Boston architecture studio Studio 3.0 has added a wedge-shaped extension and a screened-in porch to an octagon-shaped house in Cape Cod originally built in the 1970s, keeping the addition distinct from the original core.

Located in Truro, Massachusetts, the Octagon: Revisited project followed the owner’s desire for more space for a growing family while retaining the original structure of a house built in 1974.

Studio 3.0 has added a wedge-shaped addition to a 1970s octagon house in Cape Cod

“Importantly, the Octagon itself has enormous sentimentality for the family, so it was imperative that it stay intact and that the addition – a new bedroom, bathroom, and office space – be a truly independent extension of the existing home,” said Studio 3.0 principal Josh Slater.

The project encompasses two extensions – both of which branch off opposite sides of the house – and updates and reconfiguration of the original 780-square-foot (72-square-metre) octagon core.

An extension and screened-in porch branches off opposite sides of the original structure

Its design centres around the client’s desire to keep the addition noticeably distinct from the original house while playing off its structure, which was difficult to add directly on to, according to Slater.

“Lifted into the tree canopy by a minimal concrete foundation, the entire structure is essentially eight wood trusses that hang off a single 6″ (15 centimetres) HSS metal post in the centre,” he said.

Yellow was used to highlight exterior structural elements

The solution was to create two cantilevered “wedges” that jut outwards from the octagon’s perimeter and are supported by metal columns. One contains an enclosed residential space and the other is a smaller, screened-in porch.

The porch aspect juts directly from the face of the octagonal house, while the residential extension was rotated 22 degrees to “assert itself as a distinct volume”.

Another rectangular volume was sandwiched between the house and the residential extension. This volume holds a new staircase for the house, which doubles as a gallery for the owner’s art.

“The stair tower between is a simple vertical volume to further separate – figuratively and literally – the new from the existing,” said Slater.

On the volume’s interior, the designer left a slice of the original column exposed.

The original interior was reconfigured as part of the project

“I very intentionally set the location of the stair, and that side of the stair wall, just an inch back from that column face. I wanted to express that as its own piece of ‘art’ within the stair volume, and as another nod to the connection to the existing home,” said Slater.

The enclosed addition holds a new bedroom, office and bathroom, while the original structure holds one bedroom, two bathrooms, a kitchen and a living area.

An original column was left exposed in a new stairwell

To reflect the vernacular architecture of Cape Cod, the entire house was clad in accoya wood, a “more sustainably sourced” version of the common weathered cedar siding found in the area, with vertical siding used on the original house and horizontal on the extension.

Additionally, some elements on the exterior were marked with a “playful and joyful” yellow. Slater noted the colour was chosen during the 2020 pandemic when the team wanted something to make them smile.

The addition contains a new bedroom, office and bathroom

“The ‘question’, so to speak, in my mind was how do you engage with such a distinctive existing condition, rather than avoiding addressing it – but it was critical to do something that is responsive without being too literal,” said Slater.

“The addition should be in dialogue with the existing building.”

Elsewhere in Cape Cod, a campaign was launched to save Marcel Breuer’s holiday home from demolition, while Dezeen recently rounded up the top 10 house extensions of 2024.

The photography is by Gregg Shupe

Project credits:

General contractor: Lemanski Construction
Structural engineer: Siegel Structural Engineers

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