How to Make a Wood-Framed Roof Watertight

Install drip-edge flashing along the bottom edge of the roof. This is a metal strip that covers the bottom edge of the roof and prevents water from seeping up underneath the shingles. Use galvanized nails when installing flashing.

Install an ice and water shield (sometimes called a waterproof membrane) along the bottom edges of the roof and the roof valleys. The shield has an extremely sticky adhesive on one side, and is installed by unrolling it onto the roof and pressing it flat against the roof. The shield protects the roof against leaks caused when water trapped by ice dams pools on the roof. Ice dams occur when melting snow freezes, creating a dam that prevents water from flowing off the roof when the snow begins to melt again.

Cover the plywood or oriented-strand board sheathing of the roof with roofing felt. This is a heavy, asphalt-saturated paper that prevents water from reaching the sheathing. Begin laying the paper along the base of the roof; work toward the peak, overlapping the edges of adjoining strips by an inch. Lay the paper flat against the sheathing, and staple it to the roof every 6 inches.

Nail flashing to the roof along any valleys in your roof. The valley is where two different sections of roof meet at an angle. Start at the bottom of the roof and move up toward the ridge. Overlap the edges of the flashing by an inch, with the top edge of the flashing covered by the next piece.

Nail flashing along the edges of the chimney where it comes into contact with the roof. Begin the installation at the lowest point around the chimney, and overlap the edges of the flashing.

Install flashing or a rubber gasket around any roof vents that do not have flashing pre-installed around the edges. Attach the flashing to the roof with nails; if you're using a rubber gasket, place a thick bead of roofing cement between the roofing felt and the gasket.

Install the shingles on the roof, nailing them down with roofing nails. Start along the bottom edge of the roof, and work toward the ridge. Cover the top half of the shingles when laying the next row, and stagger the shingles in each row so that the joints between them are not aligned. When installing shingles around an object such as a chimney or roof vent, apply a thick bead of roofing cement to the bottom edge of the shingle to prevent water from leaking through.