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Changes to the Timber Framing Code

The NCC 2022 will bring in to affect the updated AS 1684.2:2021 and AS 1684.3:2021 timber framing code changes, here is what you need to know on the updates.

As part of the raft of changes in NCC2022 some of the reference standards have been reviewed. 

One such standard is the Timber Framing Code (AS1684 Part 2 and Part 3) which has undergone a detailed review and as a result there have been a number of changes to this standards. 

While fundamentally the document has not changed, there are some subtle but significant changes which it is important to familarise yourself with to ensure compliance when using these standards and undertaking timber framing in accordance with AS 1684. 

The changes that occur in both AS 1684 Part 2 and Part 3 documents mirror each other so for the purposes of the below information what is true for one is true for both. 

AS 1684.4 (simplified) has not been updated at this stage to reflect the corresponding changes in Parts 2 and 3.

New and clarified definitions

The standard has moved the definitions into a new section 1.3 of the code and expanded upon this section by adding new defined terms for coupled and non-coupled roofs as well as reworking the existing definition of roof load widths to add clarity.

Updates to reflect contemporary industry practice

There have been several change which have been introduced to reflect industry practice and products available.

As such the standard has increased the allowable size of decking boards, provided construction details for 45mm roof battens and it also now includes new connection details for rafter and truss tiedowns as well as floor joists to bearers or top plates. 

Changes to bracing

One of the more significant technical changes, is that the standard now applies an assumed Joint Group Strength of J5 or JD5 (Previously a J4) this reflects the products coming to market. 

The effect of this changes results in reduced capacity for many plywood and hardwood bracings designs and care should be taken when preparing a bracing plan or design to ensure you are applying the current bracing value. Noting that this also effects fixing of bottom bracing walls  

When using these updated bracing tables this change will result in you requiring either a greater amount of bracing in the building or for you to increase the capacity of the bracing to make up for the reduction in kN/m values.

Formatting and readability

As a part of the modernization of the Australian Standards when standards are updated, they need to be compatible for use in both printed and electronic format (that can be accessed across a number of devices). 

If you are accessing the standards in the electronic format, you will notice hyperlinks throughout the document which when clicked on will take you to the nominated, clause, table or figure. 

As part of an ongoing project Standards Australia aim to improve readability of their documentation. As a result, a number of clauses have been simplified, expanded upon or rearranged to add clarity to what is required and to make the document easier to read.

Moisture Content and Shrinkage 

Appendix E the Informative section of the standard covering moisture content and shrinkage has been greatly expanded upon to provide a more comprehensive guidance on the effects of temperature and humidity on timber performance. 

Want to know more

For further information on the change to the timber framing code (AS 1684.2:2021 and AS 1684.3:2021) refer to HIA’s summary of changes document.

To find out more, contact HIA's Building Services team.

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