While there could be some initial cost-saving in laying new shingles over an old, aged roof, we generally don't recommend re-roofing. Old shingles also mean an old roof deck. By tearing off the old shingles, our licensed roofing contractor will then be able to spot any areas of instability or damage to the roof deck that may have been hidden by the shingles. We can replace any sections where there may be wood rot. Roof installation techniques and materials have also changed over the last couple of decades, and your old roof may not be up to code. "Re-roof" jobs may also not carry the same warranties as a full replacement.