, however, if we consider that the manufacturing industry could also get on board then the UK could become a net exporter of retrofit technologies.
So what can we learn from this discussion? Do it once and do it right. Compromise is not an option; rather we should be prepared to think in terms of optimising buildings for minimised energy demand, improve comfort and ideally vastly reduced carbon emissions. The biggest risk is that the per-property budget for the Green Deal will only pay for flimsy standards of energy efficiency and as a consequence will fail to achieve its potential. Bolder performance standards and lending mechanisms will be required if the Governments own legally binding target of achieving a 50 percent reduction in carbon emissions is to be achieved by 2025.
NOTE: This article was originally written when author worked at DEWJO’C Architects (which latterly became Devereux Architects). In 2011 Mark set up his own practice so that he could continue to pursue his interests in developing sustainable, low energy architecture.
Notes on the author:
Mark Siddall, principle at low energy architectural practice LEAP, is an architect and energy consultant specialising in low energy and PassivHaus design. He was project architect for the Racecourse Passivhaus scheme and has a keen interest building performance. In addition to architectural services his practice provides project enabling and education for clients, design teams and constructors.
LEAP website: www.leap4.it