Many owners want to add one home to a lot while keeping the house they live in. The common ways to do that are a secondary suite inside the house, a carriage house above a detached garage, or a garden cottage in the yard. Coquitlam and Port Coquitlam permit all of these on most house lots, and each city sets its own rules for size, placement and parking.
This chapter of the land and zoning guide reads those rules from the cities' own bylaws and pages, checked on 30 September 2026. It explains what each unit type is, how it counts toward the limit on homes per lot, where it can sit, and the permits and parking it triggers. For the full small-scale framework that these units belong to, start with the small-scale housing chapter.
Three unit types and how the bylaw defines them
Coquitlam's small-scale housing page lists secondary suites, carriage houses or laneway homes, and garden cottages among the housing types the province required cities to enable. The exact definitions are in the Zoning Bylaw.
The Part 22 definitions describe each type. A secondary suite is an accessory dwelling unit contained within a residential building that has only one principal dwelling unit. A carriage house is an accessory dwelling unit located mainly above a detached parking structure. It must be smaller than the main building in size, scale and massing, it needs a separate entrance directly from outside, and all its floor area must be at or above finished grade. A garden cottage is an accessory dwelling unit in a single-storey building that is detached from the principal building and smaller than it.
The general definitions in Parts 1 and 2 tie these together. An accessory dwelling unit is a unit ancillary to the principal home on the lot that has not been subdivided from it under the Land Title Act or the Strata Property Act. It counts as a dwelling unit when the bylaw applies the unit limits in a low-density zone, and it can include a secondary suite, a carriage house or a garden cottage.
The "at or above finished grade" words in the carriage house definition matter on a sloping lot. A carriage house with living space dug into the slope does not meet the definition. Section 522 of Part 5 adds a floor size rule for every home: a dwelling unit must be greater than 29 square metres in gross floor area.
How these units count and who can own them
Coquitlam's page on building small-scale housing says accessory dwelling units are allowed as long as the total number of units on the property, principal and accessory, is four or less in the R-1, R-2 and R-3 zones. It adds that the city will not accept a design that could be converted to more than four units later. R-3 is written as two principal units plus two accessory units, so a suite in each half of a duplex is one way to reach four there.
The city's answers on small-scale housing state that secondary suites and accessory dwelling units cannot be stratified or subdivided in Coquitlam. Principal units in a duplex, triplex or fourplex can be stratified and sold. This decides how a backyard unit can be used: the owner of the lot can live in it or rent it, and it stays on the same title as the main home. The chapter on how new homes are titled explains the ownership forms in detail.
Height and placement in the small-scale zones
Part 10 of the Zoning Bylaw sets the height of accessory buildings. In R-1, R-2 and R-3, an accessory building or structure must not exceed 3.7 metres measured from finished grade, or 4.6 metres where at least 80 per cent of the roof surfaces have a pitch of 4 in 12 or steeper.
The bylaw's definition of a principal building adds a point that changes how some backyard units are treated. In a small-scale residential use, a building that contains only an accessory dwelling unit and no principal unit is itself a principal building, because an accessory dwelling unit is a principal use in these zones. Ask Development Planning which height and setback rules apply to your design before you draw it in detail.
For detached accessory buildings in R-1 placed 1.6 metres or more from a principal building, the setbacks are 5.5 metres from the front lot line, 1.2 metres from the rear lot line with or without a lane, 1.2 metres from an interior side lot line and 3.0 metres from an exterior side lot line. Detached accessory buildings must not be in the front yard. Accessory buildings and detached parking structures must keep 3.0 metres from principal buildings. A detached parking structure in R-1 is limited to walls of 10.3 metres and three spaces, and garage doors facing a street are limited to a combined width of 6.0 metres.
