Energy Code & HERS Rating Guide
What Massachusetts energy codes mean for your ADU: HERS ratings, compliance tiers, testing requirements, and how to keep costs down.
What Is a HERS Rating?
A HERS (Home Energy Rating System) Index score measures a home’s energy efficiency on a 0–100 scale. The lower the score, the more efficient the building.
- HERS 100 = reference home built to 2006 IECC standards
- HERS 0 = a net-zero energy home
- Every 1-point decrease ≈ 1% less energy use
What it costs: A certified HERS Rater performs on-site testing (blower door, duct leakage, insulation inspection). Budget $500–$1,500 for ADU-scale projects.
HERS Index Scale
HERS 0Net-Zero
HERS 42New Home Target
HERS 52ADU Target
HERS 1002006 Baseline
Massachusetts Three-Tier Energy Code
Every MA municipality adopts one of three energy code tiers. The tier determines HERS rating requirements for all new construction, including ADUs.
HERS Requirement
Not required
- No HERS rating required
- Prescriptive compliance path
- Standard insulation & mechanical minimums
- Voluntary HERS rating accepted
North Shore: Danvers, Essex, Middleton
~50 towns statewide · Lower — no HERS testing needed
HERS Requirement
HERS 52 or better
- HERS rating mandatory for new construction
- Blower door & duct leakage tests
- ADU target: HERS 52 (mixed) or 55 (all-electric)
- ERV/HRV + EV-Ready wiring required
North Shore: Most municipalities
~245 towns statewide · +$500–1,500 for HERS testing
HERS Requirement
HERS 52 or better
- Builds on all Stretch Code requirements
- Homes >4,000 sq ft face additional reqs
- Stronger push toward all-electric
- Same ADU HERS targets as Stretch
North Shore: Beverly, Newburyport, Salem, Swampscott
~56 towns statewide · +$500–1,500 for HERS testing
HERS Targets for ADUs
ADUs receive more relaxed HERS targets than standard new homes, recognizing the challenges of very low scores in smaller buildings.
| Configuration | New Home Target | ADU Target | Difference |
|---|---|---|---|
| Mixed-fuel | 42 | 52 | +10 pts |
| Mixed-fuel + solar (≥4 kW) | 45 | 55 | +10 pts |
| All-electric | 45 | 55 | +10 pts |
| All-electric + solar (≥4 kW) | 48 | 58 | +10 pts |
Why the relaxed targets? Small buildings have less surface area relative to volume, making ultra-low HERS scores harder to achieve. Heat pump water heaters require adequate mechanical space that’s difficult to fit in compact ADU floor plans.
Clean Energy Credits
These measures earn HERS point credits that make compliance easier.
Solar PV
≥4 kW array
Offsets 3 HERS points for new ADUs; 5 HERS points for alterations, change of use, or fully attached additions.
Roof orientation matters — south-facing is ideal for maximum generation.
All-Electric
No fossil fuel connections
Offsets 3 HERS points for new ADUs; 5 HERS points for alterations, change of use, or fully attached additions.
Heat pumps for both HVAC and hot water — no gas line simplifies construction.
Embodied Carbon
Low-carbon materials
Added Feb 2025 (225 CMR 22 §R406.5.2): 3-point credit for low-GWP concrete (requires EPD from plant) or insulation with net GWP ≤ 0.
Ask your concrete supplier about Environmental Product Declarations (EPDs) — low-carbon mixes are increasingly available in MA.
Example: An all-electric ADU with 4 kW solar starts at HERS 58 instead of 52 — compliance becomes significantly easier.
How Equipment & Appliances Affect Your HERS Score
Not all equipment carries equal weight. Here’s what moves the needle most when targeting HERS 52 in a North Shore ADU, ranked by impact.
| Category | HERS Impact | Recommendation | Cost |
|---|---|---|---|
| HVAC System | 10–12 pts | Ductless mini-split heat pump, cold climate certified, HSPF2 11+ | $3,500–$7,500 (single-zone) |
| Water Heater | 6–8 pts | Heat pump water heater (HPWH), UEF 3.0+ | $3,000–$4,500 installed |
| Ventilation (ERV/HRV) | 2–3 pts | ERV with ≥0.5 W/CFM, 75%+ ASRE | $2,000–$3,500 installed |
| Kitchen & Laundry Appliances | ~2 pts | All ENERGY STAR — induction range if going all-electric | +$500–$1,500 over standard |
| Lighting | ~1 pt | 100% LED fixtures throughout | +$200–$500 |
| Solar PV | ~6 pts total | ≥4 kW array for MA credit + generation offset | $10,000–$14,000 for 4 kW |
HVAC System
Ductless mini-split heat pump, cold climate certified, HSPF2 11+
- Single largest driver of the HERS score
- Ductless eliminates duct losses entirely
- Must be ENERGY STAR Cold Climate Certified
- HSPF2 matters more than SEER2 in MA’s heating-dominant climate
Mass Save: $250/ton up to $2,500 for new construction. Up to $8,500 when replacing existing heating. Must be ENERGY STAR Cold Climate certified.
