With a specific focus on indoor air quality, this home employs a new ventilation and air filtration system, helping to make it a safe and comfortable environment for its occupants. The state-of-the-art fresh air system includes a Zehnder 350 HRV, Zehnder ComfoPost inline heating/cooling coil, and HEPA air filtration system. This system allows for fresh, filtered air to enter the home throughout the day and to be increased when needed, such as when the kitchen hood fan is drawing smoke out of the kitchen during cooking. This fresh air system maintains high indoor air quality by reducing particulates in the air, even when the outdoor air quality is particularly poor, such as during a summer forest fire.

Built with passive and active solar needs in mind, this two-story house faces south. Triple-paned Vinvltek windows on the south side provide passive heating and natural light within the home. White interior paint also helps provide significant daylighting and reduces energy demand from the home’s LED lighting.

The home also employs a 12.87kW photovoltaic system, producing enough power to make the home net positive and power an electric vehicle. With a shell system constructed from 6.5” SIPs walls, 10.25” SIPs roof, 4” foam under the slab-on-grade, ICF form slab-edge stemwalls, and U 0.18 average triple pane windows, this house has a tight envelope, helping to reduce energy consumption.

The three-bedroom, two bath house is meant to allow the occupants to age in place. The first floor has a kitchen, main living space, a bedroom and bathroom, and ADA-compliant doorways.

Overall, this home is a comfortable, clean, net positive building, allowing the homeowners to be happy, healthy, and confident in the knowledge that their home is serving their needs, meets a high standard of excellence, and is protecting the environment in the process.

The exterior of the house showcases local materials chosen for their durability and style. An 8.9 kW solar array brings the home close to net-zero annual energy consumption. The garage has been pre-wired for an EV charger. The attractively landscaped lot uses all native plants and bucks the suburban tradition of a water- and chemical-consuming lawn.

Passive solar features make the interior light and bright. The mini-split heat pump, SIPS walls, triple-paned windows, and the super-insulated slab and ceilings help keep the home comfortable year-round. The concrete slab was polished and sealed, requiring no additional flooring materials on the lower floor. WaterSense certified plumbing fixtures were used throughout to reduce water consumption without sacrificing functionality.

Built Green Highlights

Site and Water

• No lawn
• Landscaped with native plants
• Hydro-zoned landscape design
• All WaterSense-certified plumbing fixtures

Energy Efficiency

• EnergyStar certified
• Mini-split heat pump
• HERS score = 11
• 8.9 kW solar array
• All LED lighting
• Triple-paned windows

The defining feature of the project is the extensive use of 100+ year old reclaimed lumber, deconstructed from local buildings by Sledge Seattle. While the use of reclaimed lumber is becoming more common in finish applications, this home was framed with +90% reclaimed fir. Reclaimed 1x5 material with characteristic nail holes and patina can also be seen on the front facade and interior accent walls.

Despite its antique skeleton, this DADU was built to modern high-performance standards, resulting in energy consumption modeled 47% lower than an equivalent code-built home. Airtight construction was facilitated by AeroBarrier to passive house level (0.044 CFM/SF). This is of course paired with balanced ventilation by an ERV that brings in just the right amount of fresh, filtered air and exhausts stale air 24 hours a day. Other mechanicals in this all-electric home include a hybrid (heat pump) water heater, ductless heat pump, and electric radiant heat panels mounted on the bedroom ceilings.

To minimize site disturbance and accelerate the schedule, the home was built on a Diamond Pier foundation that was installed single-handedly in about 5 days. Diamond Piers are a type of pin pile that require no excavation and won’t impact underground hydrology.

 

Since the majority of reclaimed wall studs are 2x4s, the wall assembly includes a 2” continuous layer of mineral wool on the exterior of the sheathing. The unvented roof also has a layer of graphite EPS (GPS) rigid foam above the sheathing. Targa Homes set a goal to minimize the amount of foam used in construction and the roof represents the vast majority of it.

Interior finishes were chosen with an emphasis on sustainability and indoor air quality. Comfortable cork flooring runs throughout the home and sustainably sourced Madrone butcher block counters were chosen for the kitchen. All paint and coatings are low- or zero-VOC.

During construction, Targa Homes meticulously source-separated waste, including thorough plastic film and styrofoam recycling.

The homeowners decided to move into the DADU and rent out their main house. So far, they love living in their Built Green® certified home.