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How is the durability of the timber rated?

The durability rating system is a classification based on in-ground and above-ground applications, as listed in AS 5604-2005 (Timber Natural Durability Ratings). 

The system is a guide to the correct selection of timber for any application – so you are aware of the expected length of time that it will do the job.

Class 1 is the highest rating and Class 4 the lowest. Durability Class relates to heartwood deterioration, due to fungi, termites or other hazards and are rated giving expected “lifespans” for above and in-ground contact conditions.

The sapwood of all species is non-durable unless treated. Treatment of timbers improves performance.

*the Standard (AS 5604-2005) describes how these were derived.

To learn more about heartwood and sapwood go to: WoodSolutions

How does the MGP rating compare with the F grade rating in timber?

MGP stands for Machine Graded Pine, specifically used for grading structural pine. Three grades are currently available, being MGP 10, MGP 12 and MGP 15.

MGP can be substituted for F grade pine as follows:

MGP 10 for F5

MGP 12 for F8

MGP 15 for F11

This is a one-way substitution. F graded material cannot be substituted for MGP.

The 2007 edition of the Pocket Span Table Book, produced by WPV and based on design information in AS 1684 Part 2, makes it easy to determine what timber size is required for a range of residential timber framed construction applications. See the design manuals page for details

What are some alternatives to Merbau for external timber decking?

As Merbau is a rainforest species from Asia, the sustainability of supply cannot always be assured. You may wish to consider alternatives to this and other imported timbers when it cannot be proved where they come from.

Treated pine is an obvious choice for a low-cost, easy to use decking material. Use a non-arsenic-impregnated treated wood such as LOSP or ACQ on decking boards and handrails. Traditional CCA treated timbers can still be used for the structural deck components (bearers and joists) and give consistent performance.

Composite wood products, made from a pulp of wood flour and plastics are another option that has about 20% of the decking market in the USA now. Over 90% of the composite wood’s materials are recycled or reclaimed. Some see it as an environmental option because it uses waste products and they view it as being more sustainable in terms of total embodied energy if manufactured in Australia from materials sourced here.

Victorian hardwoods achieving Durability Class 1 and 2 are produced as decking.

These species are:

  • Grey Box
  • Red Ironbark
  • Silvertop Ash
  • Sugar Gum
  • Yellow Box
  • Yellow Stringybark

It is important to know if the timber is being supplied as green, air dried or seasoned and to make adjustments accordingly for its installation. Timbers which have a very high moisture content may not readily accept surface treatments and shrinkage could be a problem.

Should I acclimatise my floorboards prior to installation?

Acclimatisation of floor boards is advisable when installing in seasonal extremes of weather, experienced during summer or winter. The moisture content of the floor boards should always be checked with a moisture meter prior to installation.

Generally for Melbourne; floor boards reach an equilibrium moisture content of between 10 to 12%. If it is outside this range, acclimatisation will be necessary. This must be in the closed internal room conditions, so that the boards can reach their appropriate moisture level. This is achieved by storing the boards in the room they are to be installed for at least 3 weeks. When stacking, ensure that there are spacers in between for air flow to all sides. The moisture content then needs to be checked again, prior to installation.

The floor boards should be delivered once the building is at lock-up stage so that they can be correctly stored, in the environment in which they will be installed. It is fruitless to store the boards in a garage or in a location that will cause them to take up moisture. If the floor boards arrive on site between 10-12% in a traditional residential application, and the house is completely sealed to the external environment, then the boards can be laid immediately.

For air-conditioned environments it is advisable to acclimatise the boards with the air-conditioning system running, as they will generally need to be installed at a lower moisture content than for traditional residential environments, as internal air conditions are generally drier.

What are hazard classes for treated timber?

Hazard classes rate the environmental hazards to which treated timber can be exposed. For instance, if the timber is to be placed in-ground it will be exposed to severe decay, therefore timber will need to be treated to H2 level.

For more information visit Timber Preservers Association of Australia.

How does timber sub-floor construction meet 6 star energy rating in Victoria?

There are a number of options that can be used to meet 6 star operational energy requirements.

Smart design of windows and their placement and size, increasing insulation in walls and ceilings, site orientation and choice of materials, selective double-glazing and enclosing the sub-floor space will all improve the 6 Star Energy rating. The adoption of First Rate 5 by the Victorian Government has seen suspended timber floors rating improved by 0.5 to 0.75 of a Star, with improvements to the design engine software (from NatHERS to AccuRate).

Do we really need timber from native forests?

Just take a minute to think how much you actually use timber.

The house you live in is more than likely framed with both plantation and engineered pine and high strength Australian hardwood (native forest) products. To really make your house a home, you probably have some timber-framed windows and timber doors. You may have a hardwood feature polished floor (or two); a crafted hardwood kitchen, entertainment cabinet, bathroom unit or mouldings; or some quality hardwood furniture: tables, chairs, sideboards, etc. Then there are more rudimentary products made from the rest of the tree: pergolas, decks, picket and paling fences, garden chips plus all your high quality paper products.

