Located on the edge of the Swan River in Bicton, this addition is to the rear of an existing federation home. Internally, the project seeks to spatially extend the ‘common’ circulation space of the existing federation house, and notionally widen it to form a generous, shared open space to the rear of the block. These old and new circulation spaces are connected via a black lined portal, an ambiguous space that takes inhabitants from the dark, introverted parts of the existing house, to the more open, external focused space of the addition. The walls on either side of the new spaces are thickened with built-in cabinetry that houses the laundry, kitchen, and storage, freeing up the rest of the space for open living as well as providing insulation from East and West sun. Externally, the project is clearly read as a new addition that frames a series of outdoor interstitial spaces between it and the old house, boundary fences and garden. Constructed from SIPS, the addition is a prototype for a relatively low cost and sustainable type of contemporary home addition.