HERS Rating Chelmsford, MA — Specialized Energy Code Town

Official Maximum HERS Index Scores (Table R406.5)

These are the official maximum HERS Index scores that apply to projects in Chelmsford under Table R406.5 of the current code (2025 DOER Technical Guidance):

Scores are measured before counting on-site renewable generation (per R406.5). Historic buildings may opt out for alterations under R503.1.1. Embodied-carbon credits (+3 points) come from low-GWP concrete and insulation EPDs per Table R406.5.3/R406.5.4.

Complete Stretch Code Compliance Requirements in Chelmsford

Beyond the HERS maximums above, every new dwelling in Chelmsford on the HERS pathway must satisfy four code sections — R403.6 (Ventilation), R404.4 (EV Ready), R406 (HERS) and Appendix RB (Solar Ready) — per the 2025 DOER Technical Guidance:

• Balanced mechanical ventilation (R403.6): an ERV or HRV system meeting minimum system airflow, heat/energy-recovery efficiency, fan sound ratings and regulated air-inlet and exhaust locations — verified by field testing.
• EV-Ready parking (R404.4): pre-wiring with a connection point and dedicated electrical panel capacity for future vehicle charging.
• Solar-Ready roof (Appendix RB): a dedicated solar zone with structural-load verification, an electrical interconnection pathway and reserved panel space — unless the project installs solar directly.
• Air-tightness & duct sealing: blower door result of 3.0 ACH50 or lower (Climate Zone 5) and duct leakage within 4 CFM25 per 100 sq ft.

Passive House alternative (R405): Phius or PHI certification satisfies the code in Chelmsford in place of a HERS score — with a Certified Passive House Consultant for design and a Phius Certified Verifier/Rater during construction — and still requires EV-Ready and Solar-Ready compliance. Prescriptive path: allowed only for buildings without individually separate dwelling units, additions, and alterations — and a whole-building prescriptive project must implement 2 of the 3 additional-efficiency packages in R408 (enhanced envelope, higher-efficiency HVAC, or reduced water-heating energy). Additions of 1,000 sq ft or more (or exceeding 100% of the existing floor area) must meet both R502.3 prescriptive and the R406.5 HERS limits. Level III alterations (work area over 50% of the home and over 1,000 sq ft) also trigger HERS compliance; historic buildings are exempt under R501.6. Note that ENERGY STAR® is no longer a compliance path — HERS and Passive House are the two certification routes in Chelmsford.

Chelmsford’s Specialized Code: Three Ways to Comply (Appendix RC)

1. Zero Energy Pathway (RC102): certify HERS 0 or lower — the home produces as much energy as it uses. Before counting on-site solar, the design must still score ≤45 (all-electric) or ≤42 (mixed-fuel) and meet IECC 2021 envelope U-factors. Alternative: Passive House plus a Phius ZERO design certification — the only Specialized option that can credit off-site renewable energy.
2. All-Electric Pathway (RC103) — the most common route in Chelmsford: comply with the R408.2 HVAC and water-heating efficiency packages (electric-resistance primary heating is excluded — heat pumps required), meet EV-Ready and Solar-Ready, then either achieve a final certified HERS of 45 or less without on-site power (with ERV/HRV, R406.2 lighting, and base-code U-factors) or pre-certify to Phius CORE / PHI. With load-management design, most all-electric homes run on a standard 200-amp panel.
3. Mixed-Fuel Pathway (RC104) — only for dwellings under 4,000 sq ft: score HERS 42 or less without on-site power, plus electric-readiness (RC104.3), on-site renewables (RC104.4/RC105) and EV-Ready — or pre-certify Passive House with electric readiness. Electric readiness in Chelmsford means a 250-volt/40-amp outlet within 3 feet of any gas or propane range, a 250-volt/30-amp outlet within 3 feet of the clothes dryer, a reserved branch circuit for a future heat-pump heating system, and a heat-pump water-heater location with 7-foot clearance.

Detail sourced from the 2025 Massachusetts Stretch & Specialized Codes Technical Guidance (DOER, Sept 2025), Table R406.5 and Appendix RC.