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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. Please can you tell me the material group that Baltic pine falls into under the fire hazard indices?

Baltic pine has been tested and falls into Material Group 3 with an average extinction area less than 250m²/kg. This applies to Baltic pine wall and ceiling linings with a minimum thickness of 12mm.

Q. Can you please give me details of suppliers of certified fire retardant products?

There are fire retardant products that claim compliance with Australian Standard 3959-2009, "Construction of Buildings in Bushfire-Prone Areas", for building sites up to and including BAL-29. An example is the Cease Fire Timber Fire Retardant System. This is a four-stage paint system consisting of a primer, intumescent fire retardant coat, clear sealer and top coat. You can find out more from Prudential Coatings, phone (07) 3129 5147. Other systems may also be available if you search the net. Note that we have not independently verified such claims, nor scrutinised test reports.

Q. More info needed on intumescent paint and certification for complying with BAL 12.5.

BAL 12.5 applies to low risk areas and is primarily concerned with protection from ember attack. Where "bushfire-resisting" timber is required (eg. external wall cladding, timber window joinery, etc, that is less than 400mm above ground or an adjacent deck) a fire-retardant coating is deemed to make any timber "bushfire-resisting", as long as the coating satisfies the test criteria in Australian Standard 3959-2009. Note that in BAL 12.5 timbers of certain density also comply without a fire-retardant coating.

Q. AUS 90mm x 45mm KDHW handrail bal 12.5 - 19 options - central victoria

There are no restrictions on balustrades, handrails and other barriers in BAL-12.5 or BAL-19. It's only at BAL-29 level that restrictions on handrails cut in. So you only need to consider durability requirements, assuming the handrail is exposed to the weather.

Q. I am deliberating on a dilemma where a contractor has not allowed for treated timber in a refurbishment project I am managing. The design had a full specification and this speaks of timber durability and treatment levels as described in the standards. My question is if I have covered ant caps and a barrier treatment in the refurbishment is there a mandatory obligation to provide H1 or H2 level timbers in the construction works. I was under the impression that industry standard was to use treated timbers regardless.

It's not mandatory under the Building Code of Australia (BCA) to use H1 or H2 treated timber. However, a written specification that calls for H1 or H2 timber is a contractual document and the client would have to agree to vary it. What is mandatory under the BCA is to provide termite barriers in termite risk areas, if the primary building elements (ie. structural components) are at risk of termite attack. H2 treated timber is not at risk of attack and therefore, technically, barier systems are not required when H2 treated timber is used. However, the timber industry recommends installing barrier systems even when H2 timber is used, otherwise termites can enter the building and attack the contents, although the structure is protected.

Q. Technical information on Vertical Timber cladding * Suggested suitable timbers, cladding, product minimal maintenance * Suggested window and door sealing for Vertical timber cladding * Timber wall frame specifications for Timber wall frame and vertical cladding for walls 3900 high *

A useful reference that will answer most of your questions about cladding is Datafile FP1 from the NAFI Timber Manual. The manual is now out of print but the Datafile is available on the net via this link: http://aussie.designpine.com/Files/HintsAndTips/Revised%20Datafile%20FP1%2072dpi_0_4841.pdf. Although the Datafile was last revised in 2004 not much has changed regarding installation details, suitable timbers, etc. For wall frames 3900 high you will need to consult an engineer. A User Guide is available to extend the wall heights in AS 1684 to a height of 3600, available from the Wood Solutions website at http://www.woodsolutions.com.au/Articles/Resources/AS1684-external-wall-heights. However, it doesn't extend to 3900. If you are referring to the User Guide, note that reference to bracing wall heights up to 4800 relates only to internal bracing walls in houses with cathedral ceilings, and can't be applied to external wall frames.

Q. Wanting to find some AS/NZS fire classifications for a Western Red Cedar Roof constructed - either shingles or 16mm shakes.

We are not aware of any fire rating under Australian/New Zealand Standards for western red cedar shingles or shakes. Figures quoted on the net usually relate to US and Canadian regulations. On the other hand we are not aware of any restrictions on the use of wooden shingles and shakes on single occupancy detached dwellings unless they happen to be in a bushfire-prone area, in which case roof coverings in Bushfire Attack Level (BAL) 12.5 and above have to be non-combustible.

Q. We are structural engineers and been asked to load test a timber balustrade. Do you have any computer programmes that will do this?

We don't have a programme that would record data during load testing. This is a service that a NATA-accredited laboratory should be able to provide, following the procedure outlined in Appendix D to AS 1720.1-2010. Alternatively, one of the Technical Guides in the Wood Solutions series includes balustrade designs that comply with the loading provisions of AS 1170.1, and therefore satisfy the BCA. The guide is number 8 in a series of technical publications which can be downloaded from the Wood Solutions website at http://www.woodsolutions.com.au/Resources/Design-Construction-Guides.

Q. I am an architect currently documenting a timber frame multi-unit single storey class 1a developement. The PCA has advised that your details contained in your design and construction guide for Town house buildings Class 1A do not meet the DTS provisions of the BCA. Specifically with regard to using timber blocking to acheive the required fire separation at the junction of separating walls to external non fire rated timber frame walls clad in FC. However your guide Page 4 states that your details are DTS. Can you please confirm that using 90 x 45 radiata pine blocking meets the DTS provisions of the BCA with requiring an Alternative Solution. I need to resolve this with a degree of urgency and would much appreciate your prompt response.

Timber Design Guide 06 titled "Sacrificial Timber Construction Joint" explains how timber blocking can be used to maintain a particular Fire Resistance Level (FRL). The Guide can be downloaded from the Wood Solutions website at http://www.woodsolutions.com.au/Articles/Resources/Design-Construction-Guides. The Guide contains an Appendix which lists the test and assessment reports on which the Guide is based. As long as your design complies with the recommendations of Technical Guide 06 we consider it should satisfy the DTS requirements of the BCA.

Q. I am replacing a carport that has 190 by 45 hardwood beams which have a slight sag in them. The carport will be 6m by 6m and I want to use LVL beams, I have been told that 190 by 45 will span 6m with no sag. I wish to retain as much height as possible for clearance. Is this the best size and material. Derek

If the beam in question is the "pitching beam", ie. the beam that the rafters land on, it seems a bit undersize. However, it's difficult to give a definite answer since it depends on the design of the carport (trussed roof, pitched roof, skillion roof) and on how much load the beam is carrying. To determine the size of the new beam you need to have an accurate assessment of exactly how much load it is supporting. Various software programs are available on the net to calculate beam sizes and you can find the major ones on the Wood Solutions website via this link http://www.woodsolutions.com.au/Resources/span-tables-software-resources.

WoodSolutions

Did you know?

About 6% of Australia’s 147 million hectares of native forests are public forests potentially available for timber harvesting. Timber is harvested from about 1% of those public native forests each year.