Can Your Infrastructure Handle the Pressure of Infill?
- 2 days ago
- 6 min read
Updated: 46 minutes ago
When thinking about intensification in older neighbourhoods, a question that might come to mind is: “What about infrastructure capacity? Can the pipes, stormwater, and water supply systems support it?”
It’s true. Most older neighbourhoods weren’t built with today’s housing needs in mind. Add a few more homes, and suddenly the pipes work harder, the showers run longer, and the stormwater has fewer places to soak in. But that’s no reason to treat infill like a threat. With the right approach, it’s entirely possible to fit more homes into great neighbourhoods, without bogging projects down in costly, overbuilt engineering standards.
In this article, we’ll dig into what infill really means for infrastructure, how municipalities can make the most of their existing capacity, and what smart strategies trigger housing development and can help us grow responsibly, without leaving municipalities knee-deep in debt or dealing with engineering legacy issues.
How We Got Here: A Brief Tour Underground
In the late 1800s and early 1900s, Canadian cities began installing combined sewers to fight the spread of cholera and typhoid. These pipes carried both wastewater and rainwater, which worked reasonably well until a heavy downpour. At that point, raw sewage and stormwater often overflowed into rivers and lakes.
Post-1965, separate sewers became standard, but older combined systems still burden cities with massive costs for separation, storage tunnels, and upgrades to pre-WWI mains. Ottawa finished its separation decades ago, Toronto retains approximately 23% combined sewers downtown, and Winnipeg remains largely unseparated.
Additionally, older neighbourhoods were built without much attention to grading or overland flow. This was less of an issue when most lots were landscaped and had fewer hard surfaces. Roads handled runoff to sewers, while surface water freely moved between properties with no thought to on-site retention or basement flooding.
Why Today’s Infill Often Improves Infrastructure
Today, new infill buildings are held to a higher standard than their neighbours. Many older homes, generally those built before 1980, still combine storm and sanitary, and flow into the sanitary system. In contrast, new builds must connect to separate sanitary and storm lines whenever possible. New builds also have to manage all rainwater on-site and direct it to the street, unlike older lots that often shed runoff onto neighbouring properties.
Although infill is often seen as adding pressure to existing systems, the reality is often the opposite. Each new project helps move the neighbourhood toward a more modern and more resilient infrastructure network.
When Good Intentions Create New Problems
Municipal rules for small infill projects grow out of good intentions, but they can unintentionally make new housing much harder to build. Many municipalities now insist that small infill projects meet the high standards set for large developments by:
Storing stormwater on-site for about two hours before releasing it gradually, to prevent surges in downstream pipes.
Meeting high firefighting flow rates well beyond life‑safety needs, largely to reduce potential property damage.
On a typical infill lot, the cost of engineering, specialized approvals, and stormwater storage, and fireflow upgrades can quickly make an otherwise ideal project financially unfeasible. These small-scale stormwater systems depend on homeowners to keep them clear—otherwise they stop working altogether. The neighbour who rarely cleans their eavestroughs is unlikely to maintain an underground stormwater tank.
Fireflow upgrades are expensive and can involve upgrades to municipal water infrastructure, perhaps adding a hydrant in front of the new building, or making upgrades to the building design itself to be less combustible. Existing homes in the neighbourhood generally don’t benefit from this investment, it only serves the one infill property being built, which was already designed to stringent fire standards.
A practical alternative is to pool infrastructure costs across neighbourhoods. Collective funding and planning of neighbourhood-scaled stormwater storage solutions and improved water supply would let one set of upgrades serve many homes. This would cut costs dramatically—from as much as $50,000 per property to under $5,000. Until then, isolated requirements will keep small infill projects unnecessarily expensive and risky, stalling the growth of the gentle density Canada urgently needs.
Learning from Copenhagen’s “Sponge City” Approach
Copenhagen is one of the best-known examples of this thinking in action, as they’ve addressed a stormwater problem on a scale even greater than our infill challenges. After a 2011 flood dumped a month's rain in two hours, costing nearly $2 billion in damages, Copenhagen launched its Cloudburst Management Plan in 2012. It planned 300 flood-mitigation projects, including sunken parks, tree-lined boulevards, vegetation patches, permeable pavements and bike paths, designed to hold and slow floodwater before releasing it back into the ground or harbour.
