I have a lean-to approx. 20ft x 9ft. across the entire width of my house. it is single wall construction. I recently had new pvc windows doors and polycarbonate roof fitted. one side wall is adjoining my neighbours wall. the other side is brick and plasterboard and unobstructed on the outside. this wall has wet patches at approx. 4ft off ground level. they run along the join in plasterboard mainly, but are spreading across the entire wall. the paint is beginning to blister. could anyone advise me of what is responsible for this and how to treat it please? thanks.
