ZeroZero House

(Zero Embodied Carbon + Zero Operational Carbon)

A Net Zero home creates as much on-site renewable electricity as it consumes over the course of one year. However, what Net Zero fails to take into account is the Embodied Carbon of the materials required to build the home in the first place (i.e., the carbon emissions released when mining raw materials, manufacturing them into building products, shipping these products to site, and installing them). The Embodied Carbon of even a modest 1,200 SF home is an average of 23 tons of CO2e [1], which is the equivalent of driving a gasoline car 62,630 miles, or 2.5 times around the world [2].

 

ZeroZero House is a case study to show how a new home can not only be Net Zero, it can also have Zero Embodied Carbon - without having a significant impact on either the design or the construction cost [3]. With new design tools like BEAM [4], planning for a Zero Embodied Carbon home has never been simpler.

 

ZeroZero House is a 2-story detached Accessory Dwelling Unit (ADU) that has a self-contained 2-bedroom residence on the 2nd floor, and a 2-car garage on the ground floor that can later be converted into an aging-in-place 2-bedroom apartment.

Design Strategies:

  • Efficient Building Footprint

  • Efficient Organization of Space

  • Future Flexibility (Aging-in-Place Ground Floor Apartment)

  • Tight Thermal Building Envelope for Energy Efficiency

  • Healthy Indoor Air Quality (All-Electric Equipment & Appliances, Induction Cooktop, ERV Mechanical Ventilation, and Non-Toxic Material Selections)

  • Frost-Protected Shallow Foundations to Reduce Excavation Costs for deep foundations and to Reduce the Quantity of Concrete – a main contributor of CO2e in new construction (often accounting for a 1/3rd of the building’s lifecycle carbon footprint).

  • Heat Pump Space Heating/Cooling and Water Heating

  • Minimize the size of the rooftop PV array required to achieve Net Zero

Key Material Selections:

  • Foundations: Frost-Protected Shallow Foundations (FPSF) to reduce excavation and concrete quantity

  • Concrete: >50% SCM mix (no cost premium over regular mix)

  • Sub-slab Insulation (R-10): 2” DuPont Styrofoam ST-100 (Material Price: $1.03 /SF [$0.52 /SF per inch thickness]; Compare with 2” Owens Corning Foamular 250 R-10: $1.75 /SF [$0.88 /SF per inch thickness])

  • Below Grade Insulation (FPSF vertical & horizontal insulation, R-10): 2” DuPont Styrofoam ST-100 (Material Price: $1.03/SF [$0.52 /SF per inch thickness]; Compare with 2” Owens Corning Foamular 250 R-10: $1.75 /SF [$0.88 /SF per inch thickness])

  • Exterior Wall Structure: 2x6 Wood + 1/2” plywood sheathing

  • Exterior Wall Insulation (cavity, R-20.4): Cellulose Dense Pack, R-3.7 /in. (Installed Price: $11 to $12.65 /SF [$2.00 to $2.30 /SF per inch thickness], www.homeadvisor.com; Compare with 3” Closed-Cell Spray Foam Insulation, R-7 /in. $3.00 to $4.50 /SF [$1.00 to $1.50 /SF per inch thickness]; www.homeadvisor.com)

  • Exterior Wall Insulation (continuous, R-5.4): 2” Wood Fiber Board, R-2.7 /IN.

  • Exterior Wall Cladding: 3/4” MOSO Bamboo X-Treme Outdoor Pre-finished Shiplap Siding

  • Drywall: 5/8” USG EcoSmart Firecode (Material Price: $0.33 /SF; Compare with USG Firecode $0.33 /SF)

  • Windows: Anderson Fibrex PVC-clad Wood, Double-Glazed

  • Floor Structure: TJI Wood Joists

  • Flooring: 1/2” x 3-3/4” Solid Bamboo (Material Price: $2.99 /SF; Compare with 3/4” x 3-1/4” Solid Oak $4.44 /SF)

  • Flooring: Porcelain Tile

  • Ceilings: 1/2” Drywall CertainTeed AirRenew (Material Price: $0.33 /SF; Compare with 1/2” USG UltraLight $0.29 /SF)

  • Roof Structure: 2x12 Wood + 5/8” OSB Roof Decking

  • Roof Insulation, cavity (R-41.6): 11-1/2” Cellulose Dense Pack, R-3.7 /in. (Installed Price: $23 to $26.45 /SF [$2.00 to $2.30 /SF per inch thickness], www.homeadvisor.com; Compare with 6” Closed-Cell Spray Foam Insulation, R-7 /in. $6.00 to $9.00 /SF [$1.00 to $1.50 /SF per inch thickness]; www.homeadvisor.com)

  • Roof Insulation, continuous (R-8.1): 3” Wood Fiber Board, R-2.7 /IN.

  • Roofing: Asphalt Shingles Owens Corning, Supreme

Footnotes:

[1] Builders for Climate Action (www.buildersforclimateaction.org) conducted a survey of 550 homes in Canada using their BEAM calculator. For an equivalent 1,200 SF home, the results showed the embodied carbon of the homes ranging from 10 tons to 66 tons CO2e, with the average being 23 tons of CO2e.

[2] 23 tons CO2e is the equivalent of 2,588 gallons of gasoline. The US Environmental Protection Agency (EPA) reports that the CO2 emissions from a car burning a gallon of gasoline is 0.008887 tons CO2 /gal. EPA (“Greenhouse Gas Emissions from a Typical passenger Vehicle, 2014, https://bit.ly/2HAwL5p). The Average fuel economy of a car is 24.2 mi/gal (https://afdc.energy.gov/data/10310). The circumference of the earth is 24,901 mi.

[3] The top contributors of CO2e in new construction are concrete (~33% of the total building’s carbon footprint), insulation (~26%), and cladding (~13%). There are many low-hanging fruit decisions that can have zero-to-little impact on cost, particularly with regard to the types of concrete mix, insulation and cladding. Where possible, we have provided the estimated cost per SF of materials and, for comparison, an equivalent “standard” material cost pf SF.

[4] Created by Builders for Climate Action, BEAM is an easy-to-use calculator that quantifies the embodied carbon of building materials. The data is sourced from Environmental Product Declarations (EPD). EPDs summarize the lifecycle assessment of a material, follow the ISO 14040 standard, and their results are third-party verified by well-known organizations like ASTM, NSF and UL-Certified.