Firstly the insulation manufacturers guidance must be considered. They will have a recommended fixing pattern which must be achieved as a minimum. 

The type of fixing used can be advised by a fixing manufacturer and must be suitable for the insulation in question and the substrate it is fixing through to. Siniat Weather Defence board will be fixed to a stud frame at max 600mm centres, which can be either timber or metal depending on the design of that element. The insulation fixings chosen will need to suit the studs and gypsum board where there are board only fixings and be able to resist the loads that they are subjected to. The pull out resistance an individual fixing can achieve will be down to the type and substrate.

The extract below is from the Siniat Weather Defence brochure which can be found on the Siniat website.