Timber has long been used as a structural material, dating back many centuries. As time goes on, advancements in the various types of wood components available and their use in various structural forms have occurred; new advanced timber products are now available, allowing structural engineers to achieve the performance and efficiency in building forms that are required in the twenty-first century.
There are thousands of tree species from which to source timber, each with its own growth rates, structural qualities, and levels of durability. The timber supply chain has adjusted to the unpredictable nature of nature and now provides consistent product supply from managed forests. The industry has also developed grading processes to ensure that these items have consistent technical performance (grades).
Timber is categorised as either ‘softwood’ or ‘hardwood’. Softwood is obtained from coniferous trees and hardwood comes from broad-leaved trees. Softwood and hardwood are botanical terms and do not necessarily refer to the density or hardness of the wood. For example Balsa, which is known to be soft and used for building lightweight models, is a hardwood whereas Douglas Fir is a softwood with good durability and high strength properties.
Softwood is commonly used for timber structures as it is readily available, easily worked, of relatively low cost and its fast rate of growth gives a continuous supply from regenerated forest areas.
Hardwoods are typically used for exposed structures and claddings where durability and particular aesthetic characteristics, such as colour or grain pattern, are required.
History of Use
In the United Kingdom, timber was the principle construction material for buildings in the Medieval period until the 18th century. After the Great Fire of London in 1666, masonry was used increasingly for external and separating walls with structural timber employed for roofs, floors and internal walls.
Oak was typically used for timber-framed buildings during the medieval period due to its availability, while softwoods from the Baltic countries and North America were increasingly employed for internal structural timber, floors and roofs within masonry buildings from the 18th century onwards.
With the increasing use of iron in buildings in the 19th century, timber was used in combination with metal for long span and heavily loaded structures. The development of mathematical procedures at this time for the design of structures and structural elements led to today’s approach to engineering timber structures.
How is timber strength graded?
Timber intended for structural use must be strength graded, to give a basic prediction of its structural performance and ensure it is at least strong enough for the highest expected load.
Timber is graded in accordance with BS EN 14081.
Strength grading can be carried out by visual inspection according to strictly defined rules, or by a grading machine.
Once the strength grade is known, together with the species, a strength class can be assigned, which leads to the characteristic values needed for structural design. Strength-graded timber must be CE marked under the Construction Products Regulation (CPR).
Why use timber for today’s structures?
When it comes to developing your new home, renovating your current home or even considering building an addition to your home there are many options to choose from when it comes to framing. But have you ever considered timber as your chosen material? Or questioned why you should?
- Sustainability – custom timber frames are recyclable and sustainable. Sustainable wood provides a natural and eco friendly solution to many of the material resource problems we face today. Sustainable timber produced from well-managed sources is considered to be one of the planet’s most valuable resource.
- Insulation – timber frames allow more space for natural insulation than a brick building, making it less expensive to maintain a comfortable, energy-efficient interior environment.
- Quality and Durability – timber can withstand a great deal of unpredictable weather conditions and impacts. When properly maintained, timber can last up to 40 years.