Hi folks, building a conservatory with block work cavity walls and bifolds. I’m putting a roof lantern on that’s the size of the floor, so will sit on the inner leaf. There’ll be a slim flat roof/gutter on top of the cavity wall (I’ve made it a bit wider for looks, so it’s about 400mm wide). I’ve got OSB on that’s flat on the roof/gutter at the moment, and am putting another layer of OSB with the correct falls on over that, which I’ll GRP. Do I need to put insulation or anything else in the void between the layers of OSB? Doesn’t feel like there’s a need for the top of a wall to be insulated given it doesn’t cover any of the actual room, but I’m not sure if leaving empty space is asking for problems with condensation etc. any thoughts??? Mike