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Ask an Expert

Building codes & compliance

Like to know what wood to use building a pergola or framing a barn? How about the difference between tung oil and polyurethane as a floor finish? How to revive decking or deal with merbau stains? Or how to meet the building code or bushfire standards? Or ask about the environmental advantages of wood or forest certification?

Q. Where can I get some hardwood visually stress graded in Adelaide?

We suggest you contact Timber Consulting in Adelaide on (08) 8373 5285. They have an experienced grader on their staff who can help you.

Q. I am restoring an old building with wooden framed windows. I have to fire rate the windows to 1 hour, is there a coating I can apply to the timber to give me the 1 hour fire rating?

No-Fire Technologies claim that "Nofire Intumescent Coatings have been tested by the CSIRO to AS 1530.4", but we were unable to find a copy of the test certificate on their website, or an indication of the Fire Resistance Level (FRL) achieved. If conducting your own search you will need to satisfy yourself that the products on the market do achieve a 1-hour FRL when tested to Australian Standards. You might also check that the need for a 1-hour fire rating is actually correct as it is fairly stringent. It is unlikely that windows in an old building contain glass that would resist fire for 1 hour, so even if you can find a suitable fire retardant coating, the windows will presumably have to be re-glazed.

Q. “Termite resistant primary elements are those that are specifically designed to take building loads” and, “no other termite risk management is required by the BCA”. I am trying to build accomodation for disabled in a very tight area. The very tight budget does not allow for any concrete floors. There is little room for Ramps. I need to build with only a 150mm bearer clearance. If I provide ant caps to the stumps, H2, H3 & H4 timber for all the building; can I justfy 150mm bearer clearance? Can I get a building permit in Broadmeadows Victoria?

We were not sure where your quote comes from. but it sums up the requirements of the BCA with regard to Class 1 and Class 10 buildings. If all primary building elements are treated to the required Hazard Level no other protection is required by the BCA. However, protection of the primary building elements does not necessarily stop termites entering the building and attacking items such as electric wiring, cupboard joinery, and other wood-based materials, it just means they won't attack the structure. Consequently we recommend including barrier systems (such as ant caps), so that the treated framing becomes a second line of defence rather than the only form of risk management. However, the difficulty you have with ant caps is that access is needed for inspection. Ant caps don't always stop termites from entering, they just slow them down and make their presence visible as they build up mud to negotiate their way around the caps. To provide access for inspection, a minimum clearance of 400mm is required between finished ground level and any structural components or other obstructions, eg. the underside of the floor bearers. If you are able to provide some other means of inspection, or some form of protection that doesn't require access, the ground clearance can be reduced to 150mm. The BCA also permits termite protection to be waived altogether if the building is in an area where termites are not known to present a potential risk, eg. in Tasmania and some parts of Victoria. We are not sure whether this applies to Broadmeadows but your local Council could advise.

Q. We are looking to specify a timber decking to an external pool area for a multi residential apartment development. Slip ratings are required for all of these wet areas. I am having trouble finding any sort of certifications or ratings (such as pendulum test) that are equivalent to those available for stone/tile floor finishes. Can you provide any information about species/finishes/treatments for slip resistance? Is there any way of certifying to an equivalent Australian Standard rating on a case by case basis?

We are not aware of any species of timber or profiled decking that has been tested for slip resistance to AS/NZS 4586 on a "bare wood" basis. Timber is a little different from tiles in that it usually has a coating applied in situ which would generally determine its slip resistance. However, we do know of a non-slip decking finish that has been shown to comply with AS/NZS 4586. A Sikkens Cetol system, marketed by Tenaru in Sydney, achieved a "W" classification under the wet pendulum test and therefore complies with the recommendation in Standards Australia's HB-197 for "swimming pool surrounds and communal shower rooms". For a technical data sheet, go to the Tenaru website at and select "Cetol Deck Plus" from the Products menu.

Q. Thank you for having such a clear and informative website. I am looking for information on Rosewood (Pterocarpus indicus) and I see that part of the Fire properties are incomplete. Would it be possible to give me the ignitability, flame-spread and smoke-developed figures?

We assume you are looking for these properties for a Class 2 to 9 building, to satisfy the requirements of Table 4 of the BCA's Specification C1.10. From that table the Flammability Index seems not to be required, but a Spread-of-Flame Index of 0 would not be achievable in any wood product unless treated with a fire retardant. It's possible that companies such as Worthington Industries might have suitable treatments. You can visit their website at this address:

Q. Regarding a carport design. I'm thinking of constructing a simple flat roof (0 pitch) carport, if I got rafters at 600mm spacing, would I require battens or it's not needed since my spacing is quite small?

