When replacing a roof, it is generally best to remove the existing shingles and replace the entire roof rather than adding more shingles on top of the existing layer. This is known as a complete roof replacement.
Here are a few reasons why replacing the entire roof is usually recommended:
Structural integrity: Adding multiple layers of shingles can significantly increase the weight on the roof structure. This additional weight can strain the structure and potentially lead to structural issues over time.
Proper installation: By removing the existing shingles, the roofing contractor can inspect the underlying structure for any damage or issues that may need repair. They can also ensure that the new shingles are installed correctly and in accordance with industry standards.
Longer lifespan: A completely new roof will generally have a longer lifespan compared to a roof with multiple layers of shingles. Starting with a clean surface allows for better installation, which can contribute to the longevity of the new roof.
Visual appearance: Adding new shingles on top of old ones can result in an uneven appearance due to variations in the thickness and texture of the different layers. Removing the old shingles and installing new ones provides a more uniform and aesthetically pleasing look.
It's important to note that local building codes and regulations may also play a role in determining whether multiple layers of shingles are allowed. In some areas, building codes may prohibit more than one layer of shingles for safety and structural reasons.
To make an informed decision about whether to add shingles on top of an existing roof or replace the entire roof, it's best to consult with a professional roofing contractor who can assess the condition of your current roof and provide you with the most appropriate recommendation for your specific situation.