Log cabin/shed/summerhouse

[Thomo39]

Morning.
I'm just after some advice please on the following job.
I'm looking to build a glorified shed to house my hot tub in.
I have created the deck which is raised off the floor slightly and I plan to use some 25mm polystyrene floor insulation to help keep the cold out from rising through the decking.
The issue I have is that 2 sides of the summerhouse are going to be attached to the existing house, 1 side will be attached to an external garage which is constructed with single brick and the other side will be connected to the back of the house( recent extension) constructed by 100mm block, 50mm solid Kingspan then the single red house brick, so the question I have is can I attach kingspan or polystyrene insulation directly to these wall or would it be best to frame the wall and bring the insulation forward from the brick to create a ventilation gap.
I've attached a pic of the side of the garage and a pic of the back of the house
Thanks

 

[motorbiking]

You don't need to insulate any of the walls that are currently external walls as you are making them internal. btw 25mm of polystyrene is a waste of time. You need at least 50mm. Also make sure your hot tub room is well ventilated to prevent damp and there is a cover over the tub when not in use.