Large openings and earthy materials feature in a guesthouse that architecture studio Bohlin Cywinski Jackson has added to a private residence on a secluded island in the Pacific Northwest.

The guesthouse was built on a 24-acre (9.7-hectare) property on Henry Island – part of the San Juan Islands archipelago, which lies just off the coast of northern Washington. The property has a main residence designed by Pennsylvania-based Bohlin Cywinski Jackson in 2012.

The site is reached by boat, and a winding path leads from a dock through a wooded area and into a sunlit meadow. The main house sits within this meadow, overlooking a shallow bay.

"When new owners purchased the property in 2016, they engaged us to make additions to the site that respected the natural character of the sparsely populated island," the firm said.

The guesthouse was designed to serve as a flexible space that could accommodate extended stays by family and friends. The rectangular building holds a main living area and two bedrooms.

Totalling 1,350 square feet (125 squre meters), the dwelling is sensitively scaled and relates to the "vocabulary and materials of the main home while maintaining a distinct identity".

The building is located uphill from the primary house – close enough to feel connected but far enough away to offer privacy. Built into a gentle slope, the guesthouse partly cantilevers over the site.

"The slope allowed us to anchor one end of the building into the earth and cantilever the other above grade, minimising disturbance to the ground while creating a distinct character for each of the two bedrooms," the architects said.

One bedroom looks out toward the bay, while the other faces the forest and feels more intimate.

The material palette for the guesthouse mimics that of the main residence – Douglas fir, cedar, steel and glass.

"We used these materials to visually link new and existing buildings," the team said.

A cast-in-place concrete ledge marks the entrance of the guesthouse and visually anchors the building to its site. A wall made of weathering steel serves as a privacy screen.

Inside, the living area acts as a "covered porch" that is flanked by the two bedrooms – a concept that draws upon the covered breezeway found in the main house.

"Large sliding glass doors pocket into the walls on two sides, opening the space and immersing visitors in the sights, smells and sounds of the island," the team said.

Finishes and decor are carefully combined to create a relaxing atmosphere and a relation to the landscape. Several pieces of furniture were custom designed for the space by Bohlin Cywinski Jackson.

The architects noted that because of Henry Island's remote location and limited access, many of the building's components were prefabricated and then transported to the site during the construction phase.

Moreover, the project required intensive planning and coordination due to the tide schedules of the shallow bay around the island.

Other projects by Bohlin Cywinski Jackson include a California winery with a "humble yet refined atmosphere" and a hilltop home in rural Wyoming with an exterior made of wood, concrete and glass.

The photography is by Aaron Leitz unless otherwise stated.

Project credits:

Architect: Bohlin Cywinski Jackson
Interior design: Bohlin Cywinski Jackson
General contractor: Hoxie Huggins Construction
Structural engineer: PCS Structural Solutions
Civil engineer: Pacific Surveying and Engineering
Landscape: Allworth Design
Geotechnical engineer: PanGeo
Surveyor: San Juan Surveying
Fire protection: Commercial Fire Protection
Archaeologist: Cascadia Archaeology
Wetlands delineation: Rozewood Environmental Services