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Targa Homes: Shoreline 5-Star DADU

At first glance, this 5-star detached accessory dwelling unit (DADU) built by Targa Homes in the North City neighborhood of Shoreline appears to be a typical new home. But the materials, assemblies, and techniques used in its construction are anything but.

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.

Vital Stats

Section

Points

Location: Shoreline
Star Level: 5-Star
Checklist: Single-Family/Townhome
Verifier: Evergreen Certified
Site and Water 119
Energy Efficiency 149
Health and Indoor Air Quality 150
Material Efficiency 102
  Total Score 626
 

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.

Targa Homes: Shoreline 5-Star DADU finished exterior
Targa Homes: Shoreline 5-Star DADU exterior under construction
 

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.

Targa Homes: Shoreline 5-Star DADU living room
Targa Homes: Shoreline 5-Star DADU unfinished kitchen
Targa Homes: Shoreline 5-Star DADU finished kitchen
 

Built Green Highlights

Site and Water

  • Diamond Pier foundation system
  • Five of seven site trees preserved
  • Majority of 0.25 acre site left undisturbed
  • No site grading or clearing
  • Low-flow lavatory, showerheads, and kitchen fixtures
  • Transit-oriented development
  • All pervious hardscaping with a shared driveway

Energy Efficiency

  • Modeled to achieve 47% improvement over WSEC 2015
  • EnergyStar Homes Northwest Certified
  • Blower door tests resulted in 0.91ACH
  • Ultra-high efficiency electric water heating with 95% thermal efficiency
  • Provided roof area and rough-in conduit for future solar power wiring and controls

Targa Homes: Shoreline 5-Star DADU bedroom

Health and Indoor Air Quality

  • Indoor AIRplus Certified
  • Rainscreen installed under siding
  • High-efficiency pleated filter with MERV 13 used in ERV
  • Ductless mini-split and radiant heating
  • Dedicated shoe removal area at primary entrance

Materials Efficiency

  • Salvaged lumber from local deconstruction site used for siding, framing, and interior trim
  • Regionally produced framing and decking lumber, plywood, windows, millwork, siding, radiant panels, and drywall
  • Cork flooring
  • Open floor plan
  • FSC certified Pacific Madrone butcherblock countertop
  • Source separated and recycled all styrofoam and plastic sheeting

Targa Homes: Shoreline 5-Star DADU office

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