The Stacked Townhouse

The stacked townhouse — known in Britain as the maisonette, in Montreal as the triplex — resolves this by giving each unit its own exterior entrance while arranging units vertically. The lower unit enters at grade; the upper unit enters via an exterior stair to a door at the second level. Each household has a front door that opens to the sky, not to a shared hallway. The building reads as a single house from the street but contains two or three complete dwellings.

This form has deep roots in cold-climate cities. Montreal's characteristic triplex — three flats stacked, each with its own exterior iron stair — has housed working families since the 1850s. The form emerged not from design theory but from property economics: a single lot, a single foundation, three separate households, no shared corridor to heat or maintain. Vancouver's laneway house policy, adopted in 2009, extended this logic: by 2019, the city had permitted over 4,000 laneway houses, many of them stacked or semi-stacked configurations on lots that had previously held one detached home. The result was density without towers — and without the loss of private ground-level space that towers impose.

Alexander, in *A Pattern Language*, identified the problem but not this solution. His pattern 116, *Cascade of Roofs*, addresses the visual complexity needed when units stack, and his pattern 117, *Sheltering Roof*, insists that each unit feel covered and protected. But he did not describe the stacked townhouse as a distinct type. The critical insight — that you can give an upper-floor dwelling the psychological qualities of a ground-floor home by giving it its own exterior entrance — appears in his discussion of *Main Entrance* (110) but is never synthesized into a building form. The stacked townhouse is that synthesis: cascade of roofs plus individual entrance plus four-story maximum equals ground-related housing at missing-middle density.

The form works because the exterior stair does double duty. It is the thermal airlock (see The Entrance Sequence, 35) — a covered landing where boots come off and coats hang. It is the threshold that separates street from home. And it is the address: a door with a number, visible from the sidewalk, that belongs to one household alone. When the stair is generous — at least 1.2 meters wide, with a landing deep enough for a chair — it becomes a porch, a place to sit on summer evenings and watch the street below.

The upper unit in a stacked townhouse can still have private outdoor space: a generous balcony, a rooftop deck, or a rear yard accessible by an internal stair. The lower unit gains the full depth of the garden. In Montreal, the classic configuration gives the ground-floor unit a rear yard while the upper units share a flat roof that doubles as a terrace — each household with its own outdoor room.