The case for timber

Timber materials have been used in the construction industry for centuries. In developed countries over 70% of people live in timber framed housing, which accounts for 90% of low-rise buildings in the US and Canada. In the UK one in six homes is timber frame built and wood is also being adopted in sectors such as schools, offices and hotels amongst many others.

Although there has been a certain amount of timber substitution by other materials, such as traditional brick and block, plastic windows and roofline products, timber continues to be an important building material.

With spiralling energy costs and unpredicted international demand forcing material suppliers to raise the cost of core supplies, developers are beginning to question the structural design options available to minimise these cost impacts. The cost of producing timber products has not been subjected to the same level of input price rises as other structural components, such as brick and block, concrete or steel, due to its lower consumption of energy and sustainable supply.

There are many forms of timber frame, including open panel, advanced and closed panel, volumetric and hybrid systems. Timber frame, traditionally associated with low-rise construction, can now be built up to eight storeys high and, like all methods of construction, conforms to the requirements of the building regulations.

In the UK, timber frame construction is based on factory-made structural elements such as wall panels which carry the loads on the building to the foundations. The outer cladding, which can be made from a wide range of materials including brick, stone or lightweight claddings (such as timber boarding, tile hanging or render) provides decoration and weather protection. Factory-made panels are accurately manufactured to precise tolerances in a controlled environment away from the unpredictable weather.

Environmental impact

The savings of construction time, reduced site work and the potential price reductions of manufactured components can lead to WLC savings for timber

Timber is an organic, non-toxic and naturally renewable building material and in the UK is sourced from well managed softwood forests. Timber products have lower embedded energy and are recyclable, having less impact on the environment than masonry products. Timber is effectively a carbon-neutral material and has the lowest CO2 cost of any commercially available building material. About 77% of the energy used in the production of wood products comes from wood residues and recovered wood. In contrast concrete takes five times more energy to produce than timber.

A typical 100m2 two-storey detached timber frame home contains 5-6m3 more wood than the equivalent traditional brick and block house. In addition, the operational cost of a house can be reduced due to timber's thermal efficiency. Most wood products, from timber frame systems to joinery, can help designers and developers improve their EcoHomes ratings. Waste and end of life wood can also be easily recycled.

Construction efficiency

Timber frame has a 30% shorter, more predictable construction time than traditional brick and block. This makes for an improved investment return, reduced disruption to local communities and more efficient sites. A typical timber frame house can be weather-tight in less than five days and the construction can help to promote greater partnering, better control and project savings through improved supply chain integration. Dry construction not only saves time on site but means that decorations can be carried out soon after completion of the building without risk of cracking or deterioration of finishes.

Nevertheless, different project circumstances can favour or work against timber frame construction. Factory manufactured elements of a timber frame also mean that a larger proportion of cost is committed earlier and hence it is difficult to suspend operations if circumstances later change.

Factory manufactured elements of a timber frame mean that a larger proportion of cost is committed earlier and hence it is difficult to suspend operations

Whole life costs

There are many factors that contribute to the cost of a timber frame. The type of timber, the complexity and number of joints and the size of the frame all contribute to the overall cost. Costs also relate to issues such as access to the site, the provision of power and the availability of an area to put the frames together prior to erecting into position using cranes or winches.

Analyses showed that timber frame can be at least as competitive as traditional techniques in appropriate circumstances, although in many cases timber frame, except open panel, currently tends to be slightly more expensive than brick and block. Nevertheless, the savings of construction time, reduced site work and the potential price reductions of manufactured components as the market matures can lead to WLC savings for timber frame, which include earlier rental income or investment return, reduced snagging costs and reduced on-site costs.

For example, the costs of volumetric timber frame are incurred mostly off-site and the approach will be more competitive only if the costs of off-site components decrease. Figure 1 illustrates the capital costs comparison and Figure 2 demonstrates the cost savings. The open-panel timber frame construction is exceptional and cost competitive, currently costing £798/m2, compared to £799/m2 for traditional brick and block, according to the NAO. It requires 20% fewer on-site labour days and 30% less time to build than traditional brick and block. Table 1 presents the average elemental costs for timber framed housing, while figure 3 shows the average elemental analysis. Timber frame, as a type of modern method of construction, is seen as a cost effective approach for the future of the construction industry, in particular, the housing sector, and its further cost reduction depends on where costs occur, which varies for different construction methods.