Does an ADU Need HERS Registration?
It depends on the measures the design relies on. Where any of them require field verification, the compliance forms are registered with a HERS provider and a rater has to verify the work on site.
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What registration means
Some Energy Code measures cannot be certified on paper alone — they have to be tested or inspected in the finished building. Where a design relies on one of those, the compliance documents are not simply printed and signed. They are completed through an approved data registry operated by a Home Energy Rating System provider, and the registry issues them with a registration number that ties the paperwork to the project.
Who does what
The design-stage certificate identifies which measures will need verification. During construction, the installing contractors complete their Certificates of Installation. A third-party rater then carries out the tests and completes the Certificate of Verification, and the result is reported to the registry as a pass or a fail. A failed verification has to be corrected and re-verified; it is not a paperwork formality.
When an ADU avoids it
Not every ADU needs a rater. A small unit served by equipment that does not depend on verified measures — a ductless heat pump rather than a ducted system, for instance — can often be documented without field verification at all. That is a design decision as much as a compliance one, and it is worth taking deliberately: choosing a system that avoids verification removes a scheduling dependency from the end of the build.
Where verification is unavoidable, the thing that causes trouble is discovering it late. A rater has to be engaged and the tests scheduled before the building is closed up and signed off, so the requirement is better identified at design stage than at final inspection.