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Question

I have been given some DA plans for a dual occupancy. The proposal is to raise an old timber and tin house and build in under, with one tenancy upstairs and one tenancy downstairs. The existing house would be supported on steel posts and beams. Is it possible to achieve the required fire ratings using timber framed, lightweight construction to the lower storey?

Woodsolutions Answer +

We take it you are the certifier so presumably you have classified it as a Class 2 building.It should be possible to achieve the required fire ratings for the external walls of the lower occupancy, but note that there will also need to be fire separation between the lower and upper occupancies, ie. a fire rated ceiling throughout the lower storey plus the required sound control. Also we believe the external walls of both occupancies will need the same treatment, not just the external wall of the lower occupancy. Our Technical Design Guide #02 may be helpful. It is available for download here: https://www.woodsolutions.com.au/publications.

Dual occupancy

Answered on 24-09-2020
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

Our engineer has specified F17 90 by 45 studs for a double height atrium. Do we use F17 for the top and bottom plates or just MGP10 which is what we're using for the rest of the build? The code doesn't seem to mention this requirement.

Woodsolutions Answer +

There is no problem combining different species of timber in wall frames as long as all members have the required structural properties, and all members conform to the same moisture profile, in this case 'seasoned' (15% moisture content or less). So you could combine MGP10 top and bottom plates with F17 seasoned hardwood studs, if MGP10 pine is suitable for the load situation. The adequacy of the MGP10 grade, and the size of plate required, will depend on whether the top and bottom plates are supporting any roof load, whether the roof rafters coincide with the studs or are supported between stud spacings and so on. Your engineer will be able to confirm these points. 

Wall framing

Answered on 22-09-2020
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

My question is to do with fixing top plates on internal braced walls to bottom cords of a truss,where there has been an allowance made for ceiling battens - as there is a gap between the top plate of the bottom cord of the truss of +/- 40mm.
My question is for braced walls parallel and walls right angles to, using wooden shear blocks:
1. What height block would you use on both blocked sides so as to engage the ceiling trimmers (noggins)? 35mm or even 45mm is maybe not enough...(?)
2. What size wall bracket to use, now it is significantly raised on top of a block? How much movement in the slots in a minimum?
3. How close are the blocks set to the noggins - are they butt joined or set off, if so how many mm's off from the ceiling trimmer?

Woodsolutions Answer +

AS 1684 requires a 10mm clearance between the top plate and the underside of the bottom chords of trusses, "or ceiling battens when used" (clause 6.2.5.2). Ceiling batten sizes given in Table 7.1 can be up to 35mm in height so 45mm shear blocks would only just reach the underside of the bottom chords and/or trimmers and clearly would be ineffective. AS 1684 doesn't provide an answer to your question 1 about the height of the blocks in this situation. Fig. (d) of Table 8.22 with ceiling battens doesn't show shear blocks, and Fig. (e) with shear blocks doesn't show ceiling battens. There is no guidance on situations with both ceiling battens and shear blocks. However, in our view the shear blocks would need to engage the full height of the trimmer. Regarding question 2, maximum movement allowed for needs to be the same as the clearance (10mm). Regarding question 3, the blocks need to be set close to the trimmers but not so tightly fitted as to restrain vertical movement. All major truss companies have engineers on staff who might be able to provide more detailed recommendations for your situation assuming, of course, that the higher shear capacity achieved with shear blocks is required for the building in question. 

Truss connections

Answered on 22-09-2020
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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