Introduction to Zero Energy Ready Homes

Zero energy ready homes are designed to be highly energy-efficient, aiming to minimize energy consumption and maximize the use of renewable energy. The concept builds on the idea of conserving energy as much as possible and then adding renewable energy sources, such as solar panels, to achieve a balance where the home produces as much energy as it consumes.

The Path to Zero Energy

In 2014, it was estimated that 70% of the journey to achieving net zero energy homes could be accomplished through conservation measures alone. This approach has been largely validated over time. The 2021 International Energy Conservation Code (IECC) aligns with the Department of Energy's Zero Energy Ready Home Program (ZERH), ensuring that new homes built to this code are close to achieving zero energy status. Additionally, building to this code can qualify homeowners for Section 45L Tax Credits.

Construction Requirements for Zero Energy Ready Homes

Climate Zone 2A: Unvented Attic and Spray Foam Insulation

In Climate Zone 2A, homes use an unvented attic with spray polyurethane foam at the roof deck. This spray foam can be either open-cell or closed-cell, with closed-cell foam offering better wind uplift resistance, especially in hurricane-prone areas. Advanced framing techniques using 2x6 studs at 24 inches on center are employed, reducing material costs and labor.

Climate Zone 3B: Unvented Attic and Monolithic Slab on Grade

For homes in Climate Zone 3B, the insulation is placed on the underside of the roof sheathing in unvented attics. This assembly does not require venting or vapor diffusion ports if tile roofing is used. The walls are framed similarly to Zone 2A, using 2x6 studs at 24 inches on center with rigid foam insulation on the exterior to manage inward vapor drive.

Climate Zone 4C: Vented Attic and Conditioned Crawl Space

In Climate Zone 4C, a vented attic with a conditioned crawl space is common. The assembly involves a continuous air control layer created by sealing gypsum board at the ceiling. The exterior walls include R-10 rigid insulation to control condensation, with no interior vapor barrier, allowing for drying to the interior.

Climate Zone 5C: Unvented Roof and Vented Crawl Space

Homes in Climate Zone 5C feature unvented roofs with rigid foam insulation at the roof deck to control condensation. Advanced framing with 2x6 studs at 24 inches on center is used, with additional rigid foam on the exterior walls to manage vapor drive.

Climate Zone 6: Vented Over Roof and Interior Insulated Basement

For Climate Zone 6, a vented over-roof is used to control ice damming. The ceiling and wall assemblies do not include an interior vapor barrier but use a Class III vapor retarder. Rigid foam insulation at the roof deck and on the walls helps control condensation and meet energy efficiency codes.

Climate Zone 7 and 8: Vented Cathedral Ceiling and Interior Insulated Basement

In the coldest climates, Zones 7 and 8, vented cathedral ceilings with rigid foam insulation are employed to manage moisture and vapor. The exterior walls use rigid foam insulation to prevent condensation within framing cavities. The assembly must also include provisions for adequate ventilation to handle ice damming.

Conclusion

Building zero energy ready homes involves integrating advanced construction techniques and materials to achieve high energy efficiency and sustainability. By adhering to the 2021 IECC and employing specific construction methods tailored to various climate zones, a general contractor can ensure that homes are not only energy-efficient but also qualify for significant tax incentives. This approach paves the way for a future where homes contribute positively to environmental sustainability.

Source: Lstiburek, Joseph W. "What Does 'Zero Energy Ready' Homes Mean?" ASHRAE Journal, vol. 65, no. 12, Dec. 2023, pp. 12+