Casa del Árbol

Nestled in a forest of towering redwood trees, there lived a family of four in an iconic, mid-century modern residence designed by the notable, Bay Area firm of Campbell & Wong.  The building is sited right at the edge of Mill Creek, with an adjacent two-car garage, all within a five-minute walk of charming downtown Mill Valley.

The residence is a modest 1200 square feet, and the family was rapidly outgrowing the space.  They invited three architects from across the land to propose initial concepts for increasing the capacity of their home, and challenged them to create a space with many uses, without impacting the idyllic setting.  This included not disturbing any of the redwoods so dear to the family, and protecting or transplanting a number of large ferns, or “helechos”, the original namesake of the property. The challenge was great, as this led to a very restricted area to build on the property.

While seated together around the kitchen table, the family talked about their childhood memories of a treehouse, and with much fanfare the land was renamed “Casa del Árbol” and the vision for the design sprung to life.

Upon hearing of the wishes of the family, the elders of the hamlet of Mill Valley noted that in their laws, it was perfectly plausible to have only one covered spot for a vehicle.  All rejoiced, as this allowed the new design to have both ground level elements that more directly connected to the main house, while the rest of the spaces could soar upward with the redwoods.

Around the parking spot on the ground level were clustered spaces for handwork, clothes washing, storage, and most importantly, music making.  An expressive, exterior stair connects the roots into the trees, via a private deck, to an open, light-filled space for working, sleeping, eating, bathing, and children playing.  The open space is punctured by windows to frame views of the surrounding redwoods from every space.  A large 4×8 skylight in the loft allows one to gaze up into the canopy, and a custom, floor to ceiling, single hung window opens the living area up to the front yard, while acting as a guardrail when fully open.  On the exterior, a simple materials palette references the Campbell & Wong residence.  Horizontal 1×3 T&G cedar siding, in both clear and painted finishes, reflect the original siding; black aluminum windows reference the black, vertical sunshades, and the single hung window is inspired by the large plate glass windows of the residence.

As the vision came to life, the family delighted in the new space.  The colors and textures reminded them just enough of their main house; but when they arrived upstairs, they all whooped with delight at how the space connected to the soaring trees.  It was clear that a grand party was required to truly celebrate the new treehouse.  People came from far and wide to rejoice, and the revelry went long into the night.

Design Challenge

The big, overarching challenge of the project was to fit a vast array of program requirements within a very small site footprint.  The list of desires from the clients included:
  • Remodeling of an existing two-car garage
  • Direct access from the main residence at ground level for laundry, storage, and a music studio
  • Flexible second story space with a his/hers office, playroom, kitchen, full bathroom, sleeping space, and outdoor living area
Close research into the zoning guidelines found that one covered parking space was acceptable.  This allowed the ground floor program to work in and around the garage, which created a side volume clad in corrugated corten steel, to play off the main two-story building.  And above this was the perfect place for an entry deck/outdoor living area. All the second story requirements were accommodated through an open plan that had an office nook, flexible space, and a sleeping loft above the full bathroom.

Physical Context

The solution for a modern treehouse was developed for the project as it responded to the surrounding physical context in many ways:
  • Celebrated and protected heritage, redwood trees
  • Captured framed views of the redwood trees both through the variety of windows as well as a large skylight above the sleeping loft
  • Respected the integrity of the original Campbell & Wong mid-century residence by building adjacent to it
  • Created certain material, color, and design connections with the residence, including:
    • Black aluminum windows referencing the black, vertical sunshades
    • The custom, single-hung window inspired by the large, plate glass windows of the residence
    • Tongue and groove cedar siding, in both clear and painted finishes, reflecting the original siding
Colors and materials either matched the main house – black and gray –  or were of a more natural palette – cedar siding, corten steel siding, concrete pavers, ipe guardrails.