ABSTRACT
The possibilities for building in wood have gradually increased in recent decades mainly due to environmental benefits. But there are still restrictions in terms of fire regulations in many countries, especially for taller buildings. The situation has therefore been mapped in about 40 countries on four continents as an update to a survey in 2002. The main issues are how high buildings with load-bearing wooden frames may be built and how much visible wood may be used both inside and outside on facades. The restrictions apply primarily to prescriptive fire design according to simplified design with detailed rules, which are mainly used for residential buildings and offices. For more complicated constructions e.g. public buildings, shopping centers, arenas and assembly halls, performance based design can be used by fire safety engineering design using, e.g. methods for evacuation and smoke filling, which increases the possibilities of using wood in buildings. The possibilities to use wood in buildings increase if sprinklers are installed, which is highlighted. Major differences between countries have been identified, both in terms of the number of storeys permitted in wood structures, and of the amounts of visible wood surfaces in interior and exterior applications. Several countries have no specific regulations, or do not limit the number of storeys in wooden buildings. The conclusion is that the differences are still large and that many countries have not yet started to use larger wood constructions despite supplies of forest resources, but harmonizing activities on performance based principles are ongoing worldwide.
Background
The combustibility of wood is one of the main reasons why many building regulations strongly restrict the use of wood as a building material. Fire safety is an important contribution to feeling safe, and an important criterion for the choice of materials for buildings. The main precondition for increased use of wood products and structures in buildings is adequate fire safety (Östman Citation2017). The regularitory situation was first presented twenty years ago (Östman and Rydholm Citation2002).
World-wide, several research projects on the fire behavior of wood structures have been conducted over recent decades, aimed at providing basic data and information on the fire safe use of wood in buildings. Novel fire design concepts and models have been developed, based on extensive testing and calculations. An overview has been published (Östman et al. Citation2017). The current improved knowledge in the area of fire design of wood structures, combined with technical measures, particularly sprinkler and smoke detection systems, and well-equipped fire services, allow the safe use of wood in a wide field of application. As a result, many countries are revising their fire regulations, thus permitting greater use of wood. Overviews are available (Östman et al. Citation2010, Mikkola and Pilar Citation2015).
Fire test and classification methods have been harmonized internationally, but regulatory requirements applicable to building types and end uses remain on national bases. Although these standards exist on the technical level, fire safety is governed by national legislation, and is thus on the political level, but further harmonization will hopefully provide means of achieving common national regulations.
This paper summarizes the present situation. Full information is given in (Östman Citation2021).
Fire safety in buildings
There are two different stages of a fire scenario to be considered in the fire safety design of buildings in relation to building materials and structures. These are the initial and the fully developed fire, see . In the initial fire, the building content e.g. furniture is of major importance both for the initiation of the fire and its development, but the building content is not regulated in building codes. Surface linings may contribute in the initial fire, especially in escape routes, since those are required to be without any furniture and furnishing. Limitations of the reaction to fire of surface linings are required in most national building codes. In the fully developed fire, i.e. after flashover in a room, the performance of load bearing and separating structures is important in order to limit the fire to the room or compartment of fire origin. This is called the fire resistance of the building structure.
Figure 1. The two main stages relevant for the fire safety in buildings in relation to building materials and structures.
Generally speaking, wood structures can obtain high performance for fire resistance and high levels for the separating and load-bearing capacity of wall and floor structures can be achieved, while the surface properties of wooden linings in the initial fire may be less favorable and also more difficult to quantify. The highest levels of the reaction to fire properties cannot be obtained by ordinary wood-based products.
National fire regulations
Questionnaire
In order to review the present situation, a questionnaire was sent to colleagues and contacts from international networks, e.g. FSUW Fire Safe Use of Wood. The response was very good and national information from 40 countries on four continents was received.
The questionnaire contained questions on requirements for residential and office buildings, some questions on possibilities for using performance-based design and space for commenting on specific items. The questions were given for design with and without sprinkler installations, which makes differences in some countries.
