【正文】 uilt environment which is the sector that can most easily acmodate fairly rapid change without fact,upgrading buildings, especially 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 fossilfree energy,it is now time to consider how the demand side of the energy equation can respond to that 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 largely been of cavity 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 dampproof course the introduction of thermal regulations,initially deemed necessary to conserve energy rather than the pla,it has been mon practice to introduce insulation into the 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 this‘sacred space’.Defeat was finally conceded when some extensive research by the Building Research Establishment found that there was no greater risk of damp peration with filled cavities and in fact damp through condensation was reduced. Solid masonry walls with external insulation are mon practice in continental Europe and are beginning to make an appearance in the 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 building panies of all sizes. ● It is durable and generally risk free as regards catastrophic failure–though not 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 system。 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 construction Volume house builders are increasingly resorting to timberframed construction with a brick outer skin,making them appear identical to full masonry attraction is the speed of erection especially when elements are fabricated off site. However,there is an unfortunate history behind this system due to shortings in quality can apply to timber which has not been adequately cured or buildings need to have a vapour barrier to walls as well as roofs. With timber framing it is difficult to avoid piercing the can also be problems achieving internal 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 selling point is again speed of 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 acmodate high levels of insulation but have relatively poor thermal mass unless this is provided by floors and internal walls. Innovative techniques Permanent Insulation Formwork Systems (PIFS) are beginning to make an appearance in principle behind PIFS is the use of precision moulded interlocking hollow blocks made from an insulation material,usually expanded can be rapidly assembled on site and then filled with pump grade the concrete has set the result is a highly insulated wall ready for the installation of services and internal and exterior can achieve a Uvalue as low as W/ three storeys the addition of steel reinforcement is necessary. The advantages of this system are: ● Design flexibility。skill requirements are modest which is why it has proved popular with the selfbuild erectors can achieve 5 m2 per man hour for erection and placement of concrete. ● The finished product has high structural strength together with c