According to the Carbon Leadership Forum’s Carbon Avoided Retrofit Estimator’s (CARE) website, “Renovating an existing structure typically has a much lower carbon footprint than building a new one because it reuses most of the carbon intensive parts of the building—the foundation, structure and building envelope.” Sylvan Court, which was originally constructed in 1964, recently underwent a renovation to upgrade the existing building instead of tearing it down; and also constructed a new building on the property’s former parking lot, doubling the amount of rentable housing units. While the original building doesn’t earn points on the new building’s checklist, their strategy was a great approach to minimizing their carbon impact, reduce waste, while still promoting urban density by constructing more units on the same lot.

The new building, a 20-unit apartment building, obtained a Built Green 4-Star certification on the 2017 multifamily checklist. The building was able to do so by claiming a variety of points throughout the checklist. Some of the highlight features utilized in the Built Green checklist to get the points were using drought-tolerant and native vegetation and low-flow plumbing fixtures to minimize the amount of water used on the property; BIBS insulation and a lower blower door score to keep energy costs down; low VOC paints, finishes, and interior products with indoor air-quality certifications to keeps tenants safe and healthy; and utilizing local and durable material to keep the building standing for a long time to come.

In addition to the variety of green features utilized by the construction team, the building offers bike storage with a repair station to incentivize tenants to ride their bikes or walk. The building is located within of the urban village zone and has a walkability score of 91. This in itself will help encourage more healthy living while reducing the need for a car.

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.