You have two alternatives:
- You can install another layer of asphalt shingles on top of the current layer of asphalt shingles.
- You can remove the current layer of asphalt shingles and replace them.
Which method you choose is based on a number of parameters.
The ability to install another layer of shingles on top of the current ones is based on numerous parameters. If any of the following items or conditions exist than you should remove the current shingles and install a new roof:
- There is already more than one layer of shingles on the roof.
- Some of the existing shingles have been replaced with shingles that are different than the originals.
- The current shingles are in very bad condition.
- Some or all of the roof decking needs replacement.
- Flashing needs replacement.
- The current roof ventilation methodology is not adequate.
- You want a new roofing material that is not shingles, e.g. tile, wood, metal, or slate
Note: Most roofing contractors will not replace existing flashing when re-roofing. The reason being that most flashing sits on the roof deck, below the existing shingles.
Although re-roofing is less expensive (primarily due to the labor cost of removing and disposing of the old roof) than installing a new roof, most manufacturers agree that the life of the roof will be reduced by as much as 25% if placed over old shingles. As well, any damage to the decking material or roofing felt, that may not be visible, will not be corrected.