Secondary suite and ADU are two different ways to add another home
In British Columbia, an in-home secondary suite and a detached accessory dwelling unit (ADU) can both add a self-contained home to a property, but they create different zoning, design, servicing and construction questions. A secondary suite is part of the principal residential building. An ADU is a separate accessory building or a self-contained unit in a detached accessory structure, often described locally as a garden suite, laneway home, coach house or carriage house.
The provincial small-scale multi-unit housing framework generally requires local governments to enable at least one additional housing unit in qualifying restricted zones, but local implementation determines whether the property can use a secondary suite, an ADU, either form, or both. The exact lot still has to satisfy the municipality’s zoning and permit requirements.
What is a secondary suite in BC?
A secondary suite is a self-contained dwelling unit located within a residential building or a qualifying portion of one. It has its own living, sleeping, cooking and bathroom facilities. The BC Building Code contains specific requirements for secondary suites, including life-safety and construction provisions.
Typical examples include a basement suite or a suite at grade within a detached house. Depending on the building configuration and the current Code, a secondary suite can also be possible in certain vertically separated residential forms. Local land-use bylaws still decide whether the use is permitted on the property.
What is a detached ADU?
A detached accessory dwelling unit is a separate residential unit on the same parcel as the principal home. Municipalities use different names: garden suite, laneway house, coach house, carriage house, backyard suite or detached ADU. Because it is a separate structure, the planning review usually pays closer attention to setbacks, height, lot coverage, access, privacy, servicing and the location of other buildings on the lot.
An ADU can be attractive where the main house is difficult to retrofit or where a homeowner wants more physical separation between households. It can also be more complex and expensive because it is effectively another small building rather than an interior renovation.
Secondary suite vs ADU: the practical differences
| Question | Secondary suite | Detached ADU |
|---|---|---|
| Location | Inside the principal residential building | Separate accessory building on the same lot |
| Typical local names | Basement suite, secondary suite | Garden suite, laneway home, coach/carriage house |
| Main zoning focus | Use permission, unit count, parking and building form | Use permission plus setbacks, height, lot coverage, access and siting |
| Construction scope | Alteration/addition within an existing building | New detached residential construction or conversion of an accessory building |
| Servicing | Often tied into existing building systems, subject to capacity and code | Often requires a more explicit servicing design for water, sewer, electrical and drainage |
| Privacy | Households share one building | Greater physical separation is possible |
Which option does provincial law require municipalities to allow?
The current provincial SSMUH policy manual explains that, for lots where the higher three-to-six-unit rules do not apply, local governments may implement the one-additional-unit requirement in several ways. They can allow a secondary suite, allow an ADU, allow the owner to choose either form, or allow both. That means the phrase “BC allows an ADU everywhere” is too broad.
The correct next step is to check the municipality’s zoning. Some communities broadly enable both forms; others attach different lot, zone, servicing or design conditions to detached units.
Servicing can decide the project
Water and sewer capacity can change which option is practical. The provincial policy manual specifically distinguishes properties that are not served by local-government sewer systems, and local requirements can also deal with utility connections, drainage and fire access. A detached ADU commonly needs a clearer site-servicing plan because the new unit sits away from the main house.
For an in-home suite, the existing plumbing, electrical service, heating and ventilation systems still have to be assessed for the additional dwelling. The Province’s homeowner guidance recommends confirming utility capacity and Code requirements early rather than after plans are finished.
Building Code checks for a secondary suite
BC’s homeowner guidance highlights topics such as ceiling heights, safe exits, bedroom windows, fire separations, smoke and carbon-monoxide alarms, heating and ventilation, electrical capacity, plumbing and radon measures. The exact requirements depend on the project and the applicable Code provisions.
Do not use zoning approval as proof that the building is ready for a suite. A property can have land-use permission and still require substantial construction work before the suite can be legally occupied.
Site-planning checks for a detached ADU
For a detached unit, start with a site plan. Measure the lot, existing house, accessory buildings, setbacks, parking/access areas and available servicing routes. Check tree protection, heritage, hazard, agricultural-land and easement constraints where relevant. These issues can determine whether the theoretical zoning permission produces a buildable location.
The garden suite, laneway home and ADU guide explains these detached-unit questions in more detail.
What about lots covered by the 3 / 4 / 6-unit rules?
If the property is in the higher-density SSMUH framework, the choice is not limited to “one suite or one ADU.” The local zoning may have to accommodate three, four or six dwelling units depending on the parcel and location. Read the BC 3 / 4 / 6-unit rules guide and use the BC unit-count tool before assuming the one-additional-unit branch controls the property.
How to choose between a suite and an ADU
Choose the in-home suite path first when the existing house has suitable space, acceptable ceiling heights and exits, and the renovation can be completed without disproportionate structural work.
Explore a detached ADU first when the lot has usable rear-yard or side-yard space, the municipality clearly permits the form, and the project benefits from a separate building. The detached option can also make sense when privacy and long-term flexibility matter more than minimizing initial construction cost.
Do not choose based only on the provincial headline. The best option is the one that survives all four checks: zoning, site fit, servicing and Building Code/permit feasibility.
Official BC sources
Sources reviewed September 27, 2026. Building Code and municipal zoning requirements can change; verify the current authority before design or construction.
Check your municipality
Local implementation is the deciding layer. Start with Vancouver, Surrey, Burnaby, New Westminster, Richmond, Saanich or another municipality in the BC city directory.