I am currently working on a text amendment to possibly revise our exterior sideyard (side adjacent to a street) standards for our single-family zoning districts. Currently, we require the average setback along the shared frontage establishes the minimum required setback. This can get a little restrictive because gathering the info for averaging can be time consuming and, depending on the surroudning properties, the average could be skewed negatively, resulting in a significant reduction to the practical size of the buildable area. This usually occurs when a property's exterior sideyard is adjacent to front yards (which have a larger setback normally, especially in the older portions of the muni.)
I am toying with the idea of a strict percentage of lot width. Our interior sideyard setbacks standard is 10% of the lot width (on a 70' wide lot - 7' on each side of house), so I am thinking that a more appropriate percentage would be something that could account for sight lines across the corners, maintain an approximation of the setbacks along the shared frontage, and not be detrimental to the practical size of the buildable area.
Our minimum buildable lot width is 50 feet and typical is about 66-75 feet , so I am thinking that the percentage should be 20 or 25% of lot width.
What standards do you use, and what is the intent behind them (if you know)?