The City of Sarnia is already working third dwellings into its planning process.
As part of the Ontario government's plan to rapidly increase the province's housing supply, the More Homes Built Faster Act has been introduced.
If approved, it would override municipal zoning laws in some situations and allow up to three dwellings on each residential lot.
Sarnia's Planning and Development Services Manager, Eric Hyatt, said they're already incorporating three units into planning.
"The province has already, through Bill 108, looked at permitting three units on a [residential] lot and we're actually implementing those components through our official plan and zoning update," said Hyatt. "So, through that scenario, three units would be allowed on a lot where there's an existing dwelling. One within the existing dwelling and one in a detached accessory structure."
Hyatt said secondary units were initially approved in 2017, and the bylaw has since been amended to modify the areas they're permitted.
"In 2020, we actually took it a step further and allowed them to go into areas in the suburban and rural parts of the city, on private services, where there was capacity in those systems."
Hyatt said about 28 have gone through the permit system so far.
"So now, essentially, within single-detached dwellings, semi-detached dwellings, townhouses etc., in basically all of the residential zones in the city, you could now have a secondary dwelling."
Hyatt said currently, properties within floodplain hazard areas are not permitted to have additional units.