Start Here | What It Is
What Is Missing Middle Housing?
Missing middle housing is a category of mid-density residential building types that fit between detached single-family houses and mid-rise apartment buildings. The term was coined in 2010 by architect Daniel Parolek of Opticos Design.
Key Takeaways
- ✓"Missing middle" was named in 2010 by Daniel Parolek at Opticos Design.
- ✓The category includes duplex, triplex, fourplex, sixplex, courtyard cluster, and small townhouse rows.
- ✓The "middle" refers to building scale, not necessarily middle-income affordability.
- ✓BC's Bill 44 is one of several legislative attempts to legalize missing middle across formerly single-family land.
The Original Definition
Daniel Parolek introduced the phrase in 2010 while working on housing typology research at Opticos Design. The argument was simple. Between the detached single-family house and the mid-rise apartment, there is a whole range of housing types — duplexes, fourplexes, courtyard apartments, bungalow courts, mansion apartments — that used to be common in pre-1940 North American neighbourhoods. After single-family-only zoning spread in the 1950s and 1960s, these typologies became illegal to build on most residential land. They went missing. The original Opticos definition stays narrow on purpose: building types that are house-scale, ground-oriented, and located on lots that historically held single-family homes.
The category does not normally include mid-rise buildings, large strata townhouse complexes on dedicated multi-family land, or any building over three storeys. The point of the category is the in-between scale.
The Typology List
Duplex
Two units on one lot. Side-by-side or stacked. The smallest missing middle type.
Triplex
Three units. Often a stacked main floor + upper, plus a basement suite, on a single lot.
Fourplex
Four units. Two front + two rear is the BC standard. The dominant Bill 44 typology.
Sixplex
Six units. Single-stair Building Code reform makes this newly viable on small lots.
Townhouse Row
Three to eight ground-oriented units sharing party walls. Sometimes counted, sometimes not.
Courtyard Cluster
Four to twelve small units arranged around a shared landscape. Cottage-court typology.
Each typology has its own page in this hub: see duplex, triplex, fourplex, sixplex, townhouse vs missing middle, and courtyard cluster.
A Short History of How Housing Went Missing
Berkeley, California passes the first single-family-only zoning bylaw in the United States, beginning the typological narrowing that missing middle would later try to reverse.
Most North American suburbs adopt single-family-only zoning. The duplex, triplex, and fourplex stop being legal across most residential land.
Daniel Parolek of Opticos Design coins the term "missing middle housing" to name what zoning had quietly removed from the housing menu.
Minneapolis 2040 plan eliminates single-family-only zoning citywide, the first major US city to do so.
BC passes Bill 44 — the Housing Statutes (Residential Development) Amendment Act, 2023 — requiring municipalities to allow three to six units on most former single-family lots.
BC municipalities adopt SSMUH-compliant bylaws ahead of the legislative deadline. Vancouver introduces the R1-1 multiplex zone with secured-rental bonus.
Why the Name Still Confuses People
The term has done its job — it gave planners, journalists, and politicians a phrase to rally around. It also created three problems that anyone reading the legislation and the news in 2026 will run into:
Problem 1: It is not always about the middle
"Middle" was meant to describe building scale, not income. New small multiplex units in Vancouver and Burnaby rent and sell at the top of the local market, not in the middle of the income distribution. The affordability case is a different argument that depends on supply at scale.
Problem 2: Different cities draw the line differently
BC's Bill 44 covers up to six units. Some US definitions include up to nineteen units in mansion apartments. Toronto's policy framework calls these typologies "low-rise multi-unit housing." There is no universal cut-off.
Problem 3: Townhouses are sometimes counted, sometimes not
A row of four ground-oriented townhouses on a former single-family lot is missing middle by most definitions. A forty-unit townhouse complex on dedicated multi-family land is not. The scale and the lot context decide. More on the distinction here.
Missing Middle in BC: Three Layers To Hold Apart
Layer 1: The Typology
Buildings that fit the Opticos definition — duplex, triplex, fourplex, sixplex, courtyard cluster, small townhouse row.
Layer 2: The Provincial Legislation
Bill 44 — the Housing Statutes (Residential Development) Amendment Act, 2023 — and the related SSMUH provincial policy manual that municipalities had to comply with.
Layer 3: The Municipal Bylaws
Each city wrote its own implementing bylaw. Vancouver's R1-1 zone allows up to eight secured-rental units. Burnaby's bylaw caps most lots at four. The District of North Vancouver refused to adopt initial SSMUH provisions and has been the focus of provincial pressure. See the zoning changes page for the city-by-city detail.
Best For
- ✓ Readers who want a stable definition before reading any specific city policy.
- ✓ Builders who need a typology vocabulary that matches the original Opticos categories.
- ✓ Anyone trying to separate the typology from the legislation in their own writing.
Usually Fails When
- ✕ You expect "missing middle" to imply affordability without policy intervention.
- ✕ You assume the term means the same thing in every Canadian city.
- ✕ You conflate Bill 44 with the typology itself.
What To Verify Before Spending Money
- → Whether your local bylaw uses "missing middle," "SSMUH," "low-rise multi-unit," or another term.
- → Whether townhouse projects on your block are counted as missing middle locally.
- → The Opticos source page if you cite the definition in your own writing.
Frequently Asked Questions
Where did the term "missing middle housing" come from?
Is "missing middle" a building type or a policy?
Are townhouses missing middle?
Why is the term confusing?
Official Sources Referenced
Screen Your Lot for Missing Middle
Enter any BC address to see what Bill 44 SSMUH unit count, lot coverage, and FSR your parcel actually qualifies for.