Could you advise what would satisfy this clause in AS1684? - 7.2.3: Where ceiling battens are used, the size and fixings shall be appropriate for the mass of the ceiling material used, to provide a flat finish to the ceiling. The standard specifies batten sizes based off 12kg/m2 but does not specify a connection. Would a nailed connection suffice or would it have to be screwed?
AS1684 is specific on ceiling batten sizes but, as you say, doesn't specify how to fasten them. If the ceiling battens are part of a trussed roof system, providing bottom chord restraint, the truss company should be able to provide connection details. Installation guides for products such as Gyprock assume the plasterboard will be direct-fixed to the underside of ceiling joist or trusses, in which case the plasterboard has the same restraining effect as ceiling battens at 600mm centres. Unfortunately we have no other data on fixing ceiling battens, but no doubt a consulting engineer could advise.
There is no standard time limit on the allowable weather exposure of timber framing. Perhaps moisture content has exceeded 20% for periods of time, with periods of drying in between, since it would be unusual to record such high levels of moisture for a continuous 12 month period. It might also be the case that the high moisture levels are only present in surface layers, rather than throughout the depth of the timber. In any event, there is not necessarily any harm done by a prolonged period of 20% moisture content. Loss of structural integrity (decay) can be checked by probing with an instrument such as a screwdriver, paying particular attention to joints. This topic is explained in more detail in our Technical Design Guide no. 12 titled Impact and Assessment of Moisture-affected, Timber-framed Construction. A copy can be downloaded from our website via this link https://www.woodsolutions.com.au/publications. If there are any glued products such as LVL’s on site, these are made with a Type A water-resistant glue bond as used in Marine Grade plywood. However the producers of such products may have their own recommendations on weather exposure.
New Guinea Rosewood is relatively durable outdoors, rated Class 2 above ground according to Australian Standard 5604, Timber – Natural durability ratings. This implies a probable service life of 15 to 40 years. The upper limit of 40 years depends on the timber being subject only to ‘periodic moderate wetting’, with adequate ventilation and drainage, while a lower service life would apply if wet for prolonged periods, eg. weather-exposed in a tropical or sub-tropical climate. Rosewood has a lower hardness rating (4.7 kN) than most Australian hardwoods but is slightly harder than pine. Blackbutt is rated Class 1 above ground with a probable service life greater than 40 years and a hardness rating of 8.9 kN. The hardness rating refers to the force required to make a standard size indentation in the surface.
