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"Multiplex" covers duplexes, triplexes and fourplexes — the "missing middle" between a single house and an apartment. Provincial reform has widened where these are allowed as-of-right.
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Ontario's Bill 23 permits up to three residential units on most residential lots as-of-right, without a rezoning and without added parking minimums. That makes a triplex — or a house plus two units — achievable on many ordinary Markham lots that previously allowed only one home.
Going to four or more units, or a built form the zone doesn't contemplate, generally still needs a planning approval (a rezoning or variances).
Even within the three-unit allowance, the building has to fit: lot coverage, setbacks, height and storeys, and servicing all constrain the envelope. The form (internal units vs. a new multiplex building) changes what's realistic.
SiteIQ tests your parcel against Markham's standards and ranks development scenarios by fit and return, so you can compare a second unit, a garden suite, and a multiplex on the same lot.
The Province sets a floor that municipalities can't zone below, but local standards, overlays and servicing still shape the outcome. Treat as-of-right as "no rezoning needed", then check the dimensional rules for your lot.
Is a triplex allowed on my Markham lot?
Bill 23 permits up to three units as-of-right on most residential lots in Ontario, Markham included, subject to servicing and the zone's dimensional standards. Whether a triplex physically fits is lot-specific.
Can I build a fourplex in Markham?
Three units are the province-wide as-of-right baseline; a fourth unit or a larger built form typically requires a rezoning or minor variances. Confirm with the City for your address.
Do multiplex units need parking?
Bill 23 removed minimum parking for the additional units within the three-unit allowance. Site access and servicing still apply.
General guidance, not legal or planning advice. Rules turn on your specific lot and can change — confirm with the City of Markham, and use SiteIQ to read your parcel.