Height Limit Calculations

Last updated March 27, 2025
By Ian Story

Method A – Smallest Rectangle

• Draw the smallest rectangle that encloses the structure.
• Measure the existing grade midpoint elevation of each side of the rectangle.
• Take the average of the midpoint elevations, weighted by side length.

Method B – Midpoints of Exterior Walls

• Draw a perimeter polygon that follows the exterior walls of the structure.
• Measure the existing grade midpoint elevation of each edge of the polygon.
• Take the average of the midpoint elevations, weighted by edge length.

Method C – Lowest Points in Vicinity of Building

• Draw a perimeter polygon that follows the exterior walls of the structure.
• Draw a larger polygon offset 6 feet from the primary polygon. Clip to fit within the lot lines where the structure is less than 6 feet from property lines.
• For each corner, measure the existing grade elevation at both the primary polygon and the offset polygon. Keep the lower value.
• Take the simple average of the kept corner elevations.
• Note on the drawings: “This calculation (averaging the corner elevations) is mathematically equivalent to the calculation procedure described in the Zoning Code: the code procedure first averages two corner elevations for each side, then averages the averaged exterior wall elevations – under the code procedure, each corner point is counted twice and divided by 2 to produce the final result, which is equivalent to simply averaging the corner elevations.”

Jurisdiction	Base Level Term	Method(s) Allowed
Seattle	Average Grade Level	Method A / Method B
Renton	Grade Plane	Method C