Where Could Two Duplexes Be A Good Redevelopment Strategy?
- Jul 26
- 9 min read
Updated: Jul 29
Updated July 28, 2026 to include summaries; scroll down to Results
Two duplexes on a single lot could be a way to achieve the reasonable profit on redeveloping a single-family lot, that everyone got into their heads when the SSMUH legislation was introduced. I'll show you how to take advantage of the SSMUH rules and to take advantage of everyone's familiarity with the duplex typology. More importantly, I'm going to point you toward the cities and lot types on which this concept is mostly likely to be viable.
Fourplexes are alien to lenders, insurers, builders, and buyers who subsequently are hesitant to become involved with them. Nonetheless, building and selling four dwelling units may be the only way to make a positive return on investment for an average residential lot.
If you have considered building a fourplex because you understand the basic underlying math in which development charges and similar fees can be covered often only if you can sell four units, you've probably encountered the perceived complexity of a single, four-dwelling building and abandoned the idea. This double-building format may be the redeeming variant.
David Babakaiff of VanPlex has written a number of insightful posts on multiplexes, and there are three recent ones in particular that I found helpful as a reference: this one about specialists (link), this one about the motivation for developing a multiplex (link), and this one about when the math for multiplexes doesn't pencil out (link).
The Economics Have Shifted Toward Stratified Development
Large, multifamily, rental buildings have been recently completed or are nearing completion. The gradual increase in supply has not been enough to make renting easy, but it has brought rents down. Development costs have risen significantly and construction costs have continued to escalate, aggravated by the Hormuz blockades and tariffs. Interest rates have been brought up to a normal level, so the revenue from a rental building is typically not enough to recoup the total cost of development. A big part of the calculus therefore is the anticipated resale value of stratified condo units.
Very rough math here, assuming you own the land and have little or no mortgage, and the permitted FSR is 1.00. This does not mean that owning the lot makes the land free. However, an owner who acquired the property years ago may have considerably more flexibility than a developer purchasing it at today’s price. Assume $1.4M for hard construction costs at $350 / ft2 and $1.5M for soft costs and development charges. Building four units each around 1000 square feet and selling them for $950k each, the building will yield around $1M of profit. The margin increases if you can build at more than FSR 1; it decreases if the FSR is lower. These are very broad stroke numbers, but it shows that there can be potential.
Why a Fourplex Is Efficient - And Often Impractical
A single building containing four dwelling units - a fourplex - is the most efficient building form from a technical sense. Less heat loss in winter, less exterior wall to build, and there is only one service connection for each of the utilities.
A fourplex is a different beast than a side-by-side duplex though. It's almost an apartment building and has additional fire protection requirements and other construction differences. On a traditional sized lot an an efficient form, the number and size of windows to provide enough light to the interior, are not possible.
Dividing the four units into two duplexes can produce more usable homes, but the penalty is more exterior wall and roof area and some duplicated building systems.
Stacked Units Can Reduce Construction Cost
Most contemporary duplexes place their dwelling units side by side. One benefit is the simpler fire separation wall compared to a fire-rated horizontal floor assembly.
The drawback is width: on a 33-foot lot, setbacks and exterior-wall thickness can leave each dwelling less than 12 feet wide internally. These units always feel narrow. A 45-foot lot produces substantially more usable side-by-side dwellings, but the wider land is much more expensive.
Stacking one dwelling above the other can produce a more efficient floor layout and reduces construction cost. Structural loads run directly from the roof straight down to the foundations, which reduces the need for costly beams and other expensive structural elements. Kitchens and bathrooms can also be aligned vertically, resulting in less expensive and more reliable piping installation.
Depending on the design, these efficiencies may reduce the total project cost by several percentage points. On a four-unit development, that difference could amount to approximately $100,000 to $200,000. The actual savings would need to be tested against the additional fire, acoustic and access requirements associated with a vertically stacked configuration.
