A trapdoor in the floor provides you with a quick and convenient method of moving between floors, a closeable door in the floor of a loft, or a way to access a crawlspace beneath your floor. Making the trapdoor is just like creating any doorway in a wooden frame. You need to cut and reinforce an opening, and then create the door frame and door.
Strip away any floor covering material over the proposed trapdoor area. Use a prybar to remove floorboards and tile, or roll up carpeting to expose the subfloor beneath.
Mark the trapdoor location on the subfloor using a piece of chalk and a straightedge. Put a carpenter's square on the floor at each of the corners as you draw them to make certain that each corner is 90 degrees. There are no set sizes of trapdoors; the size you set is determined by the trapdoor used. Add 2 inches to the dimensions of each side of your trapdoor to allow for an overhang of the door over the hole's location.
Set a circular saw's depth to equal the depth of your subfloor's paneling. Cut through the subfloor along the chalk lines and then pull the paneling from the floor joists with a prybar. Mark the edges of the opening onto the floor joists with the chalk.
Examine the run of the floor joists that you exposed when you cut the hole in the subfloor panels. Remove all floor panels in the room covering those joists, as well as the nearest adjacent joists to both sides of the hole in the floor with the prybar and then set them aside for later use in covering the joists.
Reinforce the adjacent joists by cutting matching floor joists with the circular saw from lumber planks measuring the same size as the planks used for the joists. Place the matching joists against the side of the adjacent joists sitting away from the hole. Nail the new joists to the old using framing nails and a framing nailer. This will reinforce those joists to support the weight of the floor previously supported by the removal of the joists spanning the trapdoor hole.
Place a second mark on the floor joists located 3-inches outward from the marked edges of the hole. Cut the floor joists along the second markings with a reciprocating saw, and then pull the joists free. This leaves you with the doubled adjacent joists to either side of the hole and partial joists beneath the trapdoor location.
Measure the distance between the doubled joists. Cut four pieces of the floor-joist sized planks to match the distance. Set two of the planks between the adjacent joists on either end of the hole so that the planks are flush with the top and bottom of the joists, and cover the ends of the partial joists. Nail the doubled planks in place, driving nails through the planks and into the ends of the partial joists, as well as through the planks and into the adjacent double joists.
Measure the space between the doubled planks that you set between the reinforced joists. Cut two floor joist-sized planks to match the measurement and then nail them in place between the doubled planks spaced so that they're flush with the proposed trapdoor opening.
Replace the subfloor panels, nailing them back into the floor joists. You should have a framed trapdoor hole beneath the opening with the double planks overlapping the hole by an inch on both ends of the opening.
Drill a hole through the four corners of the framed floor of the trapdoor hole, which should be the ceiling of the floor below the trapdoor. This will mark the perimeter of the trapdoor on the ceiling for easy cutting.
Go to the floor below and join the four holes drilled through the ceiling into a square by snapping a chalk line around the perimeter. Cut through the ceiling using a keyhole saw along the chalked line, and then remove the ceiling panel.
Trim the outside edge of the trapdoor hole in the ceiling with wooden door trim, nailing the trim in place with finish nails and a hammer.
Return to the floor above. Cut a trapdoor cover for the hole sized to match the hole's dimensions from a 3/4-inch plywood sheet of your desired wood choice. Place hinges onto the side of the frame, and on the edge of the door using wood screws. Measure the depth of your recessed cabinet pull handle, a latched circle within a circle that sits recessed in the door. Drill a hole into the door the same diameter as the handle to the measured depth of the handle, and then use construction cement on the outer handle edge to set the handle in place. Allow the glue to set overnight before using the door.