Under or over the roof structure? What do you prefer?
• Either between the rafters
Here the insulation is laid on the inside. You can choose to lay it in the traditional manner: between the rafters, or under the rafters, or even to combine both systems. But if you do, care should be taken: if the insulation is laid incorrectly, the greater number of joints can create thermal bridging, with potential humidity damage such as mould and fungus growth.
• Or over the rafters
Benefits: laying the insulation over a large flat surface area requires less work than between the rafters. But that is not the only reason. With this solution space is gained on the inside and there are many possibilities for future design plans. And because in this case, the whole roof structure is behind the layer of insulation, thermal bridging and rafter bending for example are simply impossible.