What is HERS testing and when is it required?

HERS testing is independent, third-party field verification of certain energy measures by a certified HERS (Home Energy Rating System) rater. Where it is required, the rater inspects and tests the installed work and signs off on the CF3R (Certificate of Verification) — confirming that what was actually built matches what the Title 24 report assumed.

How HERS fits the compliance lifecycle

HERS verification is the construction-stage backstop to the design-stage CF1R. The three documents work in sequence:

1. CF1R — the design-stage Certificate of Compliance prepared with your permit set.
2. CF2R — the Certificate of Installation completed by your contractors as equipment goes in.
3. CF3R — the Certificate of Verification completed by an independent HERS rater for measures that require field testing.

The HERS rater is independent of the contractor on purpose, so the verification is impartial.

When HERS testing is typically required

The exact triggers depend on your design and code cycle, but HERS verification commonly applies to measures that can only be confirmed in the field, such as:

• Duct leakage — when the ADU has a ducted HVAC system, duct sealing is often HERS-verified.
• Refrigerant charge / airflow — for certain ducted systems, depending on equipment and zone.
• Building envelope air leakage — where a blower-door test is required by the chosen compliance approach.
• Specific performance-path credits — measures the energy model relied on may need HERS confirmation.

Many compact ADUs designed around a ductless mini-split heat pump avoid some duct-related HERS tests simply because there is no duct system to verify — one reason ductless systems are popular in ADU design. This is design-dependent, not a guarantee.

What this means for your project

HERS testing happens after your plans are approved and the systems are installed — it is not part of preparing the report itself, and you arrange the rater (or your contractor does) during construction. What we do at the plan stage is make sure the CF1R clearly identifies which measures will require HERS verification, and that the mechanical and other sheets are designed so those measures can pass.

Because the specific tests required, and any exemptions, depend on your design and jurisdiction, the applicable code cycle and local amendments vary — confirm with your local building department. We prepare the registered CF1R noting the applicable HERS measures as a +$240 Title 24 add-on alongside your MEP plans; see Title 24 Reports.