Triple glazing in timber frames should be standard throughout, achieving a U-value of less than 1.0W/m2K. However, even these may be vulnerable to failure in super-storms.This is one of several reasons for recommending a return to the traditional practice of fitting external shutters, which also protect against extreme temperatures.‘Concertina’ type shutters regularly feature in new buildings in mainland Europe (Figure 5.1).
Sustainability approved hardwood external doors should exceed current thermal building
regulations and feature a window in toughened glass only large enough for identification purposes.
Where possible, houses should be orientated with their gable ends east–west with minimum openings. This will offer protection from prevailing winds. Where possible, natural wind breaks should be exploited.There is even a place for the Leylandii hedge, provided it is kept in check.
Temperature
In the formulation of building regulations like the UK’s Part L, the emphasis up to now has been on conserving warmth. In the future it is probable that keeping cool will be as important as retaining heat. In the government’s Planning Policy Statement: Eco-Towns, concerning standards for proposed eco-towns, it states that houses should ‘incorporate best practice on overheating’.This throws into doubt the viability of lightweight structures that can be efficient at retaining heat but are deficient in avoiding overheating.
A Met Office report commissioned by the Department of Works and Pensions in 2008 concluded that ‘the weather may become so hot that Britain’s poor and elderly will need state help to pay their summer energy bills as they reach for air conditioners to prevent themselves dying from heat exhaustion’. The report concluded that, by 2050, summers of the intensity of 2003 will occur every other year (Guardian, 8 January 2009, p9). It is worth repeating the TCPA warning in Chapter 2 to expect 40–48°C summers.
The UK has adopted the target of 2 million new homes by 2016 and 3 million by 2020.This was repeated at a time when the construction of new homes had almost come to a halt as contractors were denied loan facilities. The official view is that the only way such targets can be realized is if offsite, factory prefabrication is optimized.This favours timber frame lightweight construction as demonstrated by the Innovation exhibition at the BRE, featured in Chapter 4. The advantages are speed of erection and cost.
44 Building for a Changing Climate
The overriding disadvantages are that such construction techniques will be vulnerable to failure in hurricane scale storms, as mentioned, and that, as demonstration examples have shown, it can be difficult to achieve the Code level of air tightness.
Above all, the poor thermal mass of these buildings will create interiors that amplify the peaks of outside temperature but do not respond to the troughs. In others words high temperatures are sustained overnight. The killer factor in the 2003 heatwave was the persistence for weeks of night temperatures at around 35°C. This means that the zero carbon credentials of such houses will be compromised by the use of room-size air-cooling units in high summer, especially at night.
As discussed in Chapter 4, the Hanson 2 house at the BRE exhibition was the only one that achieved anything approaching a significant capacity of thermal mass. This capacity is where the specification for storm protection coincides with the need for thermal mass and is an issue that should be considered separately from thermal efficiency as defined by U-values. This reinforces the argument in favour of at least 240mm of masonry in external walls. At least 150mm of insulation should be incorporated to meet Code 6 thermal requirements (see Figure 5.5 below).
A further advantage of masonry construction is that it is more efficient at achieving the mandatory level of air tightness than lightweight structures, which, as mentioned have encountered difficulties in this respect.
Thermal mass, or volumetric heat capacity (VHC), is the ability of a material to store heat or cooling when subject to a temperature change, without undergoing a phase change. It is measured in kilojoules/m2 K. Typical values are: concrete 2060 and brickwork 1360. So, high thermal mass evens out the peaks and troughs of the external temperature. In winter it stores heat and in summer reduces heat absorption whilst also facilitating night time purging. In houses this can be achieved passively. The BedZed and RuralZed projects
employ rooftop cowls that have vanes that orientate the cowl to the prevailing wind. This means that the ventilation inlet faces upwind and exhaust air is extracted by suction downwind. In winter a heat exchanger transfers the warmth from the exhaust air to the incoming fresh air (see Figure 4.11).
It has been estimated that the ‘thermal lag’ in a high thermal mass office building can be six hours. As climate impacts gather momentum, it will be likely that building regulations will have to include minimum standards for thermal mass (RIBA, 2007).
Phase change materials (PCMs) can supplement thermal mass. PCM plaster contains nodules of wax that change from a liquid to a solid and vice versa according to the temperature, thereby absorbing or releasing heat. PCMs can be located in ceiling voids into which air is drawn by a fan, either to be recirculated in during the day or released to the exterior for night time cooling.2
There may be objections to these recommendations on the grounds that heavyweight construction involves substantially more embodied energy than the lightweight counterpart.The repost is that it will have a long life expectancy as a whole and in respect of its components. This comes at a price. However, according to engineering consultants Atelier Ten, ‘High mass, conventional buildings with tested conventional materials have a much longer life in use than lightweight construction. The lifespan of many lightweight buildings, with their reliance on mastics and exposed metals, is often quite short – as little as 25 years is not uncommon. On the other hand, conventional and traditional buildings have been shown to last hundreds of years.’
In many instances the on-costs could be offset by lower insurance premiums. Where homes are due to be built on flood plains only radical measures may make properties insurable. There is always the ‘peace of mind’ factor of a property that will appreciate in value as the effects of climate change become ever more apparent.