Insulating a single skin garage

Hi,

I have a detached brick single skin garage (no dpm), on the whole it's pretty dry save some occasional 5mm damp marks where the brick meets the floor, where I have painted the inside the paint is mostly still there save occasional bits over the mortar (planning on treating the outside with water repellant stuff). I am looking to insulate it to use it as an occasional office and gym. It's a flat roof which is being redone now. My plan was:

1. Leave the main garage door in place, build a stud wall with 50mm kingspan behind it (wife concerned about removing the door for some reason).
2. Stud the rest out with 50mm studs and kingspan as well
3. Membrane round the whole thing
4. 12mm Ply round walls (to attach pallet wood)
5. Attaching recycled wooden pallet wood round the entire wall.
6. Floor kingspan, vapour barrier then laminate (uninsulated slab, always seems dry).
7. LED Lighting, 3 x 600 watt convection heaters

The membrane is because the wood will not likely be enough of a barrier for warm air to potentially get to cold brick.

Am I asking for trouble by cladding in wood? Is it a fire hazard / death trap?

Thanks

Graham

Single skin, no DPM, - your main problem will be damp.
At the moment it's able to evaporate, if you cover with insulation you'll need to make sure it being soaking wet behind won't cause a problem.
By way of comparison, with a house normally you'd have a drained cavity 50mm and a ventilated floor void 150mm to prevent problems with the timber.

And the work is notifiable BTW, just so you can make an informed choice.

Okdokay, had assumed I would have to tell someone! Does it need to pass planning permission though?

Given my description above, is there any way to do this without a drained cavity type scenario? Some people have suggested dpm straight against the wall and insulated plasterboard straight on top?

Thanks

Graham

Of course if you put a DPM around the wall and floor and make sure it's continuous ie laps and penetrations sealed then you'll be dry inside. You can try to avoid the condensation issue by making sure there are no voids and the rigid insulation is hard against the wall.
Your challenge there is how to attach the plasterboard to the DPM without making holes in it.
There's a good reason cavity walls have been settled on as the standard, it's because a drained cavity is 100% reliable against water penetration. Anything else is a risk so no one will tell you it's definitely fine.