CS41 Energy Code Feasibility Study in Westborough, Massachusetts

Exterior Walls

R-30 spray foam insulation (3" closed cell spray foam + 2.5" open cell spray foam).

Slab

R-15 exterior perimeter insulation, 4ft deep.

Podium

Steel Frame Slab v1: R-30 batt insulation resting on drop ceiling,

Steel Frame Slab v2: R-30 closed cell spray foam insulation evenly coated over steel studs & cavity.

Post Tensioned Slab: R-30 continuous insulation on either side of the slab.

Note: Any of these options work.

Rim Joists

Seal interior rim cavity with minimum R-30 spray foam insulation (3" closed cell spray foam + 2.5" open cell spray foam).

Roof

Cavity Insulation: R-60 cavity insulation.

Roof Deck Insulation: R-45 continuous insulation at roof deck.

Note: Either of these options work.

Windows

Weighted Avg: U-0.24 / SHGC 0.30

Doors

Glazed: U-0.24 / SHGC 0.30; Opaque: U-0.21 (R-4.75);

Air Sealing

Units: ≤ 0.30 CFM50/ft² gross enclosure area; Use this protocol (click here).

Emergencies: If the two protocols above are not met, this can be used in case of emergencies, must be implemented immediately after drywall install (click here).

HVAC

Ducted forced-air system with a Navien NPE-240S2 combo boiler (96% adjusted efficiency, 196 kBtu/h) for heating.

Air source heat pump (SEER2 ≥ 16) for cooling.

Duct Sealing

The greater of 8 CFM/100 ft² conditioned floor area or 80 CFM (Duct Sealing Protocol)

HVAC Grading

Fan Flow Test: N/A

Watt Draw Test: N/A

Refrigerant Charge: N/A

Mechanical Ventilation

S & 1 Bed (Any): 50 CFM; 90% rated recovery; Any Climate; (Product Ref)

2 & 3 Bed: 70 CFM; 86% rated recovery; Any Climate; (Product Ref)

Local Mechanical Exhaust

Bathroom(s): ≥ 50 CFM intermittent & ≤ 3.0 sones OR ≥ 20 CFM continuous & ≤ 2.0 sones,

Kitchen (s): ≥ 100 CFM intermittent & ≤ 3.0 sones OR continuous, ≥ 5 ACH Based on kitchen volume & ≤ 1.0 sone.

Both: Exhaust directly outdoors, ENERGY STAR certified, utilize ERV to meet these requirements.

Thermostats

Programmable Thermostat (Product Ref)

DHW

Tankless natural gas water heater (Navien NPE-240S2) with a Uniform Energy Factor (UEF) of 0.96 (Product Ref).

DHW Piping

Supply piping insulated to R-3 minimum; Modeled pipe runs are optimized to 1/3 program default lengths; (Default Pipe Run = 2 x (CFA / Nfl)^0.5 + 10xNfl (CFA = conditioned floor area, Nfl = # conditioned floor levels)).

Water Fixtures

Watersense Certified Fixtures (Lavatory: ≤1.2 GPM, Shower: ≤2.0 GPM)

Refrigerator

All: ≤ 500 kWh annual usage; ENERGY STAR; Electric; (Product Ref)

Dishwasher

All: ≤ 240 kWh annual usage; ENERGY STAR; Electric; (Low Cost Product Ref) (Luxury Product Ref)

Clothes Washer

All: ≤ 136 kWh annual usage; ≥ 2.76 IMEF; ≥ 4.8 cubic ft capacity; ENERGY STAR; Electric; (Product Ref)

Clothes Dryer

All: ≥ 6 CEF; Ventless; Heat Pump Dryer; ENERGY STAR; Electric; (Product Ref)

Stove / Oven

Any Electric Stove; (Product Ref)

Lighting

100% high-efficacy (LED)

Solar Ready

Designated Solar Zone: Reserve a contiguous area equal to at least 40% of the total horizontal roof area (after excluding skylights, occupied decks, vegetated areas, and fire setbacks).

Contiguity & Obstructions: The zone must be free of all obstructions (pipes, vents, HVAC units) and maintain a minimum width of 5 feet.

