The ground point for the height measurement is in most cases the lowest ground surface around the walls of a structure. The point on the roof of the building where height is measured depends on the roof style and any roof dormers.
Where is height measured from?
To find out where to start the height measurement, you have to know the elevation of the ground surface located exactly five feet from all of the building walls. Is the ground surface completely level around all the walls, or does the grade of the surface slope?
Measuring the ground surface
Find the highest ground surface exactly five feet from the building walls and the lowest ground surface exactly five feet from the building walls. If there is a walkway no more than five feet wide that leads from the sidewalk to the entrance of the building, that is excluded from being a low point. If the property line is less than five feet from the building at any point, then the ground surface along the property line is used instead of the ground surface five feet away.
Finding the base point for measuring height (base reference point)
The base point for measuring height changes depending on whether the difference between the highest ground surface and the lowest ground surface is more or less than 10 feet. After finding the high and the low ground surfaces exactly five feet from the building walls, determine the difference between the two numbers:
- 10-foot or less difference: height is measured from the lowest ground surface
- More than 10-foot difference: height is measured from 10 feet above the lowest surface
Note, single-dwelling zone regulations include an alternative height measurement for lots that slope steeply down from the street, see Section 33.110.215.D.
Where is height measured to?
Building roofs come in different shapes and have different peaks and pitches, so multiple points on the roof are subject to the height measurement – they are called roof-type reference points. Height is measured from the base point to the highest roof-type reference point.
Flat roofs (pitch is 2 feet or less in height for each 12 feet in length) are measured to the highest point of the roof. If there is a parapet on the roof, the measurement is to the top of the parapet.
Mansard-style roofs are measured to the deck line.
Gabled, hipped, gambrel, or pyramidal roof (pitched roofs)
Pitched roofs are measured to the average height of the gable.
Other roof types
Domed, shed, or vaulted roof shapes are measured to the highest point of the roof.
Stepped or terraced building roof
Height is measured to the highest point of any segment of the building.
Roof dormers may also be considered a roof-type reference point for measuring height depending on how they are constructed. The height of a dormer is generally the point where it meets the main roof, because the dormer roof is usually a shed-type roof when considered on its own. If the dormer roof itself is a gable-style roof, it is measured to the average height of that gable.
Dormers are not included as a roof-type reference point and not included in the height measurement when they meet the following:
- The roof of the dormer has a pitch of at least 3 in 12 and no part of the dormer extends above the ridgeline of the main roof,
- The walls of the dormer are set back at least 12 inches from the plane of any exterior wall of the floor below, and
- The width of the dormer is not more than 75 percent of the width of the roof from which it projects.