There is a clear, optimal form factor for a cost-effective, ultra high-performance multiplex (SSMUH). Any deviation from this will cost you more to build, whether your lot is 33' in Vancouver, 45' in Burnaby, 66' in Coquitlam, or anywhere else in BC.
In this article, I will share the key aspects of a multiplex building that have a significant impact on the cost of construction, and I will tell you how those aspects should be designed in order to minimize your fundamental costs. You will see why I design multiplexes the way that I do and understand the basic technical rationale.
Most developers and property owners assume they must choose between two extremes: an expensive, high-performance building or a cheaper, code-minimum structure with poor energy efficiency. But this is a false choice. There is a third option: a well-designed, ultra high-performance multiplex that costs no more than a standard code-compliant building. In reality, a fourth, unintended outcome is also common—an overpriced, poorly performing building—yet no one deliberately aims for that result.
If you've been researching the SSMUH / multiplex development option either as an investment to sell for profit, as a source of rental revenue, or as a multigenerational home for your family, you have - or will soon discover - that construction is EXPENSIVE. The high cost has several causes, but you CAN overcome some of them. This may make the difference between achieving a great outcome and losing out on a wonderful opportunity that Bill 44 brought to many homeowners and small-scale developers.
One Headache - Not Several
Although most municipalities allow multiple buildings to comprise a multiplex - you can find out what your options are if you request a RED Report (link to read more) - ONE building comprised of multiple units is going to be the least expensive, for several reasons.
Single Utility Connection
Every building requires its own electrical connection. If a transformer (PMT or LPT) is needed, a single installation is always more cost-effective than multiple setups.
Each building requires a domestic water connection and a separate hot water heating system. A single water shut-off, water meter, hot water tank, and installation is going to cost less. Each building requires a separate stormwater connection and separate sanitary sewer connection. Doing something once usually is less expensive than doing it twice (or more).
Single Domestic System
Each building requires a separate ventilation system. Relying solely on the range hood and bathroom fans is becoming less viable due to airtightness requirements in the building code, so HRV or ERV systems are used most of the time in some way. Depending on how the system is designed, the HRV/ERV could be a significant cost item.
By consolidating the residential suites into one building, there is more room to place on-site parking stalls. This is typically more of a concern for stratified multiplex buildings for sale.
Reduced Exterior Walls
The heating needed for one building is less than the heating needed for two buildings of the same square footage. Consider two hypothetical floor plans: each one a square 24' x 24' for a total buildable floor area of about 1150 sq.ft.. For each floor level, assuming the walls are 8' high, the exterior wall area is 1536 sq.ft..
Now, compare this to a single 24' x 48' building with the same 1,150 sq. ft. floor area. Here, the exterior wall area is just 1,150 sq. ft.—a 25% reduction. At $50 per sq. ft., that’s a savings of nearly $20,000 in insulation and siding costs alone.
Going back to the two square 24' buildings, the length of excavation for the foundation strip footing under the exterior walls is 192'. For the 24' x 48' single building, the length of excavation for the foundation is 144' - again 25% less and using $50/ft. that's $2500 saved in labour and maybe half a day in time because there's less digging for the trenches, less weep tile, less formwork for the concrete, and potentially less concrete.
Build On The Ground
Constructing a building at ground level requires the least amount of excavation. Depending on your site, this could mean avoiding an expensive sump pump for the sanitary sewage. You may live in an area where the bedrock is close to the ground surface, and digging down any amount requires costly blasting.
Another key advantage of building at grade is effortless wheelchair accessibility—eliminating the need for a costly $100,000 wheelchair lift.
Simple, Sloped Roof
A sloped roof is typically less expensive to build than a flat roof partly because:
a gable roof truss is inherently stronger than a flat roof joist
one does not need roof drains - only inexpensive gutters (with leaf guard screens) and downspouts, and
most roof materials options for a sloped roof are less expensive than flat roof membranes.
Many multiplexes feature complex, intersecting gables and dormers—driving up framing costs without adding real value. While these designs may create a more "interesting" exterior, they don’t enhance durability, efficiency, or interior comfort. In fact, the extra roof valleys tend to collect leaves, twigs, and debris—posing a fire hazard in wildfire-prone areas. You don't see it when you're at work or when you're eating or sleeping, so it's a waste. The additional valleys in the roof also are spots where twigs, leaves, or needles can accumulate and catch fire if wildfire embers are in the air. I love ornate roofs such as in traditional Japanese architecture, but the superfluous dormers here in North America are wasteful decoration.
Ultra High-Performance
Finally, consider municipalities that reward Passive House or Net Zero construction with increased buildable area. In Vancouver, for instance, a 19% floor area exemption allows developers to gain extra square footage—adding value through additional rentable or sellable space.
Summary
In summary, the most economical multiplex form is a single structure, built at grade, with a simple, sloped roof.
That being said, there are always other factors. For example, a single building in Vancouver with three or four dwelling units requires a building envelope professional and therefore a CRP (see this article here or this article here). Maybe building one duplex before building a second one makes more financial sense with respect to loan interest and timing. Perhaps the local residents or Planning department would be greatly opposed to a single, larger building - thereby prolonging your Development Permit application process. The raw cost is not the only factor, but it is a massive part of a project's viability.
I've been a Passive House Certified Designer since 2018, and I've been overseeing the technical design and construction of multifamily buildings for private developers since 2009. I've listened to many developers, construction managers, contractors, architects, engineers, and Passive House consultants and certifiers to learn what works in making a high-performance project fit within your budget.
Rather than drifting through an unstructured and habitual sketching process—one that can waste thousands or even tens of thousands of dollars and weeks of valuable time—my structured SAPPHR Strategy ensures a deliberate and efficient approach. Just as a commercial airline pilot or astronaut relies on a checklist to confirm that every critical detail has been addressed, my process methodically verifies that all restrictions have been accounted for, every necessary question has been answered, and all project objectives have been clearly defined. This level of precision happens well before technical documentation begins and long before shovels hit the ground.
Consider starting the design phase of a project having telescopic x-ray vision: you see at the outset all the things that could have been pitfalls, and you see clearly your objectives as they compare to the property. With this approach, your project moves forward seamlessly, avoiding costly redesigns, delays, and budget overruns—until the day you have the keys in your hand. If you’re planning a multiplex, let’s ensure it’s designed for performance, efficiency, and cost-effectiveness from the start.
You could of course stick with the typical process of starting drawings without a clear picture and list of constraints. Although every architect has some conversation with the client before even signing a contract, the first phase of design - schematic design - is treated as a discovery phase... and you're paying an unknown amount. Various obscure bylaws and technical code analyses are left until close to the permit phase, and you have to pay to make changes that compromise your vision. I know that's how things unfold because IT HAPPENS ALL THE TIME on a range of project types and sizes.
Do you own a R1-1 or equivalent property and want to know what your options are for building a triplex or other multiplex? I offer a simple redevelopment study service called the RED Reportâ„¢. Download a sample by clicking the link 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, 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 base on information in the article.