Installing a new roof on top of the old one isn’t recommended. You may save money in the short run on the cost of removing the old roof, but it will also cost you more in the long run. Not only will the life expectancy of your new roof be significantly reduced, but you’ll also spend more on energy costs. As a matter of fact, the life expectancy of your roof can be reduced by one-half, and in most cases, your warranties.
Here’s why. The second roof layer causes your roof to lose airflow, which causes the shingles to overheat. This speeds up the rate at which the ceramic chips flake off and the shingles dry out. This also causes your home to retain more heat, causing your air conditioning system to work harder.