If you have only one layer of asphalt shingles on your roof you may be able to re-roof over your existing one. Be aware that some shingles installed over an old roof won’t last as long. If there are no leaks and your old roof is in good condition with just one layer of shingles it can be cost effective to put a new layer of shingles over the existing ones and avoid a tear off.
While it is similar to a regular roof job, the starter shingles are different in that they will need to have the top edge trimmed off of the roofing material. Nail the starter shingles along the entire bottom edge of the roof. The starter shingles will be covered with full size shingles and butt successive courses against the bottom of the following courses. The rest of the shingles can be applied in the regular installation process.
Change out old flashing and ridge caps
Apply new flashing where missing or damaged. Old hip and ridge caps will need to be removed and repaired with new shingles. Make sure the nails are long enough to go both layers of shingles and into the roof deck by ¾ inch.
It is always better to tear off old shingles and install a new roof that way you can see any damage to the sheathing underneath. Most building codes allow 2 layers of shingles, any more than that and it becomes a weight issue. You can ask your local roofer what the codes in your area allow.
