The cost for roof replacement can be less when you have an overlay. With an overlay, new shingles are installed on top of existing ones. So you'll save on labor costs and disposal. That might be a good idea if the layers underneath are in good condition, including metalwork, flashing, and decking (sheathing).

If any are worn, curled, slipped or missing tiles, it's a sign your roof may need replacing. At the very least you should look to repair broken and missing tiles as soon as possible. Also, check the ridge of your roof. This should be completely straight.

So how often should you replace your roof in California? The answer depends on a few factors, such as the type of roofing material, the climate, and how well the roof has been maintained. In general, however, most roofs will need to be replaced every 20-30 years.