PPG3's demands for higher density and improved design quality, allied with ever more stringent Building Regulations, are driving change in the traditional housebuilding process and the materials used, and are eliminating the words "standard housetype" from the housebuilding lexicon.
"PPG3 has created two diverse tranches of design," says David Birkbeck, chief executive of housing design lobby group Design for Homes. "There is historic styling where housebuilders are likely to use better quality brick, and finishes like render and weatherboarding, which is replacing the standard housetype. And in urban locations there are more modern designs, using more precise, mathematical materials like glass and wire-cut bricks." The changing face of the PPG3-compliant house is charted in a Design for Homes survey, which was carried out by Maven Management. The survey notes housebuilder interest in a variety of finishes, and a large increase in the popularity of render.
The simple fact that PPG3 requires homes to be linked, as apartments and terraced houses, is having an impact on construction. "People are having a serious look at acoustics," says Kendrick Jackson, managing director of housebuilding industry consultant KJ Technical Services. Acoustic standards are to be improved under the revision of Part E of the Building Regulations, which is planning to give housebuilders the option of either having acoustic testing carried out on their homes, or building using the approved construction methods known as robust standard details. "I think the RSDs will be adopted quite strongly," says Jackson. "Housebuilders will prefer the security of them."
The increase in linked housing has inherently increased the thermal efficiency of new homes, but energy efficiency standards are steadily being made more rigorous under revision of Part L of the Building Regulations. The full impact of last year's revision of Part L is now becoming apparent, and evidence suggests that in seeking to meet new wall U-values of 0.35 W/m2K, many housebuilders are opting for partial-fill cavity walls. "A step change has taken place and partial fill cavity walls are becoming more the norm," says Jackson.
To achieve greater thermal efficiency in walls, housebuilders can either increase the thickness of the wall itself, or build it from more energy-efficient materials. Manufacturers of such materials say that many housebuilders are opting for the latter course, with Kingspan reporting a big increase in sales of its polyurethane insulation and H+H Celcon seeing a similar growth in sales of its aircrete blocks. "Housebuilders don't want to go to increased wall thicknesses and redesign their housetypes," says John Garbutt, marketing manager of Kingspan.
With the potential for wall U-values to drop as low as 0.25 W/m2K or even 0.15 W/m2K in the next revision of Part L, which is already coming under debate, housebuilders and manufacturers could be facing a far more radical shift in build technology. "It will be a quite significant change," says Jackson. "The last revision to Part L allowed people to increase efficiency and keep within a 300 mm wall zone. It will be more difficult next time. People may have to rethink how they build and move to framed solutions."
Manufacturers say that they are ready for the next change. "Aircrete will be able to provide good solutions," says Ian Exall, marketing manager of H+H Celcon.
"U-values may not be the only issue in Part L in the future. Other factors such as airtightness and thermal E E mass could come into consideration. It may not only be the insulating factor of the material that is important."
"Our new machine can make insulation board up to 200 mm thick, so we are capable of making what the changes in the next regulations will demand," says Kingspan's Garbutt. "But to go from a U-value of 0.35 to 0.25 is a massive change."
Forward-thinking housebuilders are also planning ahead. Redrow Homes has spent six months creating new house layouts, to be introduced next year, that have been designed to be built either traditionally or in steel frame. "We're trying to make sure we combine the best way of designing the product with the most efficient way of building it. We've simplified the build process, but not sacrificed the kerb appeal," says Paul Pedley, chief executive with the company.
Redrow has entered into a joint venture with Corus, called Framing Solutions, that will see all Redrow's regional divisions testing steel-frame construction on one of their sites over the coming months. "The build programme is very different. We realised we need more site resources far quicker. That is why we have chosen to trial this on one site per region, so that we can all go through the learning curve. Then when we know it works, we'll roll it out," says Pedley. "We have to accept that we as an industry are moving more towards manufacturing. Two years ago, the cost equation favoured traditional construction. Now steel frame is cost neutral, and labour-only subcontractors are getting more expensive by the day. One of the biggest advantages is taking weather out of the system. We build in 18 weeks by traditional construction but 12 weeks using steel."
But Design for Homes' survey found that housebuilders are not enthusiastic about all modern methods of construction. Although almost 50% of housebuilders are investigating timber frame, not one company surveyed said it was looking at modular/volumetric building, although it has been trialled by Sunley Estates and George Wimpey in the private sector and London housing association the Peabody Trust, and others, in the affordable sector. "The problem with volumetric is that it means that housebuilders have to write out one cheque to a single manufacturer – and they have to do it upfront," says Design for Homes' Birkbeck. "But it doesn't mean housebuilders are not interested in innovation."
In fact, when the survey asked housebuilders what they wanted from their suppliers, they enthusiastically responded that they wanted more alternative methods of wall and floor construction, and more panel cladding systems. "There is more scope for lightweight cladding, but when you go to manufacturers the product is not available," says Redrow's Pedley. "We're having to work with suppliers, and we are finding more willingness among suppliers to do that. For example, for chimneys we now use steel structures with brick slips on. But at the same time, we don't want to lose the distinctive look of our streetscenes."