How come houses are waterproof then Chid?
A good scratch coat and top coat of render with added waterproofer and then painted with exterior masonry paint will keep the water out..
because theres an outer skin of bricks and a layer of insulation............
That helps, but if a job's done properly, the only water in a cavity should be condensation from the inside and it should exit at the bottom via the weep vents. If the outside wall isn't waterproof, the water will bridge across the wall ties and cause damp on the interior walls. The insulation is there to stop heat loss, it isn