If you've got a high a solid floor and open joists underneath, and there's usable space down there that could be a sitting area, there's no reason you can't install a ceiling under the deck. Buy tongue-and-groove planks designed for porch ceilings, since that is essentially the same project. This should only be done when the deck above has a solid tongue-and-groove floor in place; if it's an open deck with spaces between the floorboards to allow drainage, you can't put a ceiling below it.
Instructions
1. Measure the underside of the deck, perpendicular to the direction of the deck joists, using a measuring tape. Transfer the measurements to a ceiling plank with a pencil. Use a miter saw to cut the plank to that length.
2. Hold the cut plank to the underside of the deck along one side, perpendicular to the joists, with the grooved side of the board facing the edge. Leave ½ inch between the board and the edge. Use a trim nailer to put two nails in the surface of the plank at each place where it crosses a joist.
3. Cut additional planks to size. Fit each one against the one before it, knocking them tightly together by their tongue-and-groove milling, using a rubber mallet. Nail the subsequent planks by shooting one nail through the outer side of the board, just above the tongue, at each point it crosses a joist. This will keep the nail heads hidden when the next course is hung.
4. Cover the entire space with interlocking boards. Length-cut the last board on a table saw so it fits against the end of the space with a ½-inch gap at the edge.
5. Measure and cut ceiling trim on your miter saw to fit around the perimeter of the underside of the deck. Install the trim with the nailer, letting it cover the ½-inch gaps at the ends.
Tags: underside deck, , deck with, side board, space with