Target Design Life: What it Means to You

If you are looking for timber suppliers in Brisbane, it is probably because you are getting ready to build a great project. Whether you are a construction professional getting ready to build a house or a homeowner looking for timber flooring for your Brisbane home, there is a little-known concept in the timber industry that is very important to you: target design life.

Target design life is defined by the Queensland Government as the “anticipated satisfactory service life” of timber when the timber is used in accordance with “good building practice” and the regulations set forth by the Australian Standards and the Queensland construction specifications.

Target Design Life - Timbers

Queensland has a long history of using timber as the preferred material in a host of assorted construction applications. However, every single home has a lot of different components and they don’t all have the same design life expectancy. In other words, it is well-known while the house is being constructed that some components are going to last longer than others.

Some components will be expected to last as long as the structure does, while others are expected to eventually break down and need replacement.

A lot of factors come into play, such as the ease of access for maintenance, the projected cost of labour and materials for assembly and the propensity on the part of homeowners to change certain aspects of their homes due to fashion changes.

This means that some components of a home may only be expected to provide satisfactory performance for up to five years, such as fence palings or battens. Other “permanent” structures, such as house stumps and roof trusses, may be expected to last for fifty years.

Consequently, there are three target design life categories in Queensland: 5 years, 15 years and 50 years.

Classifications and Regulations

In the construction specifications, timbers are classified according to applications in schedules A, B and C. They apply to Class 1 buildings such as houses and Class 10 buildings such as garages, carports and sheds. The classification of the timbers is only valid when good practices are followed for design, construction and maintenance, especially when managing moisture by making sure there is adequate ventilation and avoiding damp situations.

Damp situations are usually caused by preventable deficiencies. These include: designs that trap water, inadequate damp-proofing such as faulty flashing or sarking, faulty external wall framing and faulty roofing. Filling sub-floor cavities, called “plugging,” using insulation that retains moisture or design that inhibits the free movement of air through walls, vents and sub-floor cavities can all cause damp situations.

When the applications are in-ground or exposed to weather hazard, they are classified into decay hazard zones. These zones are described in the Timber service life design guide.

Above Ground Decay Hazard Zones

In climates such as Brisbane and really all of Queensland, the performance and serviceability of construction timbers is constantly under attack by the environment. Due to high heat and high humidity, timber in Brisbane is extremely susceptible to fungal attack. The document/guide Construction Timbers in Queensland classifies each local government area into a ground decay hazard zone.

The ratings are from Ag:A to Ag: D, with Ag:A having the highest likelihood of above-ground decay and Ag:D having the lowest.

In Ground Decay Hazard Zones

The likelihood of decay is greater for timber that is placed in the ground than that which is installed above ground. The ratings are just like those for above ground, but with “Ig” instead of “Ag.” In other words, “Ig:A” has the lowest potential for in ground decay while “Ig:D” has the lowest potential.

What it Means to You

At Narangba Timbers, we have been the most trusted timber suppliers in Brisbane since 1972. Our customer service staff is among the most knowledgeable you will ever talk to. Call us when you are planning a project, large or small. We can make sure that you use the correct timber for your project.

We know it takes a lot of work to complete a timber deck or install timber flooring and we want yours to last a long time.

Call (07) 3888 1293 to learn more.

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Posted in Jack's Blog, Timber Regulations, Timber Suppliers Brisbane