WoodSolutions doesn't engage in R & D projects, but our 'parent' organisation, Forest & Wood Products Australia (FWPA), is one of the bodies that supports Australia's National Centre for Timber Durability and Design Life. You can log onto the Durability Centre's website via this link https://research.usc.edu.au/esploro/research-units/61USC_INST___24?institution=61USC_INST. 

You might be thinking of a 4-part webinar that was promoted by WoodSolutions but actually hosted by Timber Queensland in 2022. A fee applied to take part. We understand it is no longer available, although you could check with Timber Queensland in case they have other resources. We have a 3-part webinar that is still accessible and free of charge.

If the blackbutt screen is required by regulations to prevent embers from accumulating under the floor, the screen would have to be a lapped cladding profile with sub-floor ventilation openings protected with mesh. Fixings would be to suit the cladding profile. Alternatively, 70 x 30mm timbers could be spaced apart with mesh protecting the gaps. The mesh must be corrosion-resistant and have a maximum aperture of 2mm. These requirements only apply if the house floor is less than 400mm above finished ground level. If the screen is not required to prevent embers, ie.

Australian Standard 1684 Part 2, Residential timber-framed construction, contains the following requirement: Boards over 85mm cover width shall be fixed with a minimum of two face nails at each joist....nails shall be skewed slightly to the vertical in opposing directions....the mechanical fixing shall be supplemented by a minimum 6mm bead of polyurethane or polymer flooring adhesive to the top surface of the joist (Clause 5.5.2.2).

From your photo it looks as if the cladding has shrunk and split off part of the lap. Glue won't stop timber from moving in response to moisture changes. It just allows stress to build up in the timber until it's relieved by a split or by the joint opening up. So the short answer is that the timber has to be allowed to move. As long as the timber isn't restrained, a lapped joint permits movement without detracting from overall appearance, unlike other joints where gaps caused by movement are more obvious. We assume the cladding isn't fixed to the steel.