Building Height Determination

Question

How do I determine if a building is a high rise?

Discussion

According to Massachusetts General Laws (MGL), all high rise buildings (with a few exceptions) are required to be fully equipped with a sprinkler system. Chapter 148 §26A, enacted in 1973, covers all high rise buildings constructed on or after January 1, 1975. Chapter 148 §26A½, enacted in 1986, covers high rise buildings constructed before January 1, 1975. The Massachusetts Fire Safety Commission, created by MGL c. 6 § 200, developed 530 CMR 2.00, Installation of Automatic Sprinklers in High Rise Buildings and Structures. 530 CMR was enacted in 1993, and is only applicable for MGL c. 148 §26A½.

Generally, what makes a building a high rise is a height greater than 70'. For buildings close to the 70' threshold, the measurement of height is a critical factor in determining whether or not a building is in fact a high rise.

High Rise Buildings Built before January 1, 1975
Within 530 CMR there are two ways to determine the building height, depending on street frontage. 530 CMR 2.02 defines building height as follows:

Height, Building The vertical distance from the grade to the top of the highest roof beams of a flat roof, or to the mean level of the highest gable or slope of a hipped roof. When a building faces on more than one street, the height shall be measured from the average of the grades at the center of each street front.

Grade A reference plane representing the average of finished ground level adjoining the building at all exterior walls.

For buildings with frontage on one street only, height is measured using the first sentence of "Height, Building." The reference plane is established using all exterior walls of the building, including the street wall.

For buildings with frontage on two or more streets, the height is measured using the entire definition of "Height, Building." What differs is how to establish the reference plane. The reference plane is established using only those exterior walls with street frontage; all other exterior walls are not used.

In both cases, the actual building height is the distance between the reference plane and the top of the highest roof beams.

High Rise Buildings Built after January 1, 1975

Chapter 148 §26A does not have any dedicated definitions for determining building height, so the default definitions have been those of 780 CMR, the Massachusetts State Building Code (the "Code"). As the Code has changed, so also have these definitions. Following are all applicable definitions since the enactment of c. 148 §26A.

First through Fourth Editions of 780 CMR (1975-1992):

Height, Building The vertical distance from the grade to the top of the highest roof beams of a flat roof, or to the mean level of the highest gable or slope of a hipped roof. When a building faces on more than one street, the height shall be measured from the average of the grades at the center of each street front.

Grade A reference plane representing the average of finished ground level adjoining the building at all exterior walls.

These definitions are the same as those in 530 CMR.

Fifth Edition (1992-1997):

Height, Building The vertical distance from the grade to the top of the highest roof beams of a flat roof, or to the mean level of the highest gable or slope of a hipped roof.

Grade A reference plane representing the average of finished ground level adjoining the building at all exterior walls. When the finished ground level slopes away from the exterior walls, the reference plane shall be established by the lowest points within the area between the building and the lot line or; when the lot line is more than 6 feet from the building, between the building and a point 6 feet from the building.

Note that the second sentence of "Height, Building" has been removed, so street frontages have no impact on determining building height. The definition of "Grade" has been changed from "average" ground levels to "lowest" ground levels. The location of the "ground level" has been moved from the exterior wall to the lot line or a point 6' from the exterior wall, whichever is less.

Sixth Edition (1997-present):

Height, Building The vertical distance from the grade plane to the average height of the highest roof surface.

Grade Plane A reference plane representing the average of finished ground level adjoining the building at all exterior walls. When the finished ground level slopes away from the exterior walls, the reference plane shall be established by the lowest points within the area between the building and the lot line or; when the lot line is more than 6 feet from the building, between the building and a point 6 feet from the building.

The point of measurement of height on a building has changed from "to the top of the highest roof beams of a flat roof, or to the mean level of the highest gable or slope of a hipped roof" to "the average height of the highest roof surface." "Grade" has been changed to "Grade Plane," although the definition has not changed.

SUMMARY

All buildings greater than 70' in height and constructed prior to January 1, 1975 are subject to the definition of building height as in 530 CMR. These definitions have remained unchanged.

All buildings greater than 70' in height and constructed on or after January 1, 1975 are subject to the definition of building height as in 780 CMR. These definitions have changed. It is possible that a building constructed prior to the sixth edition of 780 CMR would not have been considered a high rise building, but could be considered a high rise building under the sixth edition definition.