What is the minimum number of layers of No. 15 asphalt felt required for exterior wall veneer?

For exterior wall veneer, the minimum requirement is one layer of No. 15 asphalt felt. This layer acts as a water-resistant barrier, helping to protect the underlying structural components from moisture damage.

When building codes specify a single layer, it indicates that this amount is sufficient to provide the necessary defense against rain penetration while allowing any moisture that does breach the veneer to escape.

Additional layers, such as two or more, may provide enhanced protection or meet specific design elements, but they are not the minimum standard. This is crucial for ensuring the wall assembly remains functional and safe while still adhering to construction efficiency and cost-effectiveness.

The other options, which suggest two, three, or four layers, exceed what is required for a standard installation, making them unnecessary in this context. The focus is on achieving adequate moisture control while maintaining the integrity and performance of the wall assembly.