Repeating the Duplex Creates Economy of Scale
Building a second, substantially identical duplex on the same lot creates another form of economy. Twice as much construction is completed, but the builder does not need to resolve twice as many details. The second building uses the same dimensions, assemblies, materials and construction sequence as the first.
The reduction in labour may not be obvious because the two buildings would initially proceed almost in parallel. Nevertheless, repetition reduces layout time, construction errors and the number of one-off decisions made in the field. Trades can also repeat work they have just completed rather than interpreting a different set of conditions.
Lot Geometry Determines Whether Two Duplexes Will Fit
The permitted floor area alone does not establish whether the development will work though. Site coverage limits, setbacks, building separation, parking, and replacement-tree requirements all compete for the same limited ground area.
If parking is required on the site, two duplexes might be separated by only the minimum building-separation requirement to satisfy the building code and the zoning bylaw, but it does not create useful outdoor space. It produces a passage between buildings, not a yard.
The Rear Building Rules Are Critical
In the Lower Mainland zoning bylaws reviewed to date, a rear principal building is generally limited to two storeys. Many municipalities also prohibit a roof deck on the rear building to control overlook into neighbouring yards.
A two-storey rear building is sufficient for a duplex, but only if each principal building may contain at least two dwelling units. Some bylaws permit four units on a lot while restricting how those units may be distributed. Permission to build four dwellings does not necessarily mean permission to build two duplexes.
The proposed development therefore requires all of the following:
The lot must qualify for at least four dwelling units.
More than one principal building must be permitted.
The rear principal building must be allowed to reach at least two storeys.
Each principal building must be permitted to contain at least two dwelling units.
Parking must either be waived or accommodated without making the buildings and outdoor spaces impractical.
Required replacement trees must be capable of fitting around the buildings, parking and access routes.
Minimum Lot Area Is One Of Many Filters
The first requirement is permission to build four dwelling units. Under the SSMUH provisions, this generally requires a minimum lot area of 280 square metres, or approximately 3,014 square feet. That threshold says little about whether two duplexes can actually be constructed. A qualifying lot may still be too narrow, too shallow or too constrained by trees, servicing, and parking requirements.
(RED Select)
The next filter is whether the zoning bylaw permits more than one "principal building" on a single lot. Based on the municipal provisions reviewed to date, multiple principal buildings appear to be permitted in:
Vancouver
Burnaby
Coquitlam
Port Moody
Richmond
Abbotsford
The following municipalities do not appear to permit two full-sized principal residential buildings, though a coach house or accessory dwelling unit is permitted:
Port Coquitlam
Surrey
City of North Vancouver, where permission appears unlikely
District of West Vancouver
The position remains to be confirmed for:
District of North Vancouver, where permission also appears unlikely
Maple Ridge
Municipal terminology is inconsistent, and some bylaws distinguish between a principal building, an accessory dwelling or coach house, a detached suite and other forms that may contain dwelling units without qualifying as a second full-sized principal building.
Some municipalities have historically used different names for two-unit buildings depending on how the dwellings are arranged. In Vancouver, for example, “duplex” once referred to two dwellings stacked one above the other, while side-by-side dwellings were classified as “semi-detached.” That distinction appears to have largely disappeared, but for redevelopment purposes, the name matters less than what the bylaw permits: whether they may be stratified and whether two such buildings may occupy the same lot.
Results
I've tabulated some scenarios for different lot sizes in some of the cities that permit two duplexes. These observations assume identical front and rear duplexes, both 2 storeys tall, with a target unit size of 1200 sq.ft. and a reasonable courtyard between the front and rear buildings. These are crude numbers and don't take into account site specific factors. Their intent is for general comparison only.
Vancouver
Vancouver's development cap is primarily the maximum floor space because there's no limit on site coverage. Paying the community amenity contribution fee to increase the FSR from 0.70 to 1.00 is the only way to achieve reasonable sized dwelling units of at least 1000 sq.ft..
