One of the issues cities across North America are grappling with (at least those that are not yet moving on progressive housing legislation, such as California’s SB 828) is the fact that, with single family home zoning, the only thing a ‘teardown’ can be replaced with is another single family home.

Mathematician, data analyst and notorious census mapper Jens von Bergmann points this out, noting that which is dominating the political landscape in Metro Vancouver these days — that when we look at single family home (SFH) development from an affordability perspective, it doesn’t look good.

And from an emissions perspective too — things look mixed at best for entire swaths of SFH neighbourhoods, all across the region.

If replacement homes are built to current, minimal energy standards, we come out carbon negative. If we build to City of Vancouver 2025 standards, or even ‘passive house’ (often referred to in Europe as passivhaus), we recoup the energy debt accrued during teardown/rebuild within about 30 years. But that only works for the first iteration in the teardown cycle.

Frequent Price Tags contributor Ian Robertson illustrates this with a handy analogy:

It is often quoted unthinkingly that ‘the greenest building is the one that still exists’ … to which the only reasonable response is yes, but perhaps only in the very short term. Just as it is reasonable to replace an old dirty car with a new efficient one, so it is with houses.

Essentially, teardowns have a carbon footprint that cannot be ignored, even if, as von Bergmann concedes, “we ignore affordability concerns, [that] we are the centre of a growing metropolitan area.”

(And we can do this, academically at least, and only until October 20th.)

So yes, we know we have to get better about how we accommodate our growth and allow more density. Let’s park that.

But what to do about the fact that from an emissions perspective, as Robertson and von Bergmann calculate, the payback for a code-minimum house in BC is 164 years, more than five times that of the aforementioned CoV or passive house standards?

In a new paper recently published by von Bergmann, with Joseph Dahmena and Misha Dasc, entitled, “Teardown Index: Impact of property values on carbon dioxide emissions of single family housing in Vancouver“, the de facto standard should be to require passive house building standards for all new single family homes.

And that, considering we currently tear down 1 home for every 5 we build in CoV (1 in 7 in Metro Vancouver), we should begin this practice now.

But according to Robertson:

The press talking about the article immediately took exactly the wrong impression of the article, that it suggests we shouldn’t replace existing SFH with multi-family units, whereas the point intended by the authors was specifically that replacement should be done well (and yes, dense).

Robertson extended the car analogy — that the energy used by a typical BC single family house is almost identical to that of a typical car, so the scale of energy savings can also be similar.

An older house is a Hummer, and a passive house is even better than a Prius. And nobody would say ‘the greenest car is the Hummer that still exists’, and thus should they not necessarily say the same for houses. Replacing Hummer Houses should be a virtue, not a vice.

He goes on to note that Vancouverites tend to venerate pre-1940 houses, “as if they were built only with old growth timber by unfathomably skilled hands, and the sine qua non of houses. The reality is that many were quite simply bought from Sears and have been damaged by illegal/unpermitted renovations and rot over the years, and are very likely to have significant structural and other life-safety issues.”

You can read more of Robertson’s thoughts on this topic on the blog Dynamic Cities Project.

And if you’ve got a head for CO2 emissions payback and statistical analysis of energy modeling for residential buildings, check out the UBC paper by von Bergmann et al; once the free version if locked down by Elsevier, it will still be available for purchase.

But the abstract alone is worth a read, by just about anyone interested in building efficiency and the true costs of new construction.

Or you could just consider the following, again courtesy of Robertson:

Keep what is good, replace what isn’t with that which is much better, and if you’re replacing something good, make sure the replacement is the best you can make it. This shouldn’t be a bitter debate.

Comments

  1. The beauty of passive house is it becomes cost effective to heat with electricity and eliminate fossil fuels from operations altogether. They require so little heating energy that all heat and hot water can be supplied by a single high efficiency heat pump.

    The best gas boiler/furnace efficiency is around 90% and can never exceed 100% whereas the latest electric heat pumps average around 300% efficient.

    In addition, the building science that has evolved around the construction of passive house buildings means they are not prone to the moisture damage that is so common in climates like ours. No reason these building envelopes wouldn’t last many times longer, reducing the embodied energy of replacement. There is some additional embodied energy in their construction though.

