Your home's roof is under constant assault by the elements and eventually will need repair or replacement. One sign that your roof is in need of repair is when water is ponding on it -- sitting on the roof instead of draining away. Ponding often is caused by the roof buckling or sagging. Fixing this problem involves removing the old shingles, repairing the sheathing underneath and laying new shingles.
Position your ladder safely and climb up to the roof. Pry off the old shingles in the damaged area by sliding a pitchfork under them and lifting up. Take the removed shingles off the roof.
Inspect the plywood sheathing for signs of damage where you removed the shingles. Ponding often is caused by some of these sheets sagging. Remove damaged sheathing by pulling out the nails with your hammer. Take the sheets down from the roof.
Measure the area where you removed the plywood. Cut new plywood sheathing to this size with a circular saw, if necessary. Nail any loose plywood into the rafters with a nail gun. Nail the pieces of sheathing in place with the nail gun.
Cover the sheathing with pieces of 30-pound roofing felt. Cut the pieces to size with a utility knife. Lay the pieces of felt flat against the sheathing and overlap their edges by about an inch. Attach the felt to the sheathing with a hammer stapler, spacing the staples every six to eight inches.
Place the flashing along the bottom edge of the roof and around the chimney. Cut it to size with tin snips. Nail it into position.
Count how many shingles you need for the bottom edge of the roof. Cut off the tab portion of the shingles.
Lay the starter row of shingles along the edge of the roof, making sure they hang about 1/4 inch over the roof edge. Nail them into place with three nails -- one in the centre and one four inches in from each side.
Place the first row of full shingles into position over the starter row so that they hang about 1/4 inch over the roof edge. Drive four nails, evenly spaced, into the shingles about an inch above the tabs.
Start the second row of full shingles by aligning their bottom edges with the middle of the shingles in the first row, where the tabs begin. Stagger the shingles in the second row so their seams don't line up with those in the first row.
Drive two nails into each shingle, about an inch above the tabs and four inches from each side. Continue installing rows of shingles in this manner until you reach the peak of the roof, or your repair area is complete.
Install the ridge caps along the peak of the roof. Cut the tabs off of the shingles, then centre them over the peak. Drive in one nail in each side of the peak.
Exercise caution and use proper safety equipment when working on a roof. Set up your ladder in a safe manner, according to the manufacturer's recommendations.