One of the solutions that many local politicians talk about when it comes to increasing the supply of housing without building towers everywhere is infill – unobtrusive additions through laneway houses, suites in existing homes, granny flats over garages, and duplexes and triplexes.

But a new analysis of infill housing in the region shows that many Lower Mainland cities make it difficult for owners and builders to create those new kinds of housing in single-family zones, with long permit times and sometimes huge fees.

And that's a problem, because the region's single-family housing occupies two-thirds of all the land in the Lower Mainland, making it an untapped resource, says Bob de Wit, chief executive officer of the Greater Vancouver Home Builders' Association.

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"This is not the whole solution to the supply problem. For that, you need more condos, more of everything. But it is one solution," said Mr. de Wit, whose association's report was released Monday.

The association, which did the research for the Housing Approvals Study together with the land-records-tracking company Landcor, found that the proportion of infill projects in the region accounted for only 15.5 per cent of all new housing stock in the region in 2016. That had barely increased from 13.5 per cent in 2012.

The processing times varied wildly, from seven months in the City of Langley for an average infill project to 24 months in Langley. Processing fees ranged from $18,000 in Port Coquitlam to $61,000 in the District of North Vancouver.

Many builders end up doing straight one-for-one replacements of single-family houses when they build because of the complications, said the study.

Mr. de Wit said his organization did the research – the third year it has studied an aspect of construction processes in Lower Mainland cities – to demonstrate the difference between cities and spur them to improve their practices.

His association is recommending that all cities adopt a set of best practices in order to speed up housing approvals without sacrificing quality.

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Those best practices include pre-zoning for new kinds of housing (the way Vancouver has approved laneway houses as an outright option for all single-family lots in the city), a special Nexus-type stream for applications from experienced builders and architects, online permitting, and a co-ordinator who acts as a single point of contact for a project.

The association's report notes that many cities still have minimum lot sizes of 50 to 80 feet – far more than the 33-foot standard in denser parts of the region.

Those lots could easily accommodate more duplex or triplex housing, if cities would open the doors to that by modifying their zoning. Recent census data has showed that some of the region's single-family zones are actually losing population because there are fewer people per household compared to 10 or 20 years ago.

The report also makes the case that the region is falling behind in building housing for new people moving in by 4,400 units a year. Its analysis concludes that only Vancouver, Richmond and the City of North Vancouver built more supply than was needed for the anticipated population. Every other municipality fell short of the amount needed for the population projected by Metro Vancouver's Regional Growth Strategy.

Mr. de Wit said that many municipalities have introduced policies to encourage infill housing.

Vancouver, which has 75,000 single-family houses within its boundaries, has been the most successful with that, in part because of its laneway-house policy. Surrey, with 80,000 single-family houses, is second.

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The report ranks municipalities on an overall basis, not just on their infill policies, but also their processing times and fees to assess which are "best poised to implement infill housing policies."

In that ranking, Burnaby comes in first, although it has no specific infill policy for its 27,000 single-family homes. Langley Township and New Westminster are ranked second and third, while Vancouver comes in at number nine and Surrey doesn't make the list of the top 10.