| Rule in R-1 | Figure in the bylaw on 30 September 2026 |
|---|---|
| Accessory building height | 3.7 m, or 4.6 m with a roof pitch of 4 in 12 or steeper on 80% of the roof |
| Gap from a principal building | 3.0 m |
| Front lot line | 5.5 m, and never in the front yard |
| Rear lot line, detached and 1.6 m or more from the house | 1.2 m |
| Interior side lot line | 1.2 m |
| Exterior side lot line | 3.0 m |
| Detached parking structure | Walls up to 10.3 m and no more than 3 spaces |
Lane access and parking
Part 7 of the bylaw sets parking for small-scale residential by the size of each unit. A unit smaller than 79 square metres needs one space, a unit from 79 to 158 square metres needs 1.5 spaces, and a unit over 158 square metres needs two. In the A-3, RS-2 and legacy zones the rule is two spaces per principal dwelling unit and one per accessory dwelling unit.
A lane changes the layout. In R-1 and R-2, parking is not permitted in the front yard, the access driveway or the exterior side setback, with two exceptions for lots without lane access. An unenclosed space for an accessory dwelling unit may be in the front yard, and tandem parking may be in the driveway or front yard. The city's Zoning Bylaw page lists Schedule R, which classifies Neighbourhood Attached Residential streets and lanes, and Coquitlam's building page says the city's standard plans are for lots with current or future lane access under Schedule R.
A carriage house brings its own parking because it sits above a parking structure by definition. A garden cottage does not, so the space it needs must fit elsewhere on the lot.
Suites in legacy zone houses
Some Coquitlam houses are still in a legacy zone such as RS-1. Part 22 sets the suite rules there. Only one secondary suite is permitted in a one-family dwelling. It must be inside the principal building and cannot be in a detached accessory building. It cannot be subdivided under the Land Title Act or the Strata Property Act. Its extra parking space must be on the lot and at least 5.0 metres long. Where the house uses an on-site sewer system, the owner needs written confirmation from the licensing body that the system can serve the suite.
Permits for adding a unit in Coquitlam
Coquitlam's development permits page lists intensive residential development, such as backyard suites, duplexes, triplexes and fourplexes, among its development permit areas. It says single-family dwellings do not require a form and character permit. Ask Development Planning whether your proposal needs one.
The city's guide to adding units says a building permit is needed so the work meets the BC Building Code. It warns that the code sets its own separation distances between buildings, which can be larger than the zoning figures, along with structural and ventilation rules. The guide also asks owners to plan for waste bins, driveway width, outdoor amenity space, parking, utility connections and separate metering, and mail. It recommends an enquiry meeting with the city before design work starts.
Port Coquitlam's rules
Port Coquitlam's accessory dwelling unit page describes a detached unit at the rear of the lot, which it also calls a coach house, laneway home or detached garden suite. The lot must be in the RS1 to RS4 zones and must not contain a duplex or triplex. The unit can be up to 90 square metres, at ground level or above a garage or carport. It may be rented, it cannot contain a secondary suite, and it cannot be strata subdivided.
A coach house there can be two storeys, up to 8.5 metres to the roof peak with a roof slope of 9 in 12 or more, or 7.5 metres with a lower slope. It needs 15 square metres of private outdoor space and one parking space that can be reached without moving another car. It must be sprinklered and meet the BC Building Code. The page sets fire access conditions: a paved path at least 1 metre wide from the unit to the street, a route of no more than 45 metres to road or lane a fire truck can reach, and no more than 90 metres to a hydrant.
Port Coquitlam's secondary suites page says suites are permitted only in the RS-1 to RS-4 zones and need a building permit. It asks owners to check title for easements, rights of way and restrictive covenants before they design.
Before you plan a backyard unit
Start with the zone and the lot survey, then check the height, the 3.0 metre gap, the setbacks and the parking against the space you have. On a lot without a lane, draw the parking first. On a sloping lot, confirm the carriage house floor can sit at or above finished grade. On any lot, look at title for a covenant that limits extra homes, which the due diligence guide explains.
The journal article on carriage houses and garden cottages in Coquitlam compares the two types and how the city classifies them for charges. The charges themselves are in the chapter on development charges. City planning staff decide each application, so confirm the rules for one address with them before you commit to a design.