What is Boulder's solar access ordinance, and can it stop you from building?
The short answer
Boulder limits how much a new house or addition can shade the lots next to it. In Solar Access Areas I and II, new construction cannot shade a neighbor above an imaginary 12 or 25 foot fence on the property line between two hours before and two hours after solar noon on December 21. On steep or tight lots, it can decide how big a house can be.
Most buyers have never heard of these rules until they try to add a second story. Then it is the first thing their architect brings up.
How the rule works
The city assigns every lot to a solar access area based on its zoning. Area I covers the rural and low density residential zones, protected by a 12 foot solar fence. Area II covers most denser residential and mixed use zones, with a 25 foot fence. Everything else is Area III, with no fence. If a new building or addition in Area I or II would be taller than its fence, the owner submits a solar analysis with a topographic survey as part of the building permit.
Why it matters when you buy
If you are paying for a lot or a teardown, find out which solar access area it is in, and what the lots to the north allow, before you agree on a price. When you look at an existing hillside home, ask whether it could be built the same way today. Sometimes the answer is no, and that is part of what you are buying.
- City of Boulder, Solar Access Guide (read September 30, 2026)