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 |
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