The Government has seriously miscalculated the cost of green homes

Sustainable refurbishment
There's a lot of nonsense talked, bought and done when it comes to eco-retrofitting houses. David Thorpe's new book sorts the wheat from the chaff, and challenges some green orthodoxies...

Our homes are responsible for 60 per cent of EU building energy use, and around 80 per cent of the homes we will inhabit in 2050 are here now. So if we're to meet the target of reducing carbon emissions by 80 per cent by 2050, it's vital to find out what measures work to achieve this in existing homes.

We know that retrofitting insulation and glazing can easily reduce heating/cooling energy use by 30 per cent in many buildings. With more effort, savings up to 80 per cent can be achieved. But the problem is that the building industry has never had to monitor its constructions to see how effective they are.

What we do know is that, of the environmental renovations that have been evaluated, on average they perform thermally only half as well as predicted. This could be because of bad installation, people turning the heat up, or failure of the materials.

Government thinking is far from clear on home renovation. It is using carbon cost-effectiveness as a way of estimating the net cost per tonne of CO2 reduction resulting from various policies. But try as I might by trawling through their documents, I can find no reference to the standards aimed at for the different insulation measures that are used as the basis for their calculations.

Such standards might be the projected U-value of the home or measure, or the air changes in the dwelling per hour, or the absolute final energy use. If we are unclear of the baseline we're starting from and the success of the measures then a figure like '40 per cent reduction' of CO2 emissions is meaningless.

How much will it cost?

The Coalition's New Green Deal aims to repay the cost of renovation from the resulting energy savings. A figure of around £6,800 per home has been mentioned. But is that sufficient to tackle all the necessary modifications? Neil Morgan, the director of Retrofit for the Future, a project tasked with trying to find out what does work, thinks that to achieve 80 per cent reductions on average will require around £60-70,000 per property. That is ten times more.

But what if we alter the method of calculating the benefit of thermal insulation? This is usually judged using a simple financial payback calculation, but the relationship is not a linear one - once a certain insulation standard is achieved, lifetime costs jump down as a central heating system is no longer required. This is the argument of Cost Efficient Passive Houses as European Standards (CEPHEUS), an EU-funded Passivhaus demonstration project. The standard used includes the following minimum specifications (the U-value is a measure of insulation value, with a lower value being better):

  • Envelope: Well insulated: U-value: 0.2W/m2K. Airtightness: < 0.6 air changes per hour @ 50 Pascals (meaning hardly any air leakage). Low thermal bridging.
  • Glazing: Orientation and area optimised; approximately 250 per cent of floor area. Double glazing with low-e coating and insulated shutters or blinds, average U-value: 1.3W/m2K
  • Ventilation: Mechanical ventilation with heat recovery 70 per cent efficient. Supplementary heating via booster coil within air supply.

This standard approaches the Passivhaus standard. Some buildings cannot be upgraded this much. Therefore I would argue for a programme upgrading those which can and replaing the rest with new-build to the same standard or Passivhaus as far as possible. The point is that Passivhaus is a measurable absolute standard, while a percentage reduction is relative, and often to an unknown starting point.

Known unknowns

There are plenty of other unknowns, where more research is needed. One example is in the hygroscopicity of materials (their ability to absorb and release moisture), which is important for addressing damp. I believe that a huge leap is required in our understanding of the way that damp and heat moves through buildings and materials, how energy is used, and how people live in their homes, so they can be better designed to save energy.

There is a strong argument that less is more in sustainable refurbishment. The planning stage is where a good investment of time should be made to minimise mistakes and maximise savings. This may help to avoid 'eco-cliches' such as thoughtlessly applied micro-wind turbines, photovoltaic panels on buildings with inefficient electrical appliances and heat pumps in badly insulated buildings, described by the architect Howard Liddell when he coined the phrase 'eco-minimalism'.

In my research I saw a house with no less than six different and expensive sources of renewable energy, but with a complete absence of draughtproofing. I saw a cutting edge passive house which had an oversized wood pellet boiler that meant the householder regularly used mains electricity for showers, because running the boiler overheated the house.

We must beware of apparent solutions offered by particular manufacturers, which may solve one problem but do not address all aspects of low impact housing. Too many demonstration homes are sponsored by companies for this purpose.

Material matters

The choice of materials is important too, in terms of overall carbon reduction. It is vitally relevant that concrete and petrochemical-derived insulants emit carbon dioxide in their manufacture, whereas natural fibre ones such as cellulose lock up atmospheric carbon in the fabric of a building and enable a structure to breathe. We should therefore favour materials that lock up carbon, and frown on those which have a high embodied energy.

Renovating the whole of the UK's housing stock is a huge challenge. We can achieve a lot with currently available technology, but only if we act with absolute urgency.

Sustainable refurbishment Sustainable Home Refurbishment: The Earthscan Expert Guide to Retrofitting Homes for Efficiency, by David Thorpe, is out now, published by Earthscan. Ecologist readers can buy the book with a 20 per cent discount by visiting the Earthscan website, and entering the offer code REFURB10 at the checkout
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