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Question

I noticed in the BAL FZ you have 15mm ply. Can you use any type of 15 mm ply on top of the trusses and rafters?

Woodsolutions Answer

The metal sheet roof system for BAL-FZ (Flame Zone), assessed by Warringtonfire, was based on 15mm pine plywood or 15mm OSB roof lining. 

Answered on :
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.
Question

Just wondering if cut stringers are allowable under the BCA and if so where can I locate the relevant span tables for stringers and treads in mgp10 treated pine.

Woodsolutions Answer

Our Technical Design Guide #08 includes span tables for stringers and stair treads. A copy can be downloaded free of charge from our website via this link https://www.woodsolutions.com.au/publications. Alternatively, a hard copy can be purchased here https://www.intertekinform.com/en-au/search/standard/?searchTerm=WS08&productFamily=STANDARD&q=WS08. Note that the Guide refers to F5 grade treated pine rather than MGP10 since much of the treated pine in the marketplace is graded F5 or F7.

Answered on :
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.
Question
I am framing an eave overhang of 600mm to the side of a skillion roof. The rafters on the roof are spaced at 600 centres. The code says a) the fly rafters can be supported on cantilevered beams etc, or b) you can use outriggers. For clean lines I'm using out riggers, i.e. no supporting beams. The code then says 'members' require a backspan of twice the overhang. My question is - are my outriggers of the same section size as all other rafters (190x45) classified as 'members'? and are they also required to backspan two thirds? (1200) And while there is no mention of it at 7.2.25.1 , is it specified elsewhere that a secondary rafter is required along side the rafter supporting the backspans?
Woodsolutions Answer

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.

Answered on :
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.
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