UBC researcher Joseph Dahmen on why so many homes get torn down, and what should replace them.
Joseph Dahmen, Assistant Professor at UBC's School of Architecture & Landscape Architecture, and Jens von Bergmann, data-scientist and mathematician, set out to discover if they could predict which single-family homes are demolished in Vancouver through an interactive tool in order to re-evaluate how reconstruction is approached in Vancouver, and how it influences our city's heritage, affordability, building sustainability, and housing crisis. We spoke to Dahmen about the tool and the future of the project. What was the goal of the project? What did you learn? "We were trying to predict what buildings get torn down or remain in Vancouver, and to do that we looked at what is called RS zoning, which is what most of the 75,000 single-family homes in Vancouver lie within. What we found was that a significant predictor of what happens to a building when it’s bought or sold has to do with the relative building value, which is simply the ratio of the value of the building versus the overall value of a property. When that ratio drops below about 10 percent, that is to say that the entire value of the building is only 10 percent of the overall value of the entire property, we’re looking at teardown rates of around 25 percent. From an architectural perspective we’re basically predicting that if current rates hold, by 2030—just between now and then—we will destroy and rebuild a quarter of the single-family homes in Vancouver. That’s a huge amount and so with that there are heritage issues, the question of how we value our architectural heritage is raised, as are issues of affordability and sustainability." What drew you to this project? "I think most people in Vancouver are pretty familiar with the cycle of construction and reconstruction in the city. I’ve been here for a little more than five years and just in that time I’ve seen a great deal of the city rebuilt and in most cases those buildings were going up where there were older buildings. You’d be hard pressed to find anyone who has lived in Vancouver for any length of time that hasn’t gone past some of these reconstruction sites and wondered what was influencing these choices. There are things that touch people personally around affordability, sustainability and heritage but we really need is a public dialogue about how to move this city forward because these changes come so fast; in a way they’re out pacing the zoning itself. We want to approach that discussion with adequate information—whether it be the teardown index or other means—because we want to be making these decisions in an informed way and so hopefully we can contribute to that." What went into the project? "Building the tool itself took less than a year, but it builds on Jens’s previous work. So it took a couple of years really when you think about the whole process. We used partly open data from the City of Vancouver and also some B.C. Assessment data that helped to establish that relative building value." What’s the future of the tool? Do you have any recommendations for the City of Vancouver? "If we’ve learned anything through this process, it’s that these questions don’t have simple answers. We’re dealing with issues of affordability and sustainability, density, heritage, which are complex issues that are interrelated and touch a lot of different people in a lot of different ways. I can think of ways that I would like to extend the tool to gain a holistic understanding of sustainability questions around operating impacts versus embodied impacts to understand the real environmental implications of what we’re doing right now in terms of how we’re rebuilding the city. But really we want to foster a broader and better informed discussion as we contend with these issues which unfold very rapidly in Vancouver. Our research suggests the need to revisit RS zoning, which now mandates single-family houses replace single-family houses, to look at some other potential uses that might include ground-oriented multi-unit residential buildings for higher density on a lot. Not necessarily everywhere, but strategically oriented so that we can increase the supply that might affect affordability and we can also build those buildings to a higher standard. And interestingly, if we build these multi-unit buildings on land that is currently completely zoned single-family, what you'd find is that the value of those buildings would go up so we’re closer to what we’d call a healthy building value. It’s hard to maintain a healthy building value with single-family homes because the land value is so high that it virtually guarantees that you have to build a super luxury home to be on the right side of the equation, which puts it out of reach for most people in Vancouver. Multi-unit buildings cost more on the whole but it means that individual units will be closer to what people can afford and the building is more likely to last because it won’t be so low on the value scale that is torn down and replaced. What we’ll need is a whole new range of building types that people can get excited about, which is an opportunity for designers to design a future for Vancouver that can provide the kind of spaces that address these issues."