Living in the Goldilocks zone

To describe the narrow range of conditions necessary for planetary life, Dr James Lovelock, proponent of the Gaia hypothesis, coined the phrase the “Goldilocks phenomenon”, referring, of course, to how she preferred her porridge “neither too hot, nor too cold”.

Although Lovelock was looking from a cosmological perspective, the principle holds true at a micro level. For example, Great Britain is nestled in its own “Goldilocks zone”. We are surrounded by the Gulf Stream and a large sea mass, which lift the temperature we would otherwise experience at our latitude. We are therefore caught midway between Scandinavia and the Mediterranean and enjoy a climate that is neither as severe as the former nor as sun-kissed as the latter. This is why, for example, the German PassivHaus design standards, formulated for central continental Europe, must be adapted for use in the UK (see 'PassivHaus: Adapting our homes to climate change' at end).

Although there is a scientific consensus that the global climate is changing, there is less agreement on where that change is ultimately taking us. With a possible long-term disruption to the Gulf Stream due to polar ice melting, our climate could become more like North America, Canada and Northern Europe with significantly cooler year-round temperatures and severe winters or, as seems more likely in the short to medium term, it could grow warmer with seasons merging into one long hot summer.

In simple terms, are we going to be hit by another cyclical ice age or will global warming get there first and turn us into a desert? As this is an unknown number of decades into the future, it is easy to put it aside and refocus on more immediate challenges. However, one such challenge set by the government is the start of our most ambitious housebuilding programme for more than 50 years. Targeted to create three million new homes, there is every possibility that the fruits of this endeavour will still be occupied after our climate has changed – and there’s the issue for the construction industry.

To live comfortably and sustainably in a changeable climate requires a different attitude to building methodology. If we are going the way of Canada, Scandinavia and points North, we should be building highly insulated timber frame homes. If we are heading towards a Costa del Bognor, we need the thermal mass of brick, concrete, stone and block. And with both options, what other technologies will be needed to maintain our comfort?

The two building methods absorb and dissipate the sun’s heat very differently. As the graphic at the end of the article shows, a building with high thermal mass behaves like a slow-motion storage heater, storing heat within the fabric for long periods during the day and releasing heat overnight, while a timber frame works like a thermos flask, absorbing heat more rapidly – and trapping it within the internal space.

A home with a highly exposed thermal mass will stay relatively cool in summer and if used continuously can be efficiently heated in winter, aided by external insulation and passive solar gains to store energy in the internal structure and release it slowly at night. A key feature here is big windows with shading that let in solar radiation in autumn and winter when the sun is low and block it in summer.

A well insulated timber frame home will also maintain a comfortable internal temperature in winter by trapping what little heat the sun gives at this time inside the building. However, that advantage can easily lead to overheating even during an average British summer.

With timber frame, and to some extent thermal mass, the major challenge during extended periods of high temperatures is therefore internal overheating. Of course, this can easily be overcome by installing comfort cooling, popular in the US and increasingly in Europe, but that rather flies in the face of energy conservation. Instead, both timber frame and thermal mass buildings need to be coupled with energy efficient ventilation and effective solar shading (see 'Options for energy-efficient ventilation and effective solar shading' at end).

A recent publication by the Chartered Institute of Building Services Engineers, Climate Change and the Indoor Environment: Impacts and Adaptation, studied the likely effects of climate change on three housing construction types (low, medium and high thermal mass) and several types of dwellings (including 19th century houses, 1960s flats and new build flats and houses) over a 100-year period of temperature rise due to climate change using the 2020s, 2050s and 2080s as the sample test dates.

The report shows that the internal temperatures of timber frame and thermal mass buildings increase as the external temperature rises over the test periods (in London the rise is between 3.6 – 6°K). However, all building types where solar shading, ventilation and internal heat gains are controllable should meet recognised internal comfort levels of 25-28°C for living areas and 21-25°C for sleeping areas until the 2050s – but only high thermal mass buildings with solar shading and controlled ventilation are projected to meet these levels into the 2080s and beyond.

Timber frame is becoming increasingly popular – it is quick, sustainable, energy efficient, produces little waste, facilitates off-site construction and is cost-effective. For commissioning bodies in the public sector and developers in the private sector these benefits, linked with solar shading and ventilation, outweigh the potential downside.

Once timber frame incorporates additional energy-efficient technologies to counter the possibility of overheating in summer, its full potential will be realised.

Meanwhile, work continues. In Denmark, for example, sustainability expert Ivan Lyngby is looking at how sustainable construction can meet the climate challenge and a small housing development has been constructed based on his findings. The building is constructed with aircrete blocks with external insulation and exposed internal thermal mass; all triple-glazed windows (U value 0.8) have automatic external blinds and incorporate passive solar heating and effective solar shading. Sustainable technologies include solar thermal water heating, whole house ventilation with heat recovery, photovoltaics and ground source heat pumps.

While these are all familiar in the UK, the clever bit is the control system that links these elements and maximises the efficiency of both passive and active technologies. This simple innovation confirms the effectiveness of the holistic approach – no one solution holds all the answers and building comfort into buildings for an uncertain future climate requires a willingness to harness passive and active energy technologies. After all, our future is unlikely to be as simple as either arid desert or artic tundra.