The City of Boulder, Colorado’s solar access regulation divides the city into three solar access areas to provide maximum solar access protection for each area, consistent with planned densities, topography, and lot configurations and orientations. The regulation then establishes solar fences in two of these solar access areas. Each solar fence completely encloses a lot in question, and its foundation is contiguous with lot lines. Further, solar fences are vertical, opaque, and lack any thickness. The regulation then forbids the construction of a structure on an adjacent lot that would shade a protected lot to a greater degree than the lot would be shaded by a solar fence, 12 or 25 feet in height (depending on solar access area), between two hours before and two hours after local solar noon on a clear winter solstice day. City of Boulder, CO, Code § 9-9-17.