A main parameter was height of the building. It could be expressed in maximum number of storeys or in maximum height of the building in meters. These parameters are defined partly different in different countries and in some countries only one of the measures is used. The conversion between the two may also be different, so some simplifications have been used to present comparable data.
The building height has been grouped into 4 categories:
1–2 storeys
3–4 storeys
5–8 storeys
8 storeys incl. No Limits in some countries
Review results worldwide
The national information has been compiled in tables and maps. It is given separately for load-bearing wood elements, visible wood surfaces in interior applications and exterior applications as facades. These data are given both for residential and office buildings with and without sprinkler installations (Östman Citation2021).
As an example, maximum number of storeys allowed with load-bearing timber elements in residential buildings are summarized in and illustrated as maps in . Data for both unsprinkled and sprinkled buidlings are included.
Figure 2. Maximum number of storeys with load-bearing elements in wood in residential buildings acc. to prescriptive requirements; above without sprinklers and below with sprinklers installed. Preliminary data, final data in Östman (Citation2021).
Table 1. Maximum number of storeys/maximum height and fire resistance requirements on load-bearing elements in residential buildings – prescriptive / pre-accepted requirements. Preliminary data, final data in Östman (Citation2021).
Similar data for visible wood surfaces and official buildings are given in Östman (Citation2021).
Differences between European countries
The differences between European countries cannot be easily seen in , but are further detailed and in Östman (Citation2021).
Figure 3. Possibilities to use wood in different applications in Europe. Preliminary data, final data in Östman (Citation2021).
Conclusions
Major differences between countries have been identified, both in terms of the number of storeys permitted in wood structures, and of the amounts of visible wood surfaces in interior and exterior applications. The permitted use for structures and visible wood surfaces may be different within a country. The use of sprinklers facilitates the use of wood in several countries.
Several countries have no specific regulations, or do not limit the number of storeys in wooden buildings. However, a maximum of eight storeys is often used as a practical limit for wood structures. This limit may be higher for facades, linings and floorings, since these applications may also be used in, for example, concrete structures.
This information in this paper has to be treated with great caution, as there are often very detailed requirements and conditions that are difficult to simplify as a fair comparison between countries. There are also low requirements in certain countries that might be interpretated to indicate that the requirements in other countries are too strict, where in fact the opposite may be true i.e. the requirements in some countries may be inadequate (or silent in respect of tall timber buildings).
The information is therefore mainly an indication of regulatory differences in prescriptive requirements. For real building projects, the full regulations must be consulted and performance based alternatives may be available especially for larger and more complex buildings.
Acknowledgements
Many colleagues from international networks, e.g. FSUW Fire Safe Use of Wood have contributed with national information. Without their input it would not have been possible to compile this survey. Further details in the full report (Östman Citation2021).
Disclosure statement
No potential conflict of interest was reported by the author(s).
References
- Mikkola, E. and Pilar, M. G. (2015) Bio-based products and national fire safety requirements. COST Action FP1404, Workshop Berlin.
- Östman, B. (2017) Fire performance of wood products and timber structures. International Wood Products Journal, 8(2), 74–79.
- Östman, B. (2021) National fire regulations for the use of wood in buildings – worldwide review 2020. Report Linnaeus University.
- Östman, B. and Rydholm, D. (2002) National fire regulations in relation to the use of wood in European and some other countries 2002. Trätek Publication 0212044.
- Östman, B., Brandon, D. and Frantzich, H. (2017) Fire safety engineering in timber buildings. Fire Safety Journal, 91, 11–20.
- Östman, B., Mikkola, E., Stein, R., Frangi, A., König, J., Dhima, D., Hakkarainen, T., Bregulla, J. (2010) Fire safety in timber buildings – technical guideline for Europe. SP Report 2010:19. Stockholm, Sweden.