What is the minimum extension required for concrete or masonry under appliances above the adjoining grade?

The minimum extension for concrete or masonry under appliances above the adjoining grade being four inches is aligned with the intent of providing proper drainage and preventing water from pooling around the appliance. This extension acts as a barrier, diverting water away from the foundation or base of the appliance, which helps protect it from water damage and contributes to the overall stability and longevity of the installation.

Setting this minimum extension ensures that there is enough distance to address surface water runoff effectively. Options that propose either a smaller or larger extension might not adequately address the necessary protection, or could be excessively conservative beyond what the code intends, making four inches the standard that balances functionality and safety.