Timber Reports/Advice

  • Timber Inspection compiles reports on a wide range of timber issues. The most common being issues with timber flooring usually because of expansion and contraction. Timber exposed to the weather that has decayed quicker than what it should have is probably the second most common. We have noticed low durability imported timber products coming onto the market recently and we would expect decay issues to overtake flooring issues in the next few years.
  • When carrying out investigations and writing reports we abide by the expert witness code of conduct.
  • To avoid the need to use our services below are some simple issues you should consider:

Timber durability

  • Timber durability ratings include the heartwood only. If timber contains sapwood (the outer layer of timber just below the bark, usually lighter in colour) and the timber is subject to the ingress of moisture the sapwood will decay fairly quickly. Sapwood inside should not be a concern provided any lyctid susceptible sapwood has been removed or treated.
  • If the timber is used in contact with the ground or in-ground it should be in-ground durability class 1 or 2 or treated to H4 or H5. H4 is for soils that are wet periodically and H5 is for extremely wet or saturated situation or timber which is structural and difficult to replace.
  • If the timber is used above the ground but subject to the ingress of moisture than it should beabove-ground durability class 1 or treated to H3 or above.
  • Make sure the durability rating given for a species is to Australian Standards. Durability ratings used in other countries vary considerably. In some countries their durability 1 expected life is not much better than our durability 4. There are a lot of overseas species listed in the Australian durability standards. If you cannot verify the durability of a species do not use it in an exposed situation.

Treated Timber

  • Did you know that treated timber is not necessarily treated all the way through. The H3, H4 and H5 hazard levels for solid timber only require that all the sapwood be treated and that if heartwood is present than any heartwood within a given distance from the surface also be treated. This distance depends on the timbers natural durability, the hazard level and the size of the timber.
  • When using treated timber in exposed situations the structure should be designed so that the timber is butted together rather than mortised. This prevents the treated envelope from being damaged. Try to avoid cutting treated timber. Should any cutting or drilling be required reseal the cut end or drill hole with an appropriate chemical reseal product. Try to protect cut ends. For example if you cut joists to length place the cut end under the eave.
  • Many softwoods do have a high sapwood proportion so a reasonable number of timber pieces may be all sapwood therefore being treated all the way through.
  • The Timber Inspection Branch of Forests NSW used to administer the NSW Timber Marketing Act which was repealed on 1 January 2013. To sell treated timber into NSW you needed to have your treatment plant registered. Mr Forrester Managed the Timber Inspection Branch. He and his inspectors, who now work for this company, carried out random sampling at retailers and on building sites. A timber treatment company’s registration could be suspended or cancelled if they failed to comply with the Australian Standards 1604 treated timber series. Today consumer protection relies on the Building Code of Australia. If not a building and the timber is not fit for purpose consumers need to pursue this through normal legal channels or the department of Fair Trading.
  • Some of the chemicals used to treat timber are colourless.
  • To comply with Australian Standards, the timber must be branded except for:

– timber less than 500mm in length (E.G roll packs of garden edging) or;
– timber with a cross section less than 1500mm (E.G palings). Note decking must be branded regardless of size.

  • Other than those sizes avoid buying timber that has no brand.
  • The brand will be for example XXX 01 H3. XXX represents the treatment plant, 01 the chemical used and H3 the hazard level for which the timber can be used. O1 and 02 are chemical numbers for Copper Chrome and Arsenic (CCA). CCA cannot be used where regular human contact may occur such as decking, handrails, seating, playground equipment etc.
  • Most methods for treating timber requires the timber to be dry prior to treatment. Treatment processes, usually designed by the chemical manufacturer often in conjunction with scientists, need also to be used. Unfortunately some timber treaters may take short cuts to try and gain a commercial advantage over their competitors. Of the testing we have done where timber failed prematurely none met the requirements of the Australian Standard.
  • It is recommended when buying treated timber to choose timber treated by a member of the Timber Preservers Association of Australia whose code of conduct requires treatment to the standards. Treaters who demonstrate that they have an independent audit processes in place may also be considered.
  • If any timber retail outlets would like an audit of their stocks to ensure the timber is correctly treated, please contact us.
  • If any consumers require a report on any treated timber they have bought please contact us. Additional information can be found at www.tpaa.com.au (Timber Preservers Association of Australia).

Moisture Related Issues

  • Timber is hydroscopic. It takes up and loses moisture from the environment whether inside or outside. If the air is humid timber absorbs moisture and if the air is dry timber loses moisture.
  • Timber expands as it absorbs moisture and shrinks when it loses moisture. Most of the size, gain, or loss, is at right angles to the direction of the grain or in the case of most floorboards an increase or decrease in cover width. The change to the length of a board is usually no noticeable. We have however seen some length changes in pine decking. In our opinion this is because pine can be knotty with the grain distorting around these knots therefore expansion across this distorted grain leads to an increase or reduction in length. Pine also absorbs moisture readily and during rain will often close up a 5mm gap left between boards.
  • Because of this expansion, floorboards when being fitted have to have a 10mm gap parallel with the length of the boards on either side of the room (along the walls). Where the floor width at right angles to the length of the floorboards exceeds 6 metres a further 10mm intermediate expansion gap is needed for every additional 6m of floor width. These intermediate expansion gaps can be distributed evenly across the floor or many smaller gaps can be left of an equivalent value. The expansion gaps are to accommodate slight changes in moisture content after a floor has been laid or to allow for expansion should the environment change. The average moisture content of timber protected from the weather in the Sydney region is documented as 12%. Most reading we take are around 11%. Moisture content of timber inside different individual buildings will change. Timber in buildings close to bodies of water or at the bottom of a valley may have higher moisture contents than timber in buildings on top of a hill.
  • Houses that have damp subfloors usually vary more than those that don’t between wet and dry seasons. If a house has a damp subfloor you may consider better drainage and/or increased ventilation.
  • When laying floorboards in existing buildings it is good practice to check the moisture content of any existing boards to see if the moisture is close to the same level as the new floorboards that are to be laid. If the moisture content of existing boards are high then you may wish to consider changing the environment before laying. If the moisture content of existing boards are lower you may need to acclimatize for a while.
  • If your floor layer does not have a moisture meter they should get one and learn how to use it. Adjustments to the meter readings are usually required due to species, and temp. Electrical resistance meters, at moisture contents below 20%, are usually accurate to plus or minus 1%. Pad meter are not in our opinion as accurate.
  • If you are replacing floorboards because the original floorboards or bearers and joists have decayed, then the environment will need to be improved before new floorboards can be laid. Timber will decay if its moisture content is around 20% or greater for extended periods.
  • If floorboards were laid with a moisture content of around 11% and the floorboards then took up moisture and the floorboards became around 20% this would cause massive expansion of the floorboards.
  • Cupping is caused because of changes in moisture between the top surface and the bottom surface. One surface is shrinking and/or expanding at a different rate than the other surface.
  • In general, most floors are laid with no issues arising.
  • It is important to have realistic expectations about how timber performs. If you have a large areas of glass that allow direct sunlight on a timber floor for extended periods, then some shrinkage and or cupping may occur. This may not bother some people but others may consider it a defect.
  • If you lay timber decking in direct sunlight some slight cupping should be expected. The wider the boards are, whether they are decking or floor boards the worse the effect.
  • If you are a buyer or seller and need a report or assistance, please contact us.