This project in Bellingham's Lettered Streets neighborhood is one of the highest-performing DADUs Fox Lake Builders has completed in Whatcom County. Designed by Bundle Design Studio and built to passive house standards, it demonstrates what's achievable when building science and high-end custom construction are treated as the same project — not competing priorities.

The exterior makes no compromises. All-black standing-seam metal cladding, a warm wood entry canopy, and Vetta triple-pane tilt-and-turn windows create a home that reads as intentionally designed from the street. Inside, polished concrete floors, wide-plank white oak, cherry cabinetry, and terrazzo tile reflect the same standard of craft — the kind of finishes Bellingham homeowners typically have to leave the county to find.

The building envelope is where this DADU earns its performance numbers. 3.5 inches of mineral wool continuous insulation, a fiberglass z-girt rainscreen, and Blueskin VP100 air barrier — with every single penetration taped and sealed — produce an ACH50 of 0.4. For context, standard new construction in Washington State lands around 3–5 ACH50. The result is a home that stays quiet, comfortable, and cheap to heat and cool year-round.