We assume the outriggers will be supported on the external wall. Note that they will need to be adequately tied down to the wall, and to the supporting rafter, given they will be within 1200 mm of the edge of the roof. Clause 7.2.25.1 of AS 1684 states that the cantilevered outriggers ('members' in this case) shall not project beyond their supports by more than 25% of the allowable span of the member. Your 190x45 MGP10 rafters at 600 mm centres have a single span of 4900 mm, with 40 kg/m² roof load (Table 29, N2 wind classification). A cantilever of 25% = 1225 mm, so a 600 mm cantilever is well within the limit. The backspan is 2 x 600 = 1200mm. There isn’t a specific requirement for a secondary rafter alongside the rafter supporting the backspans. However, you will be removing a rafter to insert the outriggers, so you need to ensure that the first rafter supporting the backspans can support the (approx.) 1200 mm wide roof load. So we recommend checking to see if the common rafters can still do the required span if spaced at 1200 mm. If they can’t, then a secondary rafter is advisable. Our calculations assume steel roofing with ceiling lining on the underside, but you can recalculate for other combinations of roof cladding and ceiling lining.
Warringtonfire’s Regulatory Information Report 45980.10 confirms that hoop pine and radiata pine 9mm thick or greater fall into Group 3. A copy can be downloaded from our website via this link https://www.woodsolutions.com.au/resources/standards-codes/fire-test-reports. Although originally to expire on 31 December 2023, RIR 45980.10 has been extended to 31 December 2025. Slash pine is not specifically mentioned, but since all timbers so far tested fall into Group 3 it’s highly likely that slash pine would also be a Group 3 material.
I have a class 2 building with rise in storeys of 3. There is a class 7a car park on the lowest level used exclusively for parking. NCC2022 C2D13 Fire-protected timber: Concession / NCC 2019 C1.13 Fire-protected timber: Concession, requires a sprinkler system. I understood that sprinklers are not required up to 3 storeys as per the NCC 2019 changes and WoodSolutions Timber-Framed Construction for Multi-Residential Buildings Class 2 & 3 (2022 version). I can't seem to find an NCC clause that confirms this concession (permitting no sprinklers). Does it exist?
Sprinklers are not essential but without sprinklers, according to NCC 2022 clause S5C20 (2), the carpark in the lowest storey and the floor between it and the Class 2 part above would have to be of concrete or masonry. So the lowest storey is virtually a concrete/masonry box with the timber-framed Class 2 occupancies on top.
