Paul Newman of Potton Self Build explains the ins and outs of offsite construction, and the many benefits it holds for self builders
In many people’s minds, construction still happens ‘brick by brick’ on a building site. With the advent of offsite construction, however, more and more of the building process is happening in a factory environment. Contrary to what the term might suggest, offsite construction isn’t necessarily the delivery of a fully built house on the back of a lorry. It just means that elements of the build – in the case of timber-frame construction, the wall panels, roof structure, and potentially floor structure – are manufactured and part assembled in a factory. These sections are then delivered to site and the superstructure is erected. There are a number of important benefits to this prefabricated approach to housebuilding.
Offsite construction is often offered as a package by companies, most of whom will deliver a build to a weathertight stage, and some of whom will offer a design service too. This ensures that the company has sole contractual responsibility for all of those build elements, so you know exactly who to contact if necessary.
As you’d expect, the part-assembled nature of buildings constructed using timber frame means that, once the kit is delivered to site, this construction occurs extremely rapidly. Often, the superstructure is standing within a matter of weeks. This delivers it to a weathertight stage much sooner than a masonry build, allowing internal works to quickly start alongside external ones like cladding. Because of this, bricklaying can be removed from ‘critical paths’ in the construction programme.
The erection of a timber frame conforms to what’s known as a ‘dry’ method of building. This comes in very handy in the unpredictable (and often soggy) climes of the UK. Essentially, unless strong winds mean the operation of a crane is unsafe, there is virtually nothing to stop timber frames being erected. Where masonry builds have to stop, sometimes for weeks, because of wet or cold weather, timber frames can continue unimpeded.
QUALITY AND HEALTH & SAFETY
As offsite construction takes place in a factory, it’s far easier to control the quality and manage any potential variables. Every panel is measured and manufactured exactly to the standards of the specific design, which produces a high level of dimensional accuracy. This higher level of accuracy allows for increased cost certainty, in comparison to other build methods. It also makes build times much more predictable, as there are virtually no ‘unknowns’ with a timber-frame build, which could otherwise incur significant delays and therefore additional cost.
The quality of the finished goods is checked and verified even before they leave the factory. Factory Production Control systems are used which cover manufacturing quality, health and safety and environmental sustainability, and these are audited independently each year. Moreover, by moving work that would otherwise be carried out onsite into a quality-controlled factory environment, health and safety performance is significantly improved.
Timber frame is one of the most sustainable mainstream construction methods. FSC and PEFC certification bodies ensure the timber and timber products are sourced from sustainable forests, which plant more trees than they harvest. Even the OSB (oriented strand board), chipboard, and plywood that make up offsite panels and/or floors is harvested from sustainably sourced timber.
Lower embodied energy also factors into the sustainability of timber-frame build systems. This is the amount of energy required to cultivate, harvest, and manufacture the timber frames, and it is significantly lower than other build methods, most of which require heat to extract and manufacture them. This means timber frames have a lower carbon footprint than other mainstream construction methods. Wood is also a ‘carbon store,’ i.e. using timber will retain carbon that would otherwise have contributed to greenhouse gases. Manufacturing the timber panels in factory conditions also ensures much less waste than a wholly onsite build.
Panels used in timber frame construction are filled with insulation, making it easier to achieve levels of performance that exceed those required by Building Regulations. When considering the performance of a building as a whole, the performance of external wall junctions in timber-frame buildings typically significantly exceeds that of masonry builds. As well as the walls being easier to insulate to higher levels, building with timber frame also facilitates all of the building’s external wall junctions being made more efficient overall.
The offsite nature of timber-frame construction carries many benefits. Build times with offsite construction are incredibly fast thanks to the factory- manufactured and part-assembled timber-frame panels. Cost certainty is easier to achieve, as is the predictability of the build time because of the dry nature of the construction method. Finally, the ability to achieve greater sustainability is another reason why offsite construction is increasingly used in housebuilding, and its use will only continue to grow.
Paul Newman is director of Potton Self Build