Duncan secondary suite and carriage house rules

Can I add a secondary suite or a carriage house?

Duncan, British ColumbiaChecked against official textSources read 2026-11-05

Short answer

Yes. The City of Duncan's zoning allows one attached suite or one detached suite (in an accessory building) per primary dwelling in the Low Density Residential zone, up to 90 m². A building permit is required, and the City offers pre-approved plans with waived plan review and permit fees.

Key facts

Secondary suite allowed	Attached secondary suites are allowed in Low Density Residential (LDR), and in Medium and High Density Residential only in multi-unit rowhouse dwellings. Zoning permits up to four dwelling units on LDR parcels.Zoning Bylaw No. 3166, 2017 (PDF, consolidated to August 24, 2026), section 4.3, s. 4.2.1, 4.8.2, 4.1.1; Small-Scale Multi-Unit Housing (SSMUH), Secondary Suites, and ADUs, SSMUH page · Wording matched the official text retrieved 2026-11-06 Official wording Secondary Suite, Attached An attached secondary suite is only permitted in a multi-unit rowhouse dwelling permit up to four dwelling permit up to 4 dwelling units on parcels zoned Low Density Residential (LDR)
Coach house or garden suite allowed	Allowed as an accessory use in the LDR zone (one detached secondary suite per primary dwelling, in an accessory building on a parcel with a single-unit dwelling).Sources differ: The City's Secondary Suites Regulations PDF says detached suites require a minimum 600 m² lot, but the current zoning bylaw (amended May 2025) states no lot-size minimum for them; the City's web page says detached suites 'may be permitted where parcels meet the minimum lot size'. Check with the City.Zoning Bylaw No. 3166, 2017 (PDF, consolidated to August 24, 2026), section 4.3, s. 4.2.1, definitions · Wording matched the official text retrieved 2026-11-06 Official wording Secondary Suite, Detached means a secondary dwelling unit located in an accessory building on the same parcel as a single-unit dwelling
Limits	LDR: one attached or one detached secondary suite per primary dwelling unit; maximum floor area 90 m². Detached suites must be at least 2.5 m from the main dwelling; an accessory building with a second-storey detached suite may be 7.5 m high. The zoning text sets no owner-occupancy requirement.Sources differ: The older Secondary Suite Regulations PDF gives percentage limits (attached 40%, detached 60% of the house, or 90 m²) that the current zoning text does not repeat. Searched zoning text for 'owner' occupancy: not checked in detail.Zoning Bylaw No. 3166, 2017 (PDF, consolidated to August 24, 2026), section 4.3, s. 4.3.2, 4.3.3, 3.11.2, 4.3.1 · Wording matched the official text retrieved 2026-11-06 Official wording The maximum number of suites is one attached secondary suite or one detached secondary suite per primary dwelling unit The maximum gross floor area of an attached secondary suite or detached suite is 90 m2 Detached secondary suites must be sited at least 2.5 m from a principal 7.5 m for buildings with a detached secondary suite on The maximum gross floor area of an attached secondary suite or detached secondary
Parking	1 off-street space per dwelling unit, so one for the suite as well as one for the main dwelling. A second space may sit behind the first with a shared access.Sources differ: The older Secondary Suite Regulations PDF says one extra space for the suite plus two for the main dwelling; the current zoning bylaw says 1 per dwelling unit, so it is followed.Zoning Bylaw No. 3166, 2017 (PDF, consolidated to August 24, 2026), section 4.3, s. 3.28.1, 3.25.4; Small-Scale Multi-Unit Housing (SSMUH), Secondary Suites, and ADUs, SSMUH page · Wording matched the official text retrieved 2026-11-06 Official wording Residential Use 1 per dwelling unit may be arranged such that one space is located behind the other space One on-site parking stall is required for each dwelling unit.
Permits	A building permit is required (plans meeting the 2024 BC Building Code). Detached suites also need Homeowner Protection Office approval or exemption. Buildings with three or more units need a Development Permit. A $100 secondary suite inspection fee applies. Building permit and plan review fees are waived if you use the City's pre-approved ADU plans unchanged.Small-Scale Multi-Unit Housing (SSMUH), Secondary Suites, and ADUs, SSMUH page; Secondary Suites, Secondary Suites page; Fees and Charges Bylaw No. 3212, 2020 (PDF, consolidated to August 24, 2026), Schedule E · Wording matched the official text retrieved 2026-11-06 Official wording A building permit application to the City is still required All multi-unit residential buildings (defined as a building with three or more dwelling units) will need to be authorized by a Development Permit Building Permits are issued for construction that conforms to the 2024 BC Building Code Freestanding residential buildings require Homeowner Protection Office approval or exemption 7. Secondary Suite Inspection Fee $100.00
Bylaw	Zoning Bylaw No. 3166, 2017 (amended to August 24, 2026), s. 4.3 and definitionsZoning Bylaw No. 3166, 2017 (PDF, consolidated to August 24, 2026), section 4.3, Part 4 LDR · Wording matched the official text retrieved 2026-11-06 Official wording Low Density Residential Zone Secondary Suite, Detached

How it works

The City of Duncan's Zoning Bylaw allows one attached or one detached secondary suite per primary dwelling in the Low Density Residential (LDR) zone. A detached suite is an accessory use in an accessory building on a parcel with a single-unit dwelling. In Medium and High Density Residential zones, attached suites are allowed only in multi-unit rowhouse dwellings. LDR zoning also permits up to four dwelling units on a parcel. Not all housing forms are allowed on all parcels, so check your lot first.

Steps

Confirm your zone with Development Services at 250-746-6126.
Check flood plain status: LDR parcels east of the Trans Canada Highway are in a flood plain with extra requirements.
Decide whether to use the City's pre-approved ADU plans or a custom design.
For a detached suite, get Homeowner Protection Office (BC Housing) approval or an exemption.
Apply for a building permit with plans meeting the 2024 BC Building Code. A driveway access permit is needed for any new access.

Good to know

Maximum suite floor area is 90 m². A detached suite must be at least 2.5 m from the main dwelling, and one on the second storey of an accessory building may be 7.5 m high.
Parking is 1 off-street space per dwelling unit, so one for the suite as well as one for the main dwelling.
The City's older Secondary Suite Regulations PDF says otherwise on some points (a 600 m² minimum lot for detached suites, percentage size limits, more parking). The current zoning bylaw does not repeat these, so confirm with the City.
Buildings with three or more units need a Development Permit.
The City's pages mention an additional utility charge for secondary suites; ask Development Services what applies.
Pre-approved plans waive only the plan review and permit fees; other costs such as the $100 suite inspection still apply.

What you'll need

Building Permit Application with plans meeting the 2024 BC Building Code
Homeowner Protection Office (BC Housing) approval or exemption for a detached suite

Official forms and pages

The same question in other places

North Cowichan · Ladysmith · North Saanich · Lake Cowichan · Sidney · Central Saanich

Secondary suite and carriage house rules in British Columbia, by municipality →

Sources

Small-Scale Multi-Unit Housing (SSMUH), Secondary Suites, and ADUs, City of Duncan (read 2026-11-05)
Secondary Suites, City of Duncan (read 2026-11-05)
Zoning Bylaw No. 3166, 2017 (PDF, consolidated to August 24, 2026), section 4.3 (read 2026-11-05)
Fees and Charges Bylaw No. 3212, 2020 (PDF, consolidated to August 24, 2026) (read 2026-11-05)
Secondary Suite Regulations (PDF), City of Duncan (read 2026-11-05)

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