I've a detached single brick thick garage. 2 sides of it form the boundaries with 2 neighbours.
It has a concrete slab, 2 courses of engineering (I understand to be water proof) bricks a DPC.
Now comes the problem. Both the neighbours gardens are approx 1 to 2 ft above my DPC. I figured out based on the height of the foundations of nearby buildings (the neighbours ' garages) that's how it was built, otherwise there'd be a huge angle to the ground between them.
Long story short can't do anything externally. The house was just inside the NHBC insurance/warranty and they wouldn't do anything because a garage is allowed to be damp. Something about classification.
So I've tanked the inside myself. I applied 2 coats of tanking slurry to the clean bricks within 24 hours of each other for a good bond. Now it's all dried (set) I still get water beading on it. I understand that to be condensation from the temperature difference between the air inside and the ground outside.
So it seems I now need to insulate internally.
How's best to do this? Timber frame and PIR between, ply/osb/plasterboard over the top of that?
I learnt early on that cast iron doesn't like cold garages in winter, so I've plasterboard and insulated the ceiling already (the door also has two sheets of PIR over it)