A gable is the part of the side wall of a building above a line between the eaves. It can be looked upon as the part of the wall that seals the end of the roof structure. When a gable consists of a sloping roof rather than a flat one, the gable forms a triangle. A gable end is the gable and the wall beneath it. Calculating the area of a gable end, where the roof slopes, involves calculating the area of a triangle and of a rectangle.
Measure the width of the wall below the gable. This is typically the width of the building. Record the distance.
Measure the height of the wall from ground level to the top of the eaves, the point where the lowest part of the roof meets the top of the side walls. Finally, measure the height from the ground to the top of the roof ridge, the highest point on the gable.
Calculate the area of the wall below the gable by multiplying the width of the wall by the height of the eaves. For example, if the wall is 25 feet wide and the eaves are 20 feet above ground level, the wall has a surface area of 500 square feet: 25 x 20 = 500.
Deduct the distance from the ground to the eaves from the distance from the ground to the roof ridge. The result is the height of the gable triangle. For example, if the building is 30 feet high and the eaves are 20 feet above ground level, the gable height is 10 feet: 30 - 20 = 10.
Calculate the area of the gable using the formula: gable area = width x (height / 2). Using the example width of 25 feet and gable height of 10 feet, the surface area of the gable is 125 square feet: 25 x (10/2) = 125.
Combine the area of the wall and the area of the gable to determine the area of the gable end. To conclude the example, the gable end has an area of 625 square feet: 500 + 125 = 625.