How to build cabana roof with exposed rafters?

[MattyE1]

Building a small 19m2 pool cabana with exposed rafters. 6 degree pitch skillion colorbond roof. 

I've come from Europe where a typical roof construction for this would be OSB screwed to the top of the rafters, a waterproof bitumen-based self adhesive roll product, 45x90 roof battens, metal roof sheets. (Only used in the North European summer so no insulation used). I get that the OSB is not needed for the roof construction - can just do metal on battens -  but that wouldn't be pretty on the underside with exposed rafters. I can't really find much detail on this technique in Australia. I want to make sure i don't have condensation issues and I'd also like to include an insulation layer as it gets hot here in the summer. So i was thinking OBS, waterproof/membrane roll product, battens, Bradford Anticon 60mm (Installed vertical over battens as described in their preferred installation method), Colorbond. What membrane product do i use between the OBS and the Anticon. Or is there a better/alternative all-in-one product that will act as both the membrane and insulation? I'd prefer a combined foil reflect and batt product that the Anticon offers but could just go with a permeable membrane and foil product if it exists. 

[MitchellMc]

Welcome to the Bunnings Workshop community @MattyE1. It's wonderful to have you join us, and many thanks for your question about roofing construction.

In Australia, we generally use a simpler approach. For a small structure like a cabana, Colorbond sheeting is typically fixed directly to the rafters or to purlins/battens running across them, keeping the construction straightforward and cost-effective. If you’d like to include insulation, Bradford Anticon is an excellent option as it’s designed specifically for use under metal roofing and comes with a foil (sarking) layer bonded to the insulation. This foil acts as a water-resistant barrier, eliminating the need for an additional membrane over your rafters. The Anticon helps manage condensation effectively while also keeping the space cooler in summer. 

For a more polished appearance on the underside, you could line it with decorative sheeting such as plasterboard (if the area is enclosed and protected), fibre cement sheeting, or even timber lining boards for a natural look. A typical setup would involve installing rafters, adding battens, laying Bradford Anticon over them with the foil facing down, and then fixing the Colorbond roofing on top. This method gives you insulation, condensation control, and a neat, low-maintenance roof system without the need for OSB or multiple membrane layers.

Please let me know if you have any questions.

Mitchell
 

[MattyE1]

Thanks for the quick reply. I might just have to simplify things!