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CAST architecture Modern Tudor DADU

Posted on Jun 2, 2022 in:
  • Case Studies

Vital Stats



Location: Seattle
Star Level: 4-Star
Checklist: 2018 Single-Family/Townhome Checklist
Verifier: Balderston Associates
Site and Water117
Energy Efficiency94
Health and Indoor Air Quality119
Material Efficiency75
 Total Score470

This modern Tudor Detached Accessory Dwelling Unit (DADU) demonstrates a way to add density to an existing neighborhood while honoring the historical design and character of its traditional Seattle community. Designed by CAST architecture, and built by Align Builders, the cottage is packed with plenty of Built Green features that integrate into its blending of modern and historical design details.

CAST architecture Modern Tudor DADU front facade

The interior celebrates values of beauty and shelter by the timbered and vaulted living area and comfortable flow of spaces through the kitchen and bedrooms downstairs. The Seattle code limits DADUs to 1000 sf, but the cottage gives the feeling of a spacious and comfortable 2-bedroom home.

Energy Efficiency

  • Wall insulation is the standard code R21, but the builder focused on executing the install to the HERS Grade 1 standards. This requires third-party inspection and batts that are evenly fluffed and filled with extra care to eliminate gaps and compressions.
  • The vaulted ceilings have R38 fiberglass batts.
  • Windows are low-e argon from Andersen.
  • Panasonic Intellibalance HRV installed to provide filtered fresh air directly to bedrooms and exhausts stale air while recovering about 80% of the heat energy.
  • The flush-mounted ceiling cassettes of the multi-head ductless heat pump system provides energy efficient space heating with unobtrusive design.
  • Low-flow toilet, sink, and shower fixtures.
  • ENERGY STAR appliances and 100% LED lighting.

Low-Impact Development and Rainwater Infiltration

The DADU occupies the existing home’s former back garden. The site included street access to both sides of the property, allowing for separate private entrances for both homes, and instantly integrating this DADU into the existing streetscape of the neighborhood. The bay window and arched front entry make it a familiar-looking addition for those walking around through the neighborhood.

There is no garage, but a side parking driveway is done with permeable paving stones. Also roof drainage is directed to infiltration trenches and pits so that it can be treated and infiltrated onsite. Landscaping is drought tolerant with only a small shared grass area that connects to the existing parts of the backyard.

CAST architecture Modern Tudor DADU dining kitchen
CAST architecture Modern Tudor DADU entry stair
CAST architecture Modern Tudor DADU DHP

Indoor Air Quality and Moisture Protection

The DADU emphasizes simple interior finishes with low toxicity and good ventilation for fresh air. Finish materials include a Strand Woven Poplar flooring from Ecotimber, and natural Marmoleum. The builder made sure to check that finish products, such as paints, caulks, and stains, were all low emitting and low VOC products. Paints used were Benjamin Moore “Aura” zero VOC products.

The exterior siding is installed over a HydroGap WRB that provides “rain screen” drainage. The lower-level stucco is also a water managed system. Window and door flashing details were checked on site for complete seals and physical drainage planes to ensure a very long-lasting wall system that prevents moisture-related damage and molds.

CAST architecture Modern Tudor DADU living room

Materials With Reduced Environmental Impact

The interior finish materials were not only selected for their low-chemical emitting properties to assist with healthy indoor air quality, but also for their environmentally friendly properties. The finished flooring materials selected were Cradle-to-Cradle certified carpets from Shaw and climate-positive Marmoleum. CAST’s most eco-friendly flooring selections were the ones they excluded, reducing resource extraction and pollution in the first place. They did this in two ways, first the exclusion of vinyl flooring, and the second by utilizing the lower floor’s concrete slab as the finished floor.

Locally produced cabinets from Canyon Creek meet low-VOC certification standards. Materials that were made with recycled content were used for the drywall, trim, doors, and cabinets. The builder tracked and reported recycling of job site waste, as all Built Green builders must do, and achieved at least a 75% diversion-from-landfill rate. To reduce toxicity Sill plates were borate-treated instead of using standard pressure-treated lumber.

CAST architecture Modern Tudor DADU back facade
CAST architecture Modern Tudor DADU lower entry


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