I'm getting a large new shed built in my garden and I'd like to insulate it to make it a bit more comfortable to work in.
The shed comes with stud framework on the walls, so my plan is to use OSB to board the walls up and create a cavity, and fill those cavities with insulation, similarly to how this article recommends. I'll likely do the same for the sloped roof, but with plasterboard. I figure that OSB will be harder wearing than plasterboard for the walls, and I can paint it for a little aesthetic improvement. The shed only has tiny security windows so there's not a lot of extra work to accommodate those. I'll be installing a pair of roof vents for air blowers (one in, one out), to help circulate air for cooling and damp prevention.
I'm in England, so we're talking temperature extremes of -10°C to +35°C, but generally between 5°C and 25°C for most of the year. The humidity is all over the place but it's generally quite high around here.
My main concern is the heat rather than the cold. A little foam insulation and a small electric heater should do fine in the winter. But I struggle with heat as it is, so the last thing I'm going to want to do is sit in an oven while I work on some DIY job in the summer. I'm struggling to find solid information about options for maximising heat rejection in this context, and I'm concerned about picking a "stackup" of insulation that does the job but runs into damp and condensation problems.
What're my best options here? Which types of insulation (or configurations thereof) have better heat rejection properties? Does it make sense to go for something like a foil-backed panel on the external side and slab behind it? Do I need breather membranes or other damp control layers?