It has been suggested (see the other thread) that a traditional "lean to" might be a better option than a Garden Room (sigh). And I was ready to push the button.   What we are talking about is an unheated lean to on the side area of a house against a blank wall with, perhaps, a roof of corrugated polycarbonate or 2/3 layer polycarb as is used on some conservatories. It will be dry but unheated. If you think of a car port with the walls enclosed you get the idea. There will be a door to