Before You Begin
Protect shrubbery and plants from falling shingles with drop cloths. Leave them covered until they're out of danger.
The project involves reroofing over an existing roof on a one-story house. It's assumed that there's only one layer of shingles on the house and they are worn, but basically sound. Before installing shingles, check to see if the flashing needs to be replaced. If so, use the old flashing as a template.
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Step 1 : Begin the starter course
When reroofing, the starter course is cut to just cover the exposed section of the first shingle. This course will level the step between the first and second course of old shingles. Begin this course so the tab slots of the shingle are offset from the shingles on the roof. Cut each shingle into lengthwise strips so they fit between the edge of the roof and the second course of shingles. Use roofing nails to fasten.
Step 2 : Begin the second course
The next course of shingles butt against the bottom of the existing third course. This places the shingle in alignment with the edge of the roof and provides a flat surface to place the next course on. You may have to trim the shingle to match the existing overhang. Don't line up the vertical seams of the old and new shingles, overlap them.
Step 3 : Continue working up the roof
Install the remaining shingles as you would on a new roofing project, but butts each new course against the bottom of the old courses. As you work, replace any old or damaged flashing around vent pipes or chimneys. You may have to add a spacer shingle beneath the flashing to raise the flashing to the new level of shingles.
Step 4 : Apply roofing cement
Use the caulk gun to seal the seams around the flashing with roofing cement.
Step 5 : Apply the hip and ridge caps
At the top of the roof remove the old hip and ridge caps before installing the last course of shingles. Use new shingles to replace the hip and ridge caps when all the other shingles have been installed.