Multi-storey buildings
In many countries national building regulations have tended to restrict the use of timber frames for the construction of multi-storey buildings. The reason many countries have refrained from using flammable materials is uncertainty about fires in the buildings. However, extensive research and development has shown that material-neutral building regulations are preferable and for over a decade function-based regulations have been common in many countries. Wood as such burns, but it does so in a controlled manner. It is possible to estimate how much of the cross section will remain unaffected by the fire after one hour of burning and choose material dimensions so that the unaffected part of the cross section has the ability to bear the required load. Steel, on the other hand, loses its entire load-bearing capacity at the temperatures that are produced during a fully developed fire. Non-flammable surface materials and/or sprinklers can be used to ensure safety during the early stages of a fire.
Modern building regulations have contributed to the increase, now taking place, in the construction of tall multi-storey timber buildings of between three and eight storeys. The dramatic increase can be attributed to several important factors. One of these is the lower cost of building compared with construction using other materials. Timber has shown to be the perfect material for use with industrial building methods, enabling costs to be reduced.
Another factor is the growing environmental awareness where the choice is motivated by the fact that timber is a renewable material and that its use reduces CO2 emissions, provided that the timber is harvested in forests where sustainable forestry is practised, with replanting and management plans.
Another factor worth mentioning is the possibility of building on sites that with heavier buildings, e.g. those made of concrete, would demand extensive and expensive pile foundations. Formerly uncertain or impossible sites can thus be used for lighter timber constructions and therefore with simpler and inexpensive foundations.
The design in terms of horizontal stability is especially important because the construction is relatively light. A common practice for buildings with 6-7 floors is to build the ground floor in concrete and secure the timber structure to the concrete. The load from the wind is transformed via joist elements and shear walls to the ground. Good stability is achieved by utilising diaphragm action. An important consideration when designing multi-storey buildings with a load-bearing wood frame is stability in relation to noise. Effective solutions are now available to prevent sound from spreading between the floors and apartments without putting the stability of the building at risk.
In the same way as with single-family houses, multi-storey buildings made of timber can be given an outer architectural design that suits the location where the building is erected.
Single-Family Houses
Wood frame is the most frequently used system for single-family houses. It is also common for single-family houses to be built using prefabricated components. This construction method allows for major variations in the design of the houses conforming to national and local building traditions while permitting architectural innovation. To a large extent the design determines the cost of the building and there are also variations here, from deluxe homes to extremely cost-effective single-family houses at prices that are acceptable to the average family. The requirements for fire safety and noise pollution are usually lower for single-family houses than for multi-storey buildings. It is, however, harder to satisfy the demands for low-energy consumption in a single-family house.