Building height and number of stories: grade plane (Tables 504.3/504.4)

One-line orientation

Occupancy, construction type, and sprinklers set a building’s allowable height and number of stories. Both are measured from the grade plane. On a sloped site, identify the correct measurement point. Taller buildings generally need more fire-resistive construction.

Key points

• Two separate limits, two tables:
  • Table 504.3 — allowable building height in feet.
  • Table 504.4 — allowable number of stories.
  • The design must satisfy both at once.
• Three inputs drive both lookups: occupancy group, construction type, and whether the building is sprinklered.
• How height is measured: from the grade plane to the average height of the roof surface (the mid-height of a sloped or pitched roof, not the ridge).
• Grade plane on a sloped site: use the average finished ground level adjoining all exterior walls. It is not simply the midpoint between one high point and one low point.
• Tall buildings force a high construction type:
  • A very tall residential tower — say 310 ft — can only be built as Type I-A, which carries unlimited height.
  • For R-2 (apartments), Type I-B tops out at 180 ft / 12 stories (sprinklered, Tables 504.3/504.4) — anything taller is Type I-A only.

Confusions / comparison

	Table 504.3	Table 504.4
Limits	Height in feet	Number of stories
Same inputs	Occupancy + construction type + sprinklers	Occupancy + construction type + sprinklers
Must satisfy	Yes	Yes — both, independently

	Height measurement	Grade plane on a slope
Top reference	Average roof height (mid-height of slope)	—
Bottom reference	Grade plane	Average finished ground level adjoining the exterior walls
Common error	Measuring to the ridge	Using lowest (or highest) grade alone

Related

→ Allowable area: occupancy × construction type × sprinklers (this module): the area side of the same Chapter 5 analysis · Area increases: frontage and sprinkler (this module): sprinklers also raise height/story limits · Construction types (this module): why Type I-A buys unlimited height.