It’s probably a surprise to you just how many hardwood products you do in fact use. And not only are they sourced from responsibly managed government-owned forests, each article of wood stores carbon that has been sequestered as the tree grows.

Rest assured that Victorian hardwood products are grown and harvested from government-managed forests in accordance with world-class principles for ecologically sustainable forest management.

The government makes available around 15% of the Victorian forest resource as an ‘industry area’ from which the products we as consumers demand can be drawn. Of this area, very little, only 1% in any one year, is harvested. This is totally re-generated with at least a one for one replacement ratio.

Areas where timber can be taken are clearly differentiated from the remaining 85% of Victoria’s forests which are managed by the Government as state parks, reserves, water catchment areas, etc. – no timber is taken from these areas.

Does Victoria really have sustainable forest management practices?

Victoria has one of the highest forest reservation rates in the world – well above international benchmarks set by the International Union for the Conservation of Nature and the World Wide Fund for Nature. Victoria also has very responsible forest management practices.

The sustainability of our native forests are not at risk as every hectare that is harvested is regenerated. Victoria provides a shining example for the rest of the world to follow. We really are the world’s University of Sustainable Forest Management.

For more information visit VAFI.

What are woodchips and why do we need them?

When harvesting a tree it is important that we maximise its usage.

Not all the wood can be used as sawlog and solid product. Rather than leave or burn residue, today it is ‘chipped’ into tiny pieces, about the size of a 50 cent piece. These wood-chips are used to create the pulp that is needed to make paper.

Both softwood and hardwood woodchips are used for many types of paper products including: newspapers, magazines, computer paper, printing feedstock, packaging and tissues.

They are also used to make building board and processed into rayon for clothing.

If you want to make good quality writing paper, or paper for magazines and posters, you need to use woodchips that come from eucalypts, or other hardwoods. Hardwoods have shorter, smaller fibres and make papers with a better surface for printing.

Paper made from woodchips that come from pine trees are better for making newspaper, tissues and cardboard. Softwood fibres are longer and make paper with a higher tearing strength.

Woodchips can also be used as a garden mulch, to conserve water and keep down weeds. After a while, the chips decompose, adding nutrients to the soil.

Is timber sub-floor construction a sustainable option under 6 star energy rating?

While the timber industry strongly supports sustainability-based regulations, it cautions that these need to be rational and holistic, not inconsistent, inflexible and narrowly focussed. The timber industry has provided a number of examples of how the current software discrimination of sub-floors is counter-productive to the government’s goals. Extension of the transition period for timber floor construction in Victoria will give time for further research and updates to the 6 star design software.

The concept of energy regulations was promoted to government by the Sustainable Energy Authority Victoria (SEAV, now Sustainability Victoria) and was based on a concept of CO2 reduction. Figures used were an “annual reduction in greenhouse gas emissions of 37,000 tonnes, equivalent to removing 10,000 cars off the road a year.”

Recent research has shown that utilising a concrete slab on ground, in preference to a timber sub-floor, produces a net increase in CO2 emission of 15 tonnes* per home. This means that if builders move from sub floors to slabs, presuming they are a cheaper option, more CO2 is in fact released to the atmosphere (this equates to around 37.5 years of operational energy usage before the home begins to provide any net environmental benefit).

* State Forests of NSW – BHP LISA Model

If we looked at this another way, and the government decided to ban concrete slabs, based on 36,600 new homes constructed in Victoria (2003/04 figures), this alone would result in a massive saving of around 550,000 tonnes of CO2 per year. Five star energy ratings only consider the amount of heating and cooling that will be required to keep the home comfortable for the occupants. This is only one part of the sustainability equation.

Another key factor is the embodied energy of the materials used to construct and maintain the home. Research undertaken for the Victorian Building Commission showed that over a 50 year building lifetime, a brick veneer home built using a suspended timber floor used less total energy (operational and embodied) than the same home built on a concrete slab.

Our house plans show I-Joists for roof and flooring beams. What are they?

I-Joists are engineered timber beams manufactured in the shape of a capital “I” from ply, timber sections, LVL (Laminated Veneer Lumber) etc. Engineered timbers used for I joists have the following advantages:

  • They give the same performance as a solid timber beam but are lighter to install (saving time and therefore money, and being easier on builders’ backs)
  • Engineered timber products generally utilise more of each log, giving better return from this valuable resource
  • The strength is enhanced, meaning a softwood, or lower-performance timber can be used in an engineered timber application to increase capacity. Making, for instance, better use of plantation timbers
  • As an engineered product, they are available in longer (and standardised) lengths
  • It is easy to install services by creating holes in the webbing section of the joist

Currently AS 1684, which gives guidance to residential building with timber construction, does not include engineered timber products. You can check with individual manufacturers or suppliers for their span tables which have design specifications to give as good, and sometimes better, performance.

Visit Engineered Wood Products Association of Australasia for more general information, manuals and research reports on ply, webbed and engineered timber products including how to ensure the products used are from sustainable sources and safe in many applications.