The Semi-detached home is ubiquitous in Toronto. This renovation and addition looks at two primary issues:

Project Name: 125 Semi Addition
Studio Name: WORKS OFFICE of Brian O’Brian Architect
Location: Toronto, Canada
Photography: Scott Norsworthy
Project size: 2800 ft2
Completion date: 2017
Building levels: 3

125 Semi Addition by WORKS OFFICE of Brian O'Brian Architect - Sheet1
Bedroom ©Scott Norsworthy

1. The extent to which the house could be both part of its mirror image, and detached to stand on its own
2. Means by which light might be thoughtfully brought down through the core of this narrow house.

In order to separate this semi, two key approaches were taken. A new STC-rated wall was constructed on the interior of the existing three wythe brick party wall. This sacrifices about 8″ of space for a significant increase in acoustic isolation, an oft-cited complaint about this type of building. A third floor has been added, and the second floor extended.

125 Semi Addition by WORKS OFFICE of Brian O'Brian Architect - Sheet2
Bathroom ©Scott Norsworthy

The overlap at the rear facade deliberately blurs the line between the existing house and the new additions. Light is critical in this type of house. The stair from the first to second floors is along the party wall, as is common in this typology. The deviation comes when the stair turns to cross the house as it rises from the second to third floor.

That crossing provides for an opportunity to experience the verticality of the house, with a skylight above, and an opening below, inviting light into the core of the narrow building. The result is the sense that one is never far from the natural environment, despite the urban location, despite the attachment to the neighbour, and despite the narrowness of the property.

125 Semi Addition by WORKS OFFICE of Brian O'Brian Architect - Sheet3
Exterior View ©Scott Norsworthy

The third floor, consisting entirely of the Master Suite, is bathed in light that varies through the course of the day, starting with morning light that slips through a narrow clerestory window above the original ridge of the front gable of the house. A skylight at the centre of the house makes light an integral part of the experience of the entirety of the building.

Finishes are spare, with White Oak and Douglas Fir travelling through the house, and a deep red Marmoleum flooring used in both the Kitchen, and in the front and rear entries.


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