Open this photo in gallery:

Not that long ago, “fourplex” was a relatively rare term, popping up mainly in news stories about movie theatres or various disasters befalling people who happened to live in this older form of housing left over from the early 20th century.

But last year, the word appeared in 200 stories in the country’s approximately 40 largest newspapers and many hundreds of times more in radio, TV and social media. The big bump came as politicians at all levels, spurred on by vocal pro-housing groups in many cities, started to push the idea of allowing four homes on every residential lot as one way of grappling with the country’s startlingly awful housing crisis.

Federal Housing Minister Sean Fraser has required allowing fourplexes as a condition of getting millions in federal housing money in many cities. The B.C. government has passed legislation that will require four- to sixplexes to be permitted in any city larger than 5,000.

And Ontario is now having a big politically divided conversation over fourplexes. The Ontario Liberal Party, with enthusiastic support from the Greens, are planning to table legislation to allow them everywhere. Premier Doug Ford has come out against, saying it would be a massive mistake to impose that form everywhere.

But why the frenzy of activity over this particular housing strategy? And, even if it suddenly becomes the zoning norm across Canada, what will it really change about the country’s housing shortage – the presumed cause of outlandish housing prices now being paid in Canada for anything with four walls and a roof?

It’s math, plus politics, say many housing specialists. Fourplexes are a form that can be pitched for the largest swath of available residential land in the country. They’re relatively cheap to build. And they’re not too intrusive.

That means, ideally, large numbers of new homes in a form that is the most likely to be accepted by the public, say many housing specialists.

“The people who are trying to make big changes are going for something that is ambitious but isn’t going to get every residential association up in arms,” says Carolyn Whitzman, a planning professor and housing expert based at the University of Ottawa. Fourplexes are not towers or even small apartment buildings.

In Calgary, where the city has allowed fourplexes for years in a small number of zones and is now looking to make it a permitted use everywhere without any apparent “poison pills” that might actually slow them down, advocates say they understand it is a political bargain.

“If they had proposed six storeys everywhere, there would have been a mass uprising everywhere,” said Katherine Davies, with More Neighbours Calgary, a volunteer group of housing enthusiasts.

The potential seems enormous on paper. The 2021 census showed about 53 per cent of Canada’s 15 million “occupied private dwellings” were single-detached houses.

Ontario Green Party Leader Mike Schreiner tweeted excitedly last month that, in his province, “If only 18 per cent of single family homes were converted to fourplexes we would exceed our provincial housing goals by 500,000 homes.” B.C. is projecting 130,000 in 10 years and Ms. Davies said it’s possible there could be 1,000 a year among Calgary’s 150,000 parcels.

But those in the actual business of building homes, along with housing groups that back this movement, all point out that it’s not going to be as easy as the multiplication tables might make it look.

For one, even cities that allow fourplex construction in their zoning may include provisions that actually keep the take-up low. They can require a lot of parking, a feature that can kill even a concrete tower. They can put in design-limited requirements for setbacks or heights. And, most important, they can limit the amount of square feet that can be built on a lot.

Toronto began allowing fourplexes as of last May. Vancouver has allowed them since last September. In both cities, only about 100 applications have been received.

Some critics in Vancouver say that city’s decision to limit the size to the same number of square feet as the total lot (so about 4,000 square feet for a standard lot), which is the same size that a single-detached house is allowed, has deliberately slowed applications.

Vancouver officials say they kept the overall size low in order to make sure that smaller, more affordable homes are built. Others say it appears that they just didn’t want current residents to see too much change.

“They purposefully wanted to make it a soft uptake,” says Jake FryJake Fry, founder of Smallworks Studios and Laneway Housing, which specializes in laneways, and a strong advocate for alternate forms of smaller housing for decades in Vancouver.

The province’s legislation will allow more square feet per lot in other cities, up to 50 per cent more than Vancouver’s.

A second issue with the utopian dream of a fourplex boom is who is going to finance and construct them.

Again, experienced builders say it’s not likely going to be aging boomers, using their retirement savings, or even multi-generational families pooling resources.

Mr. Fry at Smallworks and Bryn Davidson at Lanefab, another well-known infill-house builder in Vancouver, estimated costs in Vancouver for just construction and fees, not land or financing, at anywhere from $1.5- to $2.5-million. That could be less in various Canadian suburbs, but likely not less than $1-million.

The financial risk is likely too large for the average senior homeowner and the multi-generational families will need several adult children with equity or savings to contribute.

Even for those families, says Mr. Fry and others, banks will need to develop a new kind of financing product to service this new “missing middle” form of development, which is not the single-detached houses or concrete towers that banks have loaned money on for decades.

And, in reality, ramping up large-scale production of fourplexes will likely require the growth of a new, niche type of developer.

That’s who is likely to take on this kind of product, says Janna Levitt, an architect with the Toronto firm LGA Architectural Partners.

Ms. Levitt and her husband are finishing up a fourplex with laneway house in the Annex neighbourhood of Toronto and she remains a firm fan of the new option.

“I think politicians are on to the fourplex as a way to make a dent. A fourplex is a great way to start,” she says. “And so many single-family neighbourhoods are emptying out and ripe for this kind of intensification.”

Ms. Levitt said the number of applications are low in Toronto because of the current high costs of construction and financing. But she believes they will take off once the situation eases, especially the cheaper kind of fourplex that is a conversion of an existing large house rather than a new build.

Toronto hasn’t put a limit on the number of square feet allowed and also lets people build a laneway first and live in that while construction on the fourplex is happening – something Vancouver doesn’t – so that is an advantage.

But, like others, she said it’s not likely existing owners or multi-generational families who will build but a new cohort of small-scale developers. That is who is contacting her firm these days about building.

Finally, one more hurdle for fourplexes – not everyone is a fan and that’s not just Doug Ford. Toronto city councillor Gord Perks said they will never create affordable housing and government efforts should be going into the strategies that really do: putting money into social housing, preventing investors from wreaking havoc in the housing market, and improving incomes.

Ontario economist Mike Moffatt, who has turned into a driver of the Canadian public conversation about housing, agrees they are not the cheapest form of housing around.

But they do provide an option for those in the income band that isn’t eligible for government help and never will be.

“Governments are not going to build housing for 70 to 80 per cent of the population,” he said.

That’s where fourplexes can have an impact, allowing some form of smaller, less expensive housing as infill in central cities “Probably not in the millions for the country as a whole. It would maybe max out at 10,000 a year.”