HI, I AM DRYLINING A FIRST FLOOR BEDROOM(OUTSIDE) WALL AND I HAVE A NUMBER OF QUESTIONS. THE FIRST IS WHAT IS THE IDEAL GAP BETWEEN THE MASONRY AND THE INSIDE OF THE PLASTERBOARD, ESPECIALLY AS I WANT THE SPACE VENTED. THIS LEADS ON TO MY NEXT QUESTION, WHAT IS THE BEST WAY TO VENT IT. MY NATURAL IN...