We wouldn't recommend a completely flat roof, but it can be very low pitch. For example, Lysaght recommends a minimum 1° pitch for their Klip-Lok product and a 2° pitch for Spandek. However, you won't need battens or purlins if the rafters are at 600mm spacing - the roof cladding can be fixed direct to the rafters. For more details about fixing, see manufacturers' literature available on the net.

Q. I'm currently thinking of building a single car carport (flat roof) for my house, I just want to ask how do I figure out what the minimum size post would be? Does it depend on the weight of the roof sheeting + side beams?

Yes, the post size depends on the type of roof, the height of the post and the area that the post supports. If the carport is attached to the house, half the load is taken by the wall and the other half by the posts and side beam. Posts of 90 x 90 would generally be OK for a single carport attached one side, with sheet roofing and no ceiling. For example, treated pine posts of F5 grade, 3m high, can support up to 20m² of roof area.

Q. 1.What is the rate of Fire resistance for all glulam wood products? 2.How can we protect wood against Rain water? 3.Can we use gypsum boards as a protective layer in the wood products?

1. The fire resistance of glulam wood products depends on the density of the wood from which they are made. Australian Standard 1720 Part 4: "Fire resistance for structural adequacy of timber members" provides a calculation method to determine the effective residual section after a nominated period of exposure to fire. The American Wood Council has also published a detailed report on the subject, which can be downloaded via this link: 2. The protection of wood against rain depends on the type of wood. Species of low natural durability, such as pine, may need preservative treatment to protect them against wood rot and insect attack, while species of high natural durability such as ironbark will give long service without treatment. Protection against the surface erosion and hairline cracking caused by weathering is provided by surface coatings (paint, exterior wood stain, etc.)  3. Gypsum board can be used to protect timber members against fire, and the major plasterboard manufacturers all produce fire grade plasterboard, eg. Gyprock "Fyrchek" etc.

Q. I’ve been asked to supply material and labour to fire proof some timber beams on the underside of a large first floor decking. The builder has suggested firetard 120. I’ve researched a little this morning and there’s reason to believe this may not comply with the AS 3959 -1999 Can you please advise a product and supplier?

We understand that the test report issued by Firetard has been called into question. For more information paste this link into your browser: The difficulty site-applied treatments have in meeting the requirements of AS 3959 relates to the specified weathering test. Treatments are available that pass the fire retardancy test, but they are only suitable for external timber that is protected from the weather, for example by a verandah, pergola or wide eaves overhang. We are not aware of any site-applied treatments that pass the fire retardancy test AND the weathering test. Also note that AS 3959-1999 is superseded, and the current edition is AS 3959-2009. Having said that, we were not sure whether the application of a fire retardant was in order to comply with AS 3959, or whether it was intended as additional protection. Some types of timber are deemed to be equivalent to fire retardant treated timber on the basis of their natural fire resistance without any treatment at all. So depending on the type of timber used for the beams, and the Bushfire Attack Level (BAL) of the area where the building is located, the deck may already comply with AS 3959.

Q. Our structural report says the following comment, what does this mean? Coupled roof framing is required to have timber collar ties fitted to every second pair of opposing common rafters 5 collar ties are required above the living area and 3 collar ties are required above the bedroom area. Fasten as per Framing Code requirements. Do we need to comply with the above? Thanks and much appreciated.

The Framing Code referred to is Australian Standard 1684.2 which sets out how timber house frames are to be constructed (AS 1684.3 in cyclonic areas). A coupled roof is one where the lower ends of the rafters are tied together (or "coupled") by ceiling joists to stop them spreading apart. AS 1684.2 includes a diagram of a coupled roof (Fig. 7.1) showing the location of the collar ties. A collar tie is a piece of timber that provides extra rigidity to the rafters, tying them together at a point immediately above the underpurlins or, if underpurlins are not required, at a height above the top plate not greater than two-thirds of the rise of the roof. They are to be fitted to every second pair of rafters, or at 1200mm spacing, whichever is the lesser. Collar ties up to 4.2m long are to be fixed to the rafters with 3/75 x 3.05mm nails. Collar ties greater than 4.2m long are to be fixed with one M10 bolt. Further information, including diagrams, can be found in AS 1684.2.


Did you know?

In 2008 seventy percent of known old-growth trees are in nature conservation reserves.