We do not believe in installing shingles over existing shingles. Here are a few reasons why it is always better to remove your existing shingles: New shingles may not lay as flat over existing shingles – this results in your roof looking “bumped” up in certain areas. Plywood underneath the existing shingles cannot be inspected for damages that need replaced. On most roofs we install, it is usually necessary to replace even a minor amount of plywood. New technology cannot be installed under your new shingles. Excessive weight on your roof structure. Shingles are a tremendously heavy product and installing a second layer of shingles on your roof can produce a lot of stress onto the rafter system and plywood decking. This extra weight can cause “sagging” in your roof’s appearance. YOUR NEW ROOF MAY NOT LAST AS LONG. Shingles are an oil based product. The flexibility of the asphalt comes from the natural solvents within it. If you install a second layer of shingles over a “dried” out layer of shingles, this can cause the new shingles to “dry-out” prematurely resulting in your roof breaking down sooner than it should. Install flashings and other critical components of the roof system is much more difficult when a contractor cannot work with the wooden decking underneath. Many shingles today have “dark streaks” on them which is algae growth. Installing new shingles over this growth will provide a habitat for continued growth of the algae which results in a breakdown of your new shingles from the underneath side.