Multi-Family & Multiplex Permit Design
Permit design for converting or developing qualifying low-rise residential buildings with multiple dwelling units. We start with zoning and the existing building because unit count, exits, fire/life-safety and servicing can change the entire design approach.
What a multiplex permit package can include
Depending on the building and agreed scope, 828 Design can prepare:
- existing and proposed floor plans showing dwelling-unit layouts and common areas
- site plan and zoning information
- building sections, elevations and construction details
- exit, stair and fire/life-safety information
- coordinated plumbing, HVAC/mechanical and Building Code-related electrical/lighting information within applicable scope
- building-structural permit information within applicable qualification and coordination of independent professional input where required
The issues we review before locking in unit layouts
A successful multiplex conversion is a coordination exercise, not only a space-planning exercise.
- how many units the municipality currently permits on the property
- existing building classification, permit history and legal unit count
- exit paths, stairs, fire separations and life-safety systems
- bedroom/window and room-layout constraints
- plumbing, drainage, HVAC/mechanical and utility implications
- structural changes, additions or exterior alterations required to create the units
Unit permissions are municipality-specific
Do not assume that a unit count permitted in one Ontario municipality is automatically permitted in another. Toronto currently has a building-permit stream for conversions to duplexes through sixplexes, while its zoning permissions continue to evolve by area and building type. For every project, we verify the current local zoning and applicable-law path before relying on a proposed unit count.
Common multiplex conversion questions
Can I convert any house into a fourplex?
No. The property must first support the proposed unit count under current municipal zoning and planning rules, and the building must be capable of meeting the applicable Building Code requirements.
Can the existing basement count as one of the units?
Potentially, but it must be reviewed as part of the overall building. Basement conditions, exits, ceiling height, fire/life-safety, plumbing and HVAC can affect whether the proposed unit is workable.
Do all units need separate entrances?
Not necessarily separate exterior doors, but the building needs compliant exit arrangements for the proposed configuration.
Will a multiplex conversion need plumbing and HVAC drawings?
Often some level of plumbing, drainage and HVAC/mechanical coordination is required because the number and arrangement of dwelling units changes the building services.
What if the house already contains several units but the city records show fewer?
That is an existing-condition/legalization issue. Permit history and actual construction should be reviewed before assuming the current unit count is recognized.
Can 828 Design handle the entire permit package?
828 Design can coordinate the building-design and permit-documentation scope within applicable BCIN qualifications and can coordinate separate regulated professionals where required and included.
After permit issuance
Multiplex construction must follow the approved unit layouts, separations, exits and building-service information. Material changes made during construction can affect multiple Code systems at once, so proposed changes should be reviewed before they are built.
What to send for a quote
- property address and municipality
- current and proposed number of dwelling units
- existing floor plans or a sketch of the current layout
- photos of stairs, exits, basement and mechanical/service areas
- survey and prior permit records if available
- any municipal zoning review, order, inspection note or existing unit documentation
Related residential permit services
Basement Apartment Permit Design · Zoning Feasibility Review · Interior Alteration · Plumbing Permit Drawings · HVAC & Mechanical Permit Drawings
828 Design Inc. — BCIN building design & permit services. Content reviewed for current Ontario permit context: August 2026. Requirements are confirmed for the property, municipality and agreed project scope. Qualifications & responsibility →
Considering a duplex, triplex, fourplex or larger multiplex?
Send the address, existing layout and target unit count. We can start with the zoning and building conditions that determine whether the concept is realistic.