How to calculate the solar zone area
It’s true: Solar-ready buildings are mandatory through either the prescriptive or performance compliance pathways in the Energy Code.
Nonresidential solar-ready requirements apply to the following:
- High-rise multifamily buildings with 10 or fewer stories
- Motel/hotel occupancies with 10 or fewer stories
- All other nonresidential buildings with 3 or fewer stories
There are two available methodologies to determine the minimum solar zone area:
Method 1 is based on total roof area.
The “solar zone” equals total roof area minus skylight area. To comply with the Code, it must be 15% of the total roof area or greater.
Solar zone = Total roof area – Skylight
Solar zone = >15% total roof area
Method 2 calculates the potential solar zone.
In this method, the minimum solar zone area may be reduced if the building site is shaded (by objects like mature trees or nearby buildings that are not a part of the subject building). There must be no other access to unshaded roof area that could fit the full solar zone.
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Solar Insolation Without Shading
Obstructions (i.e., roof mounted equipment, vents) cannot be located within the solar zone, either. This ensures that the solar zone is clear and open, so that a solar energy system can be installed later. Additionally, obstructions must be located at a sufficient horizontal distance away from the solar zone so that they will not shade the zone.
The horizontal distance (D) from the obstruction to the solar zone must be at least two times the height difference (H) between the highest point of the obstruction and the horizontal projection of the nearest point of the solar zone..
Obstruction = D ≥ 2H
This image is very common to illustrate solar zone requirements. What is important to note is that the dormer does not look compliant, its height is too high (H) for its distance from the array (D). At right, the vent appears compliant with the Code.
For personalized help with your solar zone calculation, contact an Energy Code Coach anytime. Call us at (805) 781-1201 or submit a help request on our site.
Resources are available to help you navigate code changes on the California Energy Commission website and 3C-REN Energy Code Connect Resource Library.