The results speak for themselves: Copenhagen has avoided citywide overflows in major recent storms, and its residents now enjoy greener neighbourhoods, safer streets, and new public spaces that increase property values.
A residential street in Copenhagen with a rainwater ditch to absorb stormwater. Source: Google Maps (2010).
The Takeaway
Allowing more infill does add some infrastructure pressure, but the increase is small and manageable. In Sudbury, for example, our analysis found that even rapid low‑rise growth would increase total hard surface areas by less than 0.1% per year in targeted areas. Many older neighbourhoods still have untapped capacity and were originally built to handle far more people than they do today.
Too often, uncertainty about infrastructure capacity leads municipalities to impose costly, unnecessary on‑site requirements on small builders. Yet the impacts of infill can be forecasted, modelled, and planned for—allowing growth to be directed strategically, where upgrades have the greatest benefit and infrastructure capacity already exists.
With infill opportunity forecasting, municipalities no longer have to guess where low‑rise growth might happen. Planners can now see exactly which neighbourhoods are most likely to intensify, and see the rate of change, based on real economic and market data. This clarity transforms how planners plan—allowing them to align infrastructure upgrades, measure stormwater capacity, and plan neighbourhood improvements with confidence rather than speculation.
It also puts municipalities firmly in the driver’s seat, shifting their role from reacting to one-off projects to proactively guiding neighbourhood change and investing where it will make the greatest long-term impact.
See Where Growth Will Happen
If you’re interested in a demo of BuildingIN’s infill opportunity forecasting, our team can show how it pinpoints likely redevelopment areas, aligns infrastructure planning with real growth potential, and helps municipalities plan upgrades with confidence and precision.
Contact Rosaline at info@buildingin.ca or call 613-262-5480 to begin the conversation.
Rosaline Hill is a principal architect, planner, and development consultant with over 25 years dedicated to designing homes and communities that work. She founded RJH Architecture + Planning, Walkable Ottawa, Ottawa Cohousing, and BuildingIN, each building on her passion for smarter, more sustainable housing solutions.
With support from her CMHC Housing Supply Challenge winnings, Rosaline launched BuildingIN, an infill consulting practice advancing a data-driven approach that unifies Canada’s fragmented housing market for low-rise, multi-unit infill. Her proven methodology has guided municipalities, large and small, through transformative change. Today, she partners with governments across the country, empowering changemakers to unlock scalable, affordable housing solutions where they are needed most.
Sources
City of Ottawa. Sewer Use Law No. 2025-94. https://ottawa.ca/en/living-ottawa/laws-licences-and-permits/laws/laws-z/sewer-use-law-law-no-2025-94
City of Toronto. “The Sewers on the Street.” In What is Stormwater & Where Does it Go? Managing Rain & Melted Snow. Toronto Water, updated November 16, 2017. Accessed March 24, 2026. https://www.toronto.ca/services-payments/water-environment/managing-rain-melted-snow/what-is-stormwater-where-does-it-go/the-sewers-on-the-street/.
Climate-ADAPT (EEA): "The Economics of Managing Heavy Rains and Stormwater in Copenhagen (2013) – The Cloudburst Management Plan." European Environment Agency. https://climate-adapt.eea.europa.eu/en/metadata/case-studies/the-economics-of-managing-heavy-rains-and-stormwater-in-copenhagen-2013-the-cloudburst-management-plan
Harvard Graduate School of Design. "Copenhagen Cloudburst Plan," 7 Aug. 2025. Illustrations by Lucas Dobbin, Nastassja Lafontant, and Donguk Lee. https://www.gsd.harvard.edu/project/copenhagen-cloudburst-plan/
Keele St. Sewer Extension, 1917. Toronto Harbour Commissioners / Library and Archives Canada / PA-097574.
Toronto Avenue Road Sewer. Toronto (Ont.) Records & Archives Division / Library and Archives Canada / PA-055379.
Urban History Review (1995): "Sewage Disposal in Canadian Cities," Urban History Review, vol. 23, no. 2. https://www.erudit.org/en/journals/uhr/1995-v23-n2-uhr0657/1016632ar.pdf
World Economic Forum (2025): "How 'sponge cities' are fighting floods in a changing climate." https://www.weforum.org/stories/2025/08/flood-climate-change-sponge-cities/
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