Installing shingles over your current shingles can save you money, time and labor by not having to tear the old roof materials off. Some figures are approximately 25% savings over removing the old shingles.
If you live in a snowy climate, you might need to confirm that the added weight of the extra shingles will not cause roof damage. A very hot and humid climate may also not be conducive to the extra shingles as it may cause extra heat buildup.
Getting the Roof Ready
There is still preparation work to do before you can lay the new shingles. Check the roof decking for any signs of water or other damage and make any necessary roof repairs.
Replace any missing or loose shingles. Hammer down any protruding nails and clear off any debris from the roof. Some roofers suggest laying down new underlayment or felt in between the old and new shingles and adding new flashings.
Check building codes in your area to determine how many layers of shingles you can have on your roof. Most areas allow you to add 1 new layer of shingles over the old roof. The main reason for the concern is that it makes it difficult to inspect the roof deck and underlayment. Also make sure the materials warranty is covered if you put the new shingles on top of the old.