Water Heater
Heat pump water heater (HPWH), UEF 3.0+
- Second-largest equipment driver for HERS
- 3–4x more efficient than a standard gas tank
- Needs ~700 cu ft of surrounding air volume
- Plan the mechanical closet early — retrofitting is expensive
Mass Save: $750 instant rebate ($1,500 for split systems). Income-eligible households may qualify for no-cost installation.
Ventilation (ERV/HRV)
ERV with ≥0.5 W/CFM, 75%+ ASRE
- Mandatory as of February 2025 — exhaust fans no longer qualify
- ERV preferred over HRV for MA climate (transfers heat + moisture)
- Requires dedicated supply and exhaust ductwork
- ~$90–$100/year operating cost
Plan ceiling/wall duct routing during framing.
Kitchen & Laundry Appliances
All ENERGY STAR — induction range if going all-electric
- Fridge, dishwasher, range, washer, dryer are all modeled in HERS
- ENERGY STAR specs outperform RESNET defaults by ~2 pts combined
- Induction cooktop is required for the all-electric credit
- Heat pump dryers are more efficient but have smaller individual impact
Specify “ENERGY STAR” on plans — exact models can be chosen later.
Lighting
100% LED fixtures throughout
- HERS model assumes ~80% LED for new construction
- Specifying and verifying 100% LED gives a reliable improvement
- Lowest-effort, highest-certainty upgrade you can make
No reason not to spec 100% LED in new construction.
Solar PV
≥4 kW array for MA credit + generation offset
- Directly offsets modeled energy consumption in HERS
- MA grants additional 3-pt credit at ≥4 kW
- 6 kW+ array can yield 10+ pts — approaching net-zero for small ADUs
- Best “safety valve” if struggling to hit HERS 52 through envelope alone
Can be installed on ADU roof or principal dwelling’s roof.
Not Factored into HERS
EV-Ready Wiring: Mandatory code requirement but not modeled in HERS. Budget $500–$1,500.
Range Hood / Cooking Ventilation: Not in HERS, but high-CFM hoods for gas ranges complicate air sealing (which IS in HERS).
Smart Thermostat: Valuable for actual savings, but RESNET does not currently credit it.
Exterior Lighting: Only interior fixed lighting is modeled in HERS.
The All-Electric ADU Path (Recommended)
Going fully electric relaxes your HERS target from 52 to 55 and eliminates the $2,000–$5,000 cost of running a gas line. A mini-split + HPWH + induction range + ERV gets you well within the 55 target.
Budget Reality Check
Energy-related equipment for HERS 52 typically adds $12,000–$20,000 over a minimal baseline. After Mass Save rebates ($750 HPWH + up to $2,500 heat pump for new construction), the net additional cost reduces to roughly $9,000–$17,000. Income-eligible households may qualify for up to $16,000 in enhanced rebates.
What the HERS Rater Tests
Blower Door Test
Measures air leakage of the building envelope
Duct Leakage Test
Verifies HVAC duct sealing meets targets
Insulation Inspection
Thermal bypass checklist to confirm coverage
Equipment Verification
Confirms HVAC, water heater, and appliance efficiency ratings
2025 Code Updates
The MA DOER amended the Stretch and Specialized Energy Codes effective February 14, 2025, based on 18+ months of stakeholder feedback.
ERV/HRV Required
Energy Recovery Ventilator (ERV) or Heat Recovery Ventilator (HRV) now required — bathroom exhaust fans alone no longer qualify.
EV-Ready Wiring
1 EV-Ready parking space with wiring required per dwelling unit.
Heat Pump Water Heater
The most challenging ADU requirement — needs adequate interior mechanical space with sufficient air volume.
What This Means for Your ADU
Danvers, Essex, Middleton
- No HERS rater needed
- Follow prescriptive energy code path (IECC 2021 w/ MA amendments)
- Must still meet insulation, window, and mechanical minimums
- Lower compliance cost overall
Most North Shore municipalities
- Must hire a certified HERS Rater — budget $500–1,500
- Target HERS 52 (mixed-fuel) or 55 (all-electric)
- Plan mechanical space for heat pump water heater early
- Going all-electric earns a 3-point offset
Beverly, Newburyport, Salem, Swampscott
- Same HERS targets as Stretch for ADUs under 900 sq ft
- Additional requirements apply to larger projects
- Stronger push toward all-electric construction
- Check with local building department for amendments
North Shore Town Energy Code Tiers
(4)
(18)
Source: MA DOER, December 2025
Need Help with Energy Code Compliance?
We build to Stretch and Specialized standards across the North Shore. Let us handle the compliance details.