Meet the Massachusetts 2021 IECC Stretch energy code
An Overview of Insulation, Mechanical Equipment, and Design Strategies to Meet the Massachusetts 2021 IECC Stretch Code
The Massachusetts 2021 IECC Stretch Code mandates homes to meet specific HERS (Home Energy Rating System) Ratings for energy efficiency. Achieving these requirements, especially in a zone 5 climate like Massachusetts, is crucial for our energy future. This blog post provides insights into various specifications and design strategies that can help builders, designers, and homeowners meet or exceed code.
Transitioning to the 2024 Code
We are currently in a transition period, and by July 2024, the Massachusetts homes will need to meet even stricter criteria with a HERS Rating of <45. With lucrative utility rebates available to build all electric homes meeting this standard, now is an excellent time to envision and construct the 'house of the future.'
Recommended Specifications to Meet the 2021 IECC Stretch Code
Start in design
The most cost effective home starts in design. Create the spaces you need, not that your last home had; a custom design should enable a smaller home. Site the house to optimize solar gain (amazing this still needs to be said) . Don’t overdue the windows as they are expensive and responsible for a lot of heat-loss. Compact house with simple forms will always be less money to build efficiently over complex geometry. This includes reduced vaults/cathedrals, and less framing transitions such as dormers , overhangs, etc. Shade the windows - big eaves are good for building durability and reduced heat gain in the summer. Design matters more than ever! Check out one of our favorite books, Pretty Good House, that eloquently dives into design principals.
Insulation and Air Sealing
Components of the thermal enclosure - insulation and airbarrier:
Slab: R10 insulation under and around the slab's perimeter. See our detailed slab insulation resource.
Foundation Wall: Install R15 Thermax or equivalent on the entire interior foundation wall.
Rim/Band bays: R21 foam, 3”, to wrap over the bottom plate.
Exterior Walls: Aim for R21 insulation with sheathing as the primary air barrier. Add R6+ continuous insulation on the exterior for lower heating/cooling loads and reduced heat loss.
Windows: Choose good-quality double-pane windows with a U-value of 0.28 or lower. Fixed windows will typically have better performance specs for the same cost.
Attic Flat: R55+ cellulose insulation after fully air sealing the attic including wall top plates and chute vents.
Attic Hatch: R40+ rigid board to an airtight hatch; avoid pull-down stairs to vented attics.
Cathedral Ceilings: Ensure airtightness and grade 1 insulation- R50 is a good target, using 7” of closed cell foam or a mix of 3” closed cell foam + cavity insulation.
Attic Knee-Walls: Same as exterior walls, with the addition of 1-2” of continuous insulation on the attic side of the framing, detailed to be airtight.
Garage: As the garage is outside the thermal enclosure, it requires careful insulation and airtightness. Consider using 7" closed-cell spray foam (R49) or 3" closed-cell foam with a batt for framing cavities in the ceiling adjacent to conditioned space.
Heating/Cooling
For heating/cooling, heat pumps with a >9 HSPF and >19 SEER rating are recommended. There are many configuration options available from ductless, ducted, mixed and even air>water. Ensure accurate Manual J sizing calculations and choose equipment listed on the Mass Save QPL database.
Ducts and Ventilation
Keep all heating/cooling ducts inside the primary thermal enclosure to avoid penalties in the HERS rating and to avoid extremely tight duct tightness and testing requirements. Balanced ventilation with ERV or HRV is required by the 2021 IECC Stretch Code. See this page for an overview on balanced ventilation.
Hot Water and Appliances
Consider a heat pump hot water heater located in a fully insulated basement or in a mechanical closet in the main living area. Opt for energy-efficient appliances; refrigerators under 625 kWH and an Energy Star certified washing machine with matching dryer. Heatpump dryers are very efficient and increasingly propular.
Meeting the Massachusetts 2021 IECC Stretch Code requires careful planning and attention to various design elements, insulation, mechanical equipment, and ventilation. By starting in the home design phase and implementing the recommended specifications, code compliance will be achieved, rebates leveraged, and most importantly, the home will be durable, comfortable, healthy, and energy efficient.
Power House Energy Consulting offers flexible support to exceed Stretch Code requirements
We provide a design review with all of our HERS Ratings. Many projects benefit from an additional 1-2 hours of pre construction design support, to aid in mechanical system or ventilation system design. We can provide additional modeling to try various specs to meet over-code high performance rebate program requirements, or simply to explore assembly options. We give input on specific products, equipment, and simplified strategies to often reduce cost during construction as well as in the operation of the home.
Tell us about your project and how we can help you build a future read home!
