A roof measuring 40 feet by 20 feet with a vertical wall on one side measuring 4 feet by 40 feet, _________________________ must be added to the roof area to determine minimum roof drain square feet?

To determine the minimum roof drain square footage, it is important to consider both the horizontal area of the roof and any vertical wall surfaces that contribute to water drainage. The roof measures 40 feet by 20 feet, which gives a total horizontal area of 800 square feet (40 x 20).

In addition to this, you have a vertical wall measuring 4 feet by 40 feet. The wall represents an area of 160 square feet (4 x 40). This vertical wall area is crucial because it typically collects rainwater and adds to the total amount of water that the drainage system must handle.

When you add the areas together, the minimum roof drain calculation must include both the roof area and the vertical wall area, resulting in 960 square feet (800 from the roof plus 160 from the wall).

In the context of the question, therefore, it is essential to factor in the vertical wall area when determining the required drainage capacity of the roof system. The answer of 80 square feet reflects the additional area attributed to the vertical wall, supporting the calculation of 960 square feet as the effective drainage area.