"City planning rules" meaning… zoning? It's entirely out of date, and next to nothing would be built here without minor variances or zoning amendments, simply as it would not be economically supportable: no-one can pay what's wanted for the land without dividing its cost across many units now.
Despite our outdated zoning, increased density is desirable for many reasons including planning ones. With more density we can bring down the cost of City services (and therefore your taxes) by making the delivery of the services more efficient. From an ecological POV, it's a huge boon to have more people in less space as it preserves farmland around the city, it preserves the watersheds around the city, it cuts down on the pollution emitted by vehicles that would be crawling along suburban and exurban arterials to take people to their distant cookie cutter tact subdivisions, it cuts down on the toll of stress those commutes exact, etc. etc. Density is good.
In the meantime, in what we call "stable neighbourhoods", density drops over time, as the kids from the young family that moved in years ago move away, and a good number of their parents stay in the homes and empty-nest. That's why schools empty out of course, and suddenly services are no longer so efficient to provide. To maintain healthy population numbers in such areas, we have to have reinvestment in the building stock, and for the past while that's meant towers near transit stations and avenues type buildings along the arterials. It's not enough though, so steps are just starting to be taken that will allow gentle density increases on neighbourhood streets. To save everything around the city that's worth saving as per the previous paragraph, we have to face the density increases, and we do need better ways to deal with it, both during construction (fewer lane closures) and afterwards (better transit to take the pressure of roads, more walkable shopping opportunities, etc.). It's those kind of investments that come with or follow density increases that we will need to stop such places—whole neighbourhoods—from declining into tenement-like states, or raising them out of them.
So, yes, new buildings come with some pain attached, but if they are well planned then the result should be a better neighbourhood and a better city as a while at the end of it.
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