New asphalt shingles go over the old

Q. I plan to reroof my 19-year-old house. Should I apply new asphalt shingles right over the old ones? The south-facing shingles are in poorer shape than those on the north. Are there any disadvantages to reshingling in June or July? Christopher E. Hawk Canton, Ohio

A. Your 19-year-old composition roof-shingle job has performed well. The roof pitch apparently is steep enough to contribute to the longevity as are the quality and weight of the original shingles. The better the material the greater the longevity.

If the existing shingles are only one course deep, apply the new composition shingles atop the old. The new roof should thus last longer than the old one.

Since there are various grades or weights of asphalt shingles, review the available choices and prices. Select the shingle that will last the longest against the cost.

Reshingling may be done any time the wea ther is dry.