    This makes it even more important that we have a mid to long range plan as to what neighbourhoods will see higher density and which will remain single family. There is no point in building to passive house standards if the house is soon to be replaced by row houses or apartments.

  2. Renovation is always better than demolition and new construction in terms of energy conservation. The whole ‘old house’ doesn’t need to be replaced, only the parts that don’t meet code, (higher R-value insulation, vapour barrier, new thermal windows in most cases) and a modern efficient electric heating system with electric hot water. Use the back yard for a new passive energy building and double, triple, even quadruple the density in a single family neighbourhood using this strategy.

    1. There are definitely old houses worth saving. But to say that “renovation is always better than demolition and new construction in terms of energy conservation” is not necessarily true. It depends so much on just how much will actually be saved and in so many cases it’s just not that much. A small addition/renovation may be worthwhile to carry the building along a couple more decades, but it will continue to consume five to ten times the heating energy of a modern energy efficient building.

      With a major upgrade to modern standards foundations will often need replacing and with that the basement framing is no longer worth saving. So much new lumber has to be added to bring it up to current loading and seismic requirements that the original framing becomes a hindrance rather than a benefit.

      Air tightness has been recognized as being as important as insulation and it’s nearly impossible to get an old house up to current standards without stripping it down to its bare bones.

      The wiring and plumbing will need replacing meaning the original finishes will need to be opened up and even fully removed in some places. Cabinetry, fixtures, tiles/carpeting/linoleum will be replaced. Upgrading to rain screen cladding means the original cladding will be removed. To bring an old building up to modern standards is a lot more complicated than a DIY weekender is prepared for. Even professional builders struggle to work around the limitations of the original construction.

      There are beautiful old houses and intact neighbourhoods that we can and should preserve as as part of our history. But they’ll never come close to being as energy efficient as even a Vancouver code-built house with their original finishes intact. So we need to question how many we should save based primarily on their historical merit.

    2. The topic is energy supply and utilization. The topic is not foundation design, seismic design, rain screen or not, electrical and plumbing upgrades, etc. Achieving good thermal performance in an old house will likely mean stripping the interior side of exterior walls and applying closed cell spray-on insulation to fill all air infiltration paths and yield a sufficient R-value, more insulation in the attic along with replacement of windows with triple glazing. This is an overall energy conservation strategy. These actions will result in an energy performance as good as if not better than current practices. Renovation is always better than demolition. The real question is: How do we incentivize such a strategy so that waste can be avoided.

      1. “These actions will result in an energy performance as good as if not better than current practices.”

        The things you propose would be a big improvement but would fall well short of a current Vancouver code built house.

        No under-slab insulation.

        Thermal bridges everywhere.

        Spray foam in 2×4 cavity walls. Vancouver does not accept spray foam even in 2×6 walls as being sufficient to meet thermal performance.

        At some point there is little to nothing to be gained by increasing attic insulation. Hot air may rise but heat finds any path to cold.

        Really difficult to air-seal such places as joist-ends and joints between walls and floors/ceilings. Spray foam can peel off of the framing over time and leave air/moisture pathways that can be very destructive of the exterior framing. Plastic vapour barriers are still necessary, to be safe, but cannot be retrofit between framing plates as is done with new construction. So it won’t be as air tight as typical new construction which is still much more leaky than a passive house which uses a more robust strategy.

        The question is if it’s all worth it for an old house. Very difficult to justify the huge expense for a house that is more than likely past it’s half way point and would still be an “old house” without replacing so much of the embodied energy that resides within it. People want open plans and modern appliances if they’re going to go through the effort and expense. Loads will fall in new places – new foundations will need to be placed to accommodate them.

        Meanwhile much of the character in a character house cannot be replicated with modern energy-efficient windows.

        Teslas don’t have fins, bias ply tires or hood ornaments but you wouldn’t put aerodynamic door handles on an old classic either.

        The city may well have some power to encourage the retention of period exteriors but they are less inclined to interfere with what a homeowner will do inside.

        When people are willing to make such an investment it often comes with what we see all too often in Vancouver. Two stories of old framing suspended in air awaiting a new foundation. And a significant amount of that framing will be removed to modernize the layout after it’s been set back down.

        Absolutely there should be encouragement and incentives to perform energy retrofits. But meeting current code requirements is extremely difficult to achieve and it’s not correct to infer that you can meet or beat them under most conditions.

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