Ottawa's planning committee has approved zoning changes that would allow coach houses in backyards, despite hearing from community associations worried the city-wide approach doesn't take into account differences between neighbourhoods.

The Ontario government requires cities to allow for extra dwellings in their official plans as a way to boost the stock of affordable housing.

But until now Ottawa's zoning rules have only allowed apartments within existing homes, not separate residential units on the same property.

City staff said they've conducted extensive consultations over the last year, but community associations in some neighbourhoods such as Champlain Park urged planners to return to the drawing board.

They fear allowing the small homes could lead to mature trees being removed or killed, especially if the units are built on the edges of lots or have basements.

How many tiny houses could Ottawa see?

Despite those concerns, staff said they don't foresee many of the houses popping up in Ottawa yards.

"I don't see this as changing the fabric of Ottawa," said John Smit, who manages policy development and urban design for the city.

Smit said he'd be surprised if the city receives more than a few dozen applications for permits each year because it only hands out about 100 permits for basement apartments, which are far cheaper and easier to build.

That feeling was echoed by Murray Chown, who spoke to the planning committee on behalf of the Greater Ottawa Home Builders' Association.

"Certainly none of my clients — small infill builders — have indicated to me that they're just waiting with bated breath for this to work its way through council so they can rush in and file building permits for coach houses," said Chown.

There are many wrinkles, such as attaching coach houses to the main home's water and sewer system, said Chown.

City council will consider the coach house rules at its meeting on Oct. 26. If they're adopted, the amendment "would not be subject to appeal," according to a staff report. That includes appeal to the Ontario Municipal Board, "except during a comprehensive review" of the city's official plan and zoning provisions.

Staff have also been directed to come back in two years with a review of the policy's implementation.