1、Page52-Page62Low energy techniques for housingIt would appear that,for the industrialised countries,the best chance of rescue lies with the built environment because buildings in use or in the course of erection are the biggest single indirect source of carbon emissions generated by burning fossil f
2、uels,accounting for over 50 per cent of total emissions.If you add the transport costs generated by buildings the UK government estimate is 75 per cent.It is the built environment which is the sector that can most easily accommodate fairly rapid change without pain.In fact,upgrading buildings, espec
3、ially the lower end of the housing stock,creates a cluster of interlocking virtuous circles.Construction systems Having considered the challenge presented by global warming and the opportunities to generate fossil-free energy,it is now time to consider how the demand side of the energy equation can
4、respond to that challenge.The built environment is the greatest sectoral consumer of energy and,within that sector,housing is in pole position accounting for 28 per cent of all UK carbon dioxide （CO2） emissions.In the UK housing has traditionally been of masonry and since the early 1920s this has la
5、rgely been of cavity construction.The purpose was to ensure that a saturated external leaf would have no physical contact with the inner leaf apart from wall ties and that water would be discharged through weep holes at the damp-proof course level.Since the introduction of thermal regulations,initia
6、lly deemed necessary to conserve energy rather than the planet,it has been common practice to introduce insulation into the cavity.For a long time it was mandatory to preserve a space within the cavity and a long rearguard battle was fought by the traditionalists to preserve thissacred space.Defeat
7、was finally conceded when some extensive research by the Building Research Establishment found that there was no greater risk of damp penetration with filled cavities and in fact damp through condensation was reduced.Solid masonry walls with external insulation are common practice in continental Eur
8、ope and are beginning to make an appearance in the UK.In Cornwall the Penwith Housing Association has built apartments of this construction on the sea front, perhaps the most challenging of situations. The advantages of masonry construction are: It is a tried and tested technology familiar to house
9、building companies of all sizes. It is durable and generally risk free as regards catastrophic failurethough not entirely.A few years ago the entire outer leaf of a university building in Plymouth collapsed due to the fact that the wall ties had corroded. Exposed brickwork is a low maintenance syste
10、m; maintenance demands rise considerably if it receives a rendered finish. From the energy efficiency point of view,masonry homes have a relatively high thermal mass which is considerably improved if there are high density masonry internal walls and concrete floors.Framed constructionVolume house bu
11、ilders are increasingly resorting to timber-framed construction with a brick outer skin,making them appear identical to full masonry construction.The attraction is the speed of erection especially when elements are fabricated off site. However,there is an unfortunate history behind this system due t
12、o shortcomings in quality control.This can apply to timber which has not been adequately cured or seasoned.Framed buildings need to have a vapour barrier to walls as well as roofs. With timber framing it is difficult to avoid piercing the barrier.There can also be problems achieving internal fixings
13、.For the purist,the ultimate criticism is that it is illogical to have a framed building clad in masonry when it cries out for a panel,boarded,slate or tile hung external finish.Pressed steel frames for homes are now being vigorously promoted by the steel industry.The selling point is again speed of
14、 erection but with the added benefit of a guaranteed quality in terms of strength and durability of the material.From the energy point of view,framed buildings can accommodate high levels of insulation but have relatively poor thermal mass unless this is provided by floors and internal walls.Innovat
15、ive techniquesPermanent Insulation Formwork Systems （PIFS） are beginning to make an appearance in Britain.The principle behind PIFS is the use of precision moulded interlocking hollow blocks made from an insulation material,usually expanded polystyrene.They can be rapidly assembled on site and then
16、filled with pump grade concrete.When the concrete has set the result is a highly insulated wall ready for the installation of services and internal and exterior finishes.They can achieve a U-value as low as 0.11 W/m2K.Above three storeys the addition of steel reinforcement is necessary. The advantages of this system are: Design flexibility; almost any plan shape is possible. Ease and speed o
