To make and trim an opening in a floor you require some stout pieces of timber to use as props on the underside of the floor.
1 When you have worked out the position of the hole, your first job is to support the floor. The props can stand on a sole piece, resting on the top of the floor below: otherwise the props will have to be taken down to a solid base.
2 Once the floor has been supported, the floorboards can be cut and removed. A power circular saw, set just greater than the depth of the floorboards, can be used.
3 Next, cut the ceiling. Score the underside of the ceiling with a handyman’s knife to the shape of the opening and then cut away the unwanted plasterboard.
4 Cut the joists so that a butt housing joint can be formed on the end of the joist. Cut housings into the trimming member. Similarly, joints can be formed in the ends of the trimming member. The only difference is that the housing would be twice as wide as the width of the timber so that the trimming member can be dropped into position and then pushed on to the ends of the joists.