How to Build a New Roof Over an Old Roof

Save money by installing your own second roof.

Roofing contractors refer to the process of building a new asphalt roof over the top of an old one as re-roofing, which is a money-saving and efficient way of adding a new asphalt roof to a house. Local codes and ordinance will dictate the number of roofing layers, or re-roofs, allowed on a roof safely. Only install a new roof over an old one if the existing roof is structurally sound.

Things You'll Need

• Hammer
• Galvanized roofing nails
• Metal scraper
• Roofing tar
• Masonry paintbrush
• Metal drip edge
• Shingles
• Utility knife

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Instructions

1. Obtain required permits and follow all local codes and ordinances.

2. Examine the plywood sheeting from the attic to determine if the roof is structurally sound. If the plywood shows extensive water damage, rot, warping, twisting or separation, re-roofing is not an option. Complete roof replacement is necessary.

3. Inspect the roof thoroughly for popped nails and hammer them back in place. Nail in loose shingles with galvanized roofing nails.

4. Scrape away roofing tar from around vent stacks with a metal scraper. Apply new roofing tar with a masonry paintbrush.

5. Position a metal drip edge, which protects the plywood from water damage and rot, along the edge of the roof and nail in place with galvanized roofing nails.

6. Set the first shingle on the bottom edge of the roof, allow the shingle to hang over the edge of the roof by two inches; face the shingle tabs toward the roof peak. Drive a galvanized roofing nail through each shingle tab and into the plywood to secure in place. Place the second and following shingles, partly covering each other by two inches, along the row until reaching the opposite edge. Roofers call the first row the starter course.

7. Position a roofing shingle straight on top of the first shingle in the starter course with the shingle tab facing toward the bottom edge of the roof and hammer a nail through the shingle into the plywood to secure in place. Set the second and following roofing shingles in place, covering each other by two inches, over the top of the starter course.

8. Begin the second row at the edge of the roof. Position the tabs pointing up toward the peak with the shingle hanging off the edge six inches. Staggering seams by six inches is necessary for proper roof water shedding. Secure the shingle with a galvanized roofing nail and then cut off the six-inch overhang with a utility knife. Continue to cover the row.

9. Stagger each row, switching between starting at the roof's edge and starting with a six-inch overhang until arriving at the roof peak. Repeat on the other side of the roof.

10. Trim the tabs off a roofing shingle with a utility knife and set the shingle across the roof peak with like amounts of the roofing shingle on each side of the peak. Secure in place with galvanized roofing nails. Repeat until the shingles cover the roof peak.

Tips & Warnings

• Wear a safety harness, gloves and safety glasses when working on a roof.

• Use only safe and secure ladders or scaffolds.

References

• "Time Life Editors"; Roofs and Siding; 1979
• "Reader's Digest Complete Do-It-Yourself Manual"; Family Handyman Magazine Editors; 2005