If your pool has outlived its usefulness and it would cost more to repair than you can afford, you can cover it. Building a deck over a pool presents a challenge similar to any raised deck, so be prepared for hard work, sore muscles and a great sense of accomplishment. In addition to adding usable features to your yard, covering the empty pool removes a dangerous liability, turning it into an asset.
Assess the pool for safety. Check the bottom and walls of the pool for any signs of weakness that could lead to collapse. Make sure the pump system can be used as a sump pump to get rid of water and avoid mosquitoes. Make any necessary alterations to the pump system before building your deck.
Determine the dimensions of your deck. It will be easiest to run joists across the shorter distance of the pool rather than end to end. Make sure to measure well past the edge onto the concrete patio surrounding the pool to avoid any risk of the edge crumbling. Cut one joist for every 16 inches of the pool's length. Lay them out spanning the pool. If using composite decking, consider placing joists at 12-inch centers to accommodate the added weight. The weight of the deck will make anchoring it unnecessary, so lay the frame directly on the concrete.
Lay a 2-by-8 on edge the length of the pool on the patio or pool deck. This will serve as the outside frame. You may not be able to get lumber to span the entire length in one piece, but the fewer the better. Wherever there is a joint, add a double joist across the pool. Using joist hanger brackets, attach the joists to your outside frame on 16-inch centers. Attach one side of the bracket, set your joist into the bracket and attach the other side. Use as many screws as the bracket will allow.
Add 2-by-8 legs in the center of the pool, from the bottom to even with the top of the joist, about every third joist. Attach a square 2-by-8 to the bottom of each leg to avoid damage to the pool bottom. Attach the legs to the joists with screws. These will help to distribute the weight more evenly and avoid sagging. For a wide pool, (more than 8 feet) or if you're using composite decking, consider two rows of legs spaced evenly from the center of the pool.
Place your decking, starting in one corner. Make sure to put at least two screws in each joist. If you are using composite material, you may want to use clips to avoid unsightly screw holes. Consult your manufacturer's catalog or website for more details on your specific brand. Work about four or five rows out and use them as a platform to work from, moving on to the completed decking as you go. Make sure to stagger the end joints between strips of decking to add strength. Consult the manufacturer's instructions for recommended spacing between rows (usually 1/8- to 1/4-inch) and follow their guidelines for best results. As much as possible, use full lengths and leave the overhang until decking is completed. Make sure that all board ends meet as close to the center of the joist as possible to provide strength.
Mark a straight edge with a chalk line at each end and cut off any overhanging boards with a circular saw. Cutting them in one action will give the straightest line, save the time you would have spent fussing with matching them up and make the best use of material. Add rails, benches or planters built from decking cutoffs for a finishing touch.