I know this is an old subject but I feel strongly about the right way and wrong way to plasterboard a Velux (or any other brand of ) roof window reveal. So here goes. The reveal has 4 flat pieces of plasterboard: left, right and top and bottom. With me so far ? I don't need a diagram. Left, right and bottom must be vertical (parallel to the walls of the room), top must be horizontal (parallel to the floor ). It's that simple. The tendancy is to make top and bottom pieces at right angles to the ceiling.This is wrong in my view, it gives a tunnel-like aspect to the light entering the room whereas what is needed is to flood the room with llight. Mind you to achieve this horizontal top piece one has to plan carefully where to place the upper rafter spreader. (rafter catcher ? ) It means leaving a larger than reccomended gap between the top of the Velux frame and the spreader. In the current project I have a roof pitch of 30 degrees, a rafter depth of 7 inches, and the gap needed to achieve the horizontal top piece is around 12 inches (the recommended gap is 20-30 mm all round). To placate the tut-tutters I put an additional batten at the recommended gap but this one has a depth of only 45mm (in the current job) and must not encroach below the
finished plaster line.This means the thickness of plasterboard + skim has to be included in the plan. You need to do a sectional sketch to scale to get it right. Alright? Sorry for the mixed units! (Actually I'm not!). I see there is an option to include picture or sketch in this forum. I may include one if there is interest.