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Model Remodel - Columbia City DADU

DADU Model Remodel
Vital Stats
Location: Seattle
Star Level: 4-Star
Checklist: Single-Family/Townhome
Verifier: Tom Balderston
SectionPoints
Site and Water101
Energy Efficiency87
Indoor Air Quality121
Material Efficiency95
Total Score503

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A new DADU (Detached Accessory Dwelling Unit) demonstrates creative ways to add density to an existing neighborhood, along with plenty of Built Green features. Designed by architect Sheri Newbold at live-work-play and built by Model Remodel, the project includes a new garage with a studio apartment and deck above that fit neatly into the backyard garden just four blocks from the center of Columbia City. 

Energy Use

The project shows how a well-insulated home can make use of affordable systems to achieve the Built Green 4-Star level and exceed the requisite 20% energy savings compared to 2012 Washington State Energy Code. The energy performance stems from several relatively low-cost upgrades:

  • Wall insulation is upgraded to R28 using a "Blown in Blanket" system and 1-inch polyiso rigid exterior foam with a vented rain screen siding detail. 
  • Roof insulation is an R52 hybrid spray foam and batt system that requires no roof vents.
  • Windows have a .28 U-value, while large trees were preserved to keep large glass areas from overheating in the summer.
  • Very tight air sealing with a blower door test of 2.8 ACH @ 50 Pa.
  • Panasonic Whisper Comfort spot ERV fan in the bathroom.  
  • Infrared radiant electric ceiling panels from Mighty Energy Solutions create a very simple heat system that gives instant comfort and better zoning. 
  • Low-flow devices on sink and shower fixtures for reduced energy use and water savings.
  • ENERGY STAR appliances, 100% LED lighting, and a sunlight tube in the bath area. 


Low Impact Development and Rainwater Catchment

A lot of care was taken by the builder to fit the structure into the existing backyard. Two large trees were protected and grow nicely around the completed structure. The owners completed the landscaping themselves with an emphasis on drought tolerant and native plants. The existing landscaping was disturbed very little. 

The site has infiltration trenches for the roof water drainage, so it will continue to supply the trees' root systems. 

To further reduce water use, the toilet is a dual flush 1.0 gallon single flush model by TOTO paired with a low flow sink and shower fixtures.

Indoor Air Quality and Moisture Protection

The studio emphasizes simple interior finishes with low toxicity and good ventilation for fresh air. The foam insulation near the outer surface of the walls and roof helps provide a more airtight shell and protects the structure from possible condensation. There are no carpets, which reduces the buildup of indoor pollutants and makes the home easier to clean. 

Model Remodel took a lot of care to ensure good air sealing between the house and garage and to prevent any fumes from getting into the living space. At the time of the blower door test, a pressure differential test showed only a 48 Pa relative pressure in the garage, which is an excellent result - it shows a very tight separation between the living unit and the garage. 

The builder does a lot of checking on products, paints, caulks, and stains to make sure they are all low emitting and low VOC products.  Paints used were Ben Moore "Aura" zero VOC. 

Whole house ventilation from a central Panasonic Whisper comfort fan ensures a balance of fresh air and exhaust with heat recovery. 

The exterior siding is installed over a rain screen space. Window and door flashing details were checked on-site for complete seals and physical drainage planes to ensure a very long lasting wall system. The roof is sealed with a heat-welded TPO membrane.

Materials with Reduced Environmental Impact

The materials used include recycled cabinets from Second Use Building Materials, recycled content siding from Boral, along with drywall, lumber, and doors containing recycled content. Additional materials include a strand-woven poplar flooring from Ecotimber and Marmoleum.

The builder tracked and reported recycling of job site waste, as all builders do on Built Green projects, and achieved a 75% diversion rate. 

live-work-play and Model Remodel have shown an elegant path to backyard living with this unique project. DADUs can provide an option for flexible and multi-generational living or serve as an additional source of income for owners.

 

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    Use pervious surfaces to reduce rainwater runoff