For a 33'x122' lot, the courtyard would be about 20' deep; for 45' wide lot the courtyard is 27' deep. Parking isn't required anywhere in R1-1, but it may make selling the units easier. The penalty is losing the generous courtyard which becomes the minimum 8' wide separation.
Summary: two duplexes work reasonably even on a 33' wide lot if you can sell without parking; otherwise choose another format such as a 3-storey front building and parking tucked into the 2-storey rear building. A 40' wide lot with parking could yield 1200 sq.ft. units but with minimal courtyard.
Burnaby
In contrast to Vancouver, Burnaby's limitation is primarily site coverage since it has no cap on the floor space ratio.
Summary: twin duplexes don't take the best advantage of the zoning bylaw. The site coverage limitation caps the floor plate before either the absence of a lane or parking even make much of a difference. A 33'x122' lot is too small for twin duplexes. A 49'-6" wide lot could give 1200 sq.ft. units with a 30' deep courtyard even with parking
Coquitlam
The minimum lot width in Coquitlam is 12.5m (~41') for R-2 and 18.5m (~60') for R-1. R-3 doesn't permit two duplexes. The maximum FSR/FAR for R-1 and R-2 is 0.75, but the parking requirement is comparatively high. There are no frequent bus routes, so parking is required everywhere except where close enough to a Skytrain station that taller buildings are permitted and more feasible. 6 parking spaces required for the four units need to be incorporated, so a unit with a rear lane is preferable by far. We see 1500 sq.ft. units only with a 66' wide lot, and the courtyard could be about 30' deep.
Summary: Coquitlam lots seem to fair better with fewer units, such as a single duplex perhaps with a coach house.
Port Moody
As with Burnaby, the main limitation for this typology is the site coverage; the floor space limit is 0.8. The presence of a lane doesn't impact this stacked building type's maximum size. Even outside 400m of a frequent transit route and requiring parking, the courtyard could be 20' deep on a 33'x132' deep lot.
The challenge in Port Moody is that most of the lots are on sloped sites, so access and developable area are unpredictable.
Summary: The lots are usually larger and the parking requirement fairly low, but the slopes in this city are not inherently conducive to this simplistic typology.
Richmond
Observations coming soon
Abbotsford
Observations coming soon
What Does This All Mean?
I have spent much of the past 15 years designing multifamily buildings and the past three following British Columbia’s evolving SSMUH rules. I believe in their basic promise: creating more homes without squeezing everyone into shoebox condominiums.
I like buildings in which every decision earns its keep. Straightforward forms and efficient planning can lower construction costs while producing buildings that are easier to build and more reliable over time. The technical and aesthetic sides of design should support one another.
My double-duplex designs follow that approach without defaulting to generic boxes (like those which infuriated everyone in Burnaby enough to tweak the zoning bylaw). Economical forms, careful proportions, and restrained detailing allow them to fit their neighbourhoods rather than simply occupy them.
For owners who have watched the promise of four units lose its financial lustre, the choice is becoming blunt. Do you build two duplexes and sell them, or keep an ageing house while stagnant rent and rising expenses erode its cash flow? Waiting may feel cautious, but the arithmetic may disagree.
The Litmus Test
Determining whether or not specifically two duplex buildings can be built requires a formal study - not just a quick FSR calculation. My RED Report was created to identify all the development options available. For someone who is already looking at a couple specific options more closely, I offer the RED Select to explain the main site constraints and illustrate the viability of a few development configurations.
To download a sample RED Select, click on the image below.
If you'd like to book a free, 30-minute consultation with me to discuss how to move your development plans from the rough idea stage into the solid research phase, click the button below.
DISCLAIMER:
The information included in this article is to an extent generic and intended for educational and informational purposes only; it does not constitute legal or professional advice. Thorough efforts are made to ensure the accuracy of the article at the time of writing, but having read this article, you understand and agree that Daniel Clarke Architect Inc. disclaims any legal liability for actions that may arise from reliance on the information provided in this article. I am an architect in BC, but readers are recommended to consult with their own architect on their specific situations before making any decisions or exercising judgement based on information in the article.
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