Structural Capacity: Roof structures within this zone must be engineered to support a future collateral dead load of 5 PSF.

Orientation (Sloped Roofs): For roofs with a pitch of 4:12 or greater, the zone must be oriented between 110° and 270° of true north.

Electrical Infrastructure: Provide identified conduit pathways from the roof to the electrical service and reserve a labeled space for a dual-pole circuit breaker in the main panel or common space service.

EV Ready

Requirement: Provide EV Ready infrastructure for at least 20% of total parking. Provide a branch circuit and termination for the required spaces (up to 20% total), rated for a system capacity of at least 6.2 kVA per space.

HPWH Ready

N/A

Paperwork & Modeling

HERS / ERI Energy model, 2021 IECC checklists, ENERGY STAR MFNC checklists, and incentive documentation.

Testing & Verification

Unit Blower Door Test, Duct Test, Mechanical Ventilation Testing, Room Balancing, Slab, Predrywall & Final Inspection.

Exterior Walls

R-30 spray foam insulation (3" closed cell spray foam + 2.5" open cell spray foam).

Slab

R-15 - 4' deep exterior perimeter insulation.

Podium

Steel Frame Slab v1: R-30 batt insulation resting on drop ceiling,

Steel Frame Slab v2: R-30 closed cell spray foam insulation evenly coated over steel studs & cavity.

Post Tensioned Slab: R-30 continuous insulation on either side of the slab.

Note: Any of these options work.

Rim Joists

Seal interior rim cavity with minimum R-30 spray foam insulation (3" closed cell spray foam + 2.5" open cell spray foam).

Roof

Cavity Insulation: R-60 cavity insulation.

Roof Deck Insulation: R-45 continuous insulation at roof deck.

Note: Either of these options work.

Windows

Fixed: U-0.32 / SHGC 0.40

Operable: U-0.40 / SHGC 0.40

Doors

Glazed Entrance / Exit Doors: U-0.60 / SHGC 0.40;

Opaque: U-0.17;

Air Sealing

N/A

HVAC

ENERGY STAR min: SEER2 16 / HSPF2 8.2.

Duct Sealing

The greater of 8 CFM/100 ft² conditioned floor area or 80 CFM (Duct Sealing Protocol)

HVAC Grading

Fan Flow Test: N/A

Watt Draw Test: N/A

Refrigerant Charge: N/A

Mechanical Ventilation

Measured supply and outdoor air rates must meet ASHRAE 62.1-2019 minimums.

Local Mechanical Exhaust

Measured exhaust rates must meet ASHRAE 62.1-2019 minimums.

Thermostats

Programmable Thermostat (Product Ref)

DHW

Teal Systems / Raypak XTHERM 2005A Three boilers at 1,999 MBH each (5,997 MBH total), 96% thermal efficiency. Duplex Taco 1919 recirc pumps at 1.5 HP each (Pricing) (Product Ref).

DHW Piping

MA code and Energy Star DHW piping standards.

Water Fixtures

Watersense Certified Fixtures (Lavatory: ≤1.2 GPM, Shower: ≤2.0 GPM)

Appliances

Energy Star Certified / All-Electric.

Lighting

100% high-efficacy (LED) occupancy/vacancy sensors or auto controls in all common spaces (except lobby).

Solar Ready

Designated Solar Zone: Reserve a contiguous area equal to at least 40% of the total horizontal roof area (after excluding skylights, occupied decks, vegetated areas, and fire setbacks).

Contiguity & Obstructions: The zone must be free of all obstructions (pipes, vents, HVAC units) and maintain a minimum width of 5 feet.

Structural Capacity: Roof structures within this zone must be engineered to support a future collateral dead load of 5 PSF.

Orientation (Sloped Roofs): For roofs with a pitch of 4:12 or greater, the zone must be oriented between 110° and 270° of true north.

Electrical Infrastructure: Provide identified conduit pathways from the roof to the electrical service and reserve a labeled space for a dual-pole circuit breaker in the main panel or common space service.

EV Ready

Requirement: 20% of parking spaces; 40-amp dedicated branch circuit (or larger with ALMS); wiring suitable for ≥6.6 kW Level II EVSE, run to within 6 feet of each qualifying space.

HPWH Ready

N/A