Off-site methods are evolving, and many of the traditional ‘pros and cons’ lists between ‘on site’ and ‘off site’ need revising.
Take the matter of speed of construction. It’s long been held that timber frame (i.e. off site) is ‘quicker’ than blockwork (i.e. built on site). There are two reasons for this. One concerns the fact that because the frame is built off site in a factory, the sitework is simply a matter of erecting the frame, which takes just a few days. The other reason is that the frame is independent of the external wall cladding, so that, once it’s erected, work can then follow on inside and outside simultaneously.
But the block makers came up with the thin-joint system, which not only speeds up the blocklaying process but also allows for the external claddings to be carried out independently, thus cancelling out much of the advantage for timber frame.
But timber frame doesn’t stand still either. Further speed advantages have been developed in Scotland, where the vast majority of detached homes are built using timber frame methods. The Scots have developed a different building process which simplifies the processes involved, and this saves between £1,000-£2,000 per house. Rather than erecting the entire frame at once, the internal walls are kept back in the build process until the external walls and ceilings have been boarded: this saves a huge amount of time spent nailing in supporting noggings. To get this advantage, the Scottish erection crews (known as the roughing joiners) have had to learn other skills, notably insulating and plasterboarding, so the old demarcations between joiners and plasterers has gone by the wayside.
Many timber framers are also beginning to use SIPs (structural insulated panels). The processes involved are similar – both are very much off-site systems – but SIPs come pre-insulated, thus making for further speed savings. SIPs tend to be a little more expensive than timber frame but as the demands for ever-lower U-values continues apace, the cost differential narrows. SIPs are particularly quick when used to make open roof areas, as the roof can be laid in panels across supporting beams. Although there is nothing, in theory, to stop you putting a SIP roof on top of a masonry structure below, in practice it’s something many SIPs suppliers have grown wary of, having encountered problems over the years making up roof panels for plans which are then not built accurately on site.
ABOVE: SIPs are a pre-insulated form of timber frame, manufactured off site, making for an energy-efficient, fast construction method; Screedflo dB is pumped onto timber floors, providing an acoustic barrier and a medium for underfloor heating; A timber frame during construction; Weatherboarding is the perfect cladding for timber frame properties.
Many people steer away from timber frame because they assume that it will be noisy and that sound will carry through walls and, particularly, through floors. In fact, a lot of self-builders choose masonry construction for no other reason than it allows them to build with a precast concrete intermediate floor in order to keep the house quiet.
But now you can get timber frame floors with a poured screed, which offers sound reduction every bit as good, if not better than, precast concrete. Screedflo dB, as its name suggests, is designed to be pumped onto timber floors both as an acoustic barrier and as a medium for underfloor heating. The system has to be designed from the outset – it can’t be installed as an afterthought – and it involves laying 10mm of acoustic foam and 25mm of high-density fibreboard under a layer of polythene sheeting. The anhydrite screed is then poured in a brief visit and left to set overnight. You can lay underfloor heating pipes within the screed, thus greatly simplifying the process (screedflo.co.uk).
Whilst you can place any cladding against any background, some go better together than others. Lightweight claddings – and this includes tiles and rainscreens as well as weatherboarding – work incredibly well with framed constructions because you can fix them onto battening which is itself fixed onto the subframe. Not only is this quick and easy to do, but it greatly reduces the width of external wall. Instead of a typical 325mm profile where brick or stone are used, you can build external walls at a thickness of just 225mm. That’s enough to increase your floor area by 4% overall.
ABOVE, CLOCKWISE FROM TOP: In Scotland, 75% of new houses are timber frame; Timber frame makes for some of the most striking designs; Timber frame can be used on even unusually shaped houses, like this eco-friendly curved property; Timber frame can be clad in any material – this flint and brick-clad house belies its timber roots.
Timber Frame – A Rising Sensation
In recent history almost all houses in the UK have been built from masonry blockwork — with timber frame, certainly in some areas, being seen as niche. This is with the exception of Scotland, which has always largely built with timber frame. However, in recent years, concrete’s dominance has come under threat significantly from the rising popularity of timber frame construction. Recently published statistics from the UK Timber Frame Association (UKTFA) are testament to this, reporting that the market share for timber frame has risen for the tenth year in a row, up from 8% in 1998 to 25% in 2008. In Scotland, timber frame’s market share is over 75% and still rising.
Geoff Arnold, Chairman of the UKTFA, explains: “The timber frame industry in the UK has continued to show its strength, resilience and maturity despite these difficult times for homebuilding and the housing market. Timber frame is the right building solution for now and the future as it has the ability to comply with and exceed current forthcoming Building Regulations. Timber frame also performs better than any other building material in meeting the need to build sustainable homes and the speed and efficiency of construction delivers the best economic solution for customers.
“When the economic upturn comes and the urgent need for fast, sustainable building becomes even more critical, timber frame looks set to be the number one choice. The timber frame industry can look to the future with real confidence.”