Timber is one of the most versatile building materials on the planet. But too often the material is misused or incorrectly installed, compromising its properties. Stephanie McDonald reports.
One of the most important aspects of using timber is selecting the right species for the right application. Stephen Mitchell, sustainability programme manager at the NSW Timber Development Association, says other key characteristics which affect choice are strength, appearance, durability, moisture content - which affects shrinkage rates - density, hardness and fire indices.
He says some common mistakes are made by confusing the properties of timber, such as confusing structural grades with natural durability classes; confusing natural durability and preservative hazard classes; and specifying seasoned (kiln-dried) hardwood timber in sizes above 45mm thicknesses, which are hard to source or have long lead times.
"It is common for designers to have a good idea of what they want something to look like yet specify the wrong timber or detail to fit their idea. This is particularly the case in exposed external applications where natural durability, preservative treatment and finishes are all important considerations," Mitchell says.
Tim Sherry, marketing manager at Carter Holt Harvey, agrees, and says it is common for the wrong product to be used versus the architect's vision. "Timber selection is often driven by availability and pricing," he says.
Robyn Barnes, marketing manager at Boral Timber, says mistakes can also be made due to a lack of knowledge about timber. For example, not understanding the natural features and variations of timber. Also, over specifying the material can be a problem.
"Building designers are often driven by their goal of a particular aesthetic outcome, which means other attributes of a species selection, such as hardness ratings and certification, can be overlooked," Barnes says.
"We also find that because of the shared responsibility in building projects, the lack of detail when specifying can lead to ambiguity and the substitution of the wrong product, which may not meet the desired outcome."
Mistakes can also be made when it comes to installing timber, such as not installing enough structural bracing, particularly during construction, according to Mitchell.
Also, timber flooring installation needs adequate gaps around the wall so the timber can naturally expand and contract, which can be easily forgotten, according to Mitchell. He says inadequate drying out or drainage of the sub-floor area and not taking into account air-conditioning and heating cycles when the building is complete can also be problematic.
Choosing the right timber species often comes down to a number of factors. According to Barnes, things to consider when it comes to flooring are the colour and aesthetics, traffic flow and what type of project it will be used in. When it comes to structural use, codes and regulations often take on more importance, such as BCA and Australian Standards requirements for strength, durability and bush fire ratings.
Barnes says there are five key steps designers can take to ensure the successful use of timber. These include:
1.Establishing the usage application and working backwards.
2. Selecting a species. As well as the aesthetic, other factors such as the aspect or traffic that the timber will be exposed to will to determine the most suitable species and finishing.
3.Informing the client. Relationships can be tested when the picture in a client's head does not match the end result. Explaining the natural colour and feature variations that occur within timber products can help prepare clients for the final outcome.
4.Being aware of the variety of product options. Finding the right solution for a particular design is broader than purely species selection. For example, the type of subfloor that a timber floor will be laid over will have an affect on the type of timber flooring product that can be used. 5.Considering sustainability.
With over 40 major timber species across six to seven major products groups, it can be easy to see why the material can be so easily misused. Mitchell advises specifying timber according to the relevant Australian Standard. For example, AS 2796.1-1999 defines the various properties for the specification of sawn and milled hardwood for flooring and cladding. "For structural applications, the best and most common timber species are the softwoods radiata pine and Douglas fir (or Oregon). We are also seeing increased volumes of some great imported softwoods, such as various spruces and Baltic pines from Europe and North America due to the high Australian dollar," Mitchell says.
"The use of engineered timber products such as I-beams, laminated veneer lumber (LVL), plywood box beams and glulam is also really taking off.
"The most common mistake made with structural timber is not realising the increased span these new engineered timbers can give. Specifiers also need to be conscious of the correct hazard level for a given application."
Specifiers have ample resources available to guide them. For example, the Timber Development Association in NSW and the ACT have on-site technical CPD presentations on specification, designing for durability and finishes and coatings.
Carter Holt Harvey has a software program called designIT for the design of engineered woodproducts to aid with the selection of beam sizes. "The early specification stage is suited for the supplier to work with the architect as their idea is formed when they know what they want to achieve. Discuss the product's fit to your vision," Sherry says.
Boral Timber also has dedicated specification managers who can advise architects and building designers on their options for structural and aesthetic timber use.
"The opportunity to use timber in creative ways far exceeds its limitations. We have seen our structural F27 grade hardwood used to design a bespoke benchtop in a commercial setting and our standard decking product used to make decorative screens in an outdoor residential space," Barnes says.
"Once you explore the breadth of Australian hardwood species available, you will be surprised at the flexibility timber can afford a building design.
"Once the initial concept is formulated, a specification professional within the supply source can save architects and designers a lot of research time by directing them to the most suitable product options."
