The Greenest Building: Retrofit or Passive House?


Yesterday, preservation rock-stars Preservation Green Lab released the results of a study on the energy impacts of retrofitting existing buildings versus building new ones. Their unsurprising–for an arm of the National Trust for Historic Preservation–conclusion: Retrofits are almost always greener than new buildings. Building Green picked up the story, as did Grist.

But…are the assumptions of the study biasing it toward that conclusion?

I know several folks at Preservation Green Lab (they are here in Seattle), and they are super-smart, committed people (smarter than me, no doubt.) Still, I’m skeptical of their conclusions. The stated assumption of 30% energy savings (for the advanced case!) is a very low bar. How would the results differ if in both cases the new and retrofitted buildings achieved Passivhaus, saving 90% of their heating/cooling energy instead of 30%? What if we compare retrofitting an existing building to Passivhaus standard with building a new one, also to Passivhaus standard? Or, the most likely real-world example, compare retrofitting an existing building to achieve a 30% energy savings (if that’s as far as it could feasibly get) to building a new Passivhaus building with 90% savings (that could be built for the same cost)? How would those scenarios pencil out, comparing Return-On-Investment? We already know its harder to get to Passivhaus with a retrofit. What if required zoning setbacks or fire ratings of materials prevent adding exterior insulation to the existing building, making achieving Passivhaus difficult or impossible, such that the only way to get to Passivhaus (get to 90% reduction, that is) would be to build new?

David Roberts (another smart Seattlite) laid out “the brutal logic of climate change” in a Grist post. (Required reading!) The Architecture 2030 Challenge, rightfully, has set out goals for the reduction of energy use in buildings that start with a 60% reduction today. Why are we even discussing 30% reductions?  As I said in my interview in The Atlantic, “The economic and social costs of climate change will be increasingly, staggeringly huge, and the longer we wait to begin [serious efforts at mitigation] the fewer resources we will have to work with…” As I tweeted last year, buildings built now to current codes will be worth less in 20 years–they are already obsolete.

The problem with new buildings is not that they are new, but that they are poorly designed. They are poorly designed in part because the means of financing new buildings favors large developments that max out the zoning envelope, rather than the finer grain, smaller buildings more often found in the kinds of existing neighborhoods we all love, and that will create the kinds of vibrant, transit-oriented, walkable dense urbanity we need to meet our carbon emissions goals. We need to think as hard about how to change the means of financing construction as how to build buildings that use less energy. Second, buildings are poorly designed because they don’t go far enough in their energy intelligence. They stop at the point they’re expensive enough to discourage their owners, rather than pushing harder and farther to get real savings. With Passive House we have to tools to reduce primary energy use by an average of 70% (depending on building type). Let’s start the discussion there, eh?

There are excellent reasons for keeping existing buildings: embodied memory, sense of place, appropriate scale…. I’m just not convinced saving energy is the unequivocal answer to the question of new versus remodel that this study suggests.

I’m looking forward to reading the report in detail, before I put my foot further in my mouth than I already probably have. After I get a chance to do that, I’ll update this blog entry to reflect my conclusions.

UPDATE January 30th.

I’ve had a chance to read through the entire study, and have a couple additional comments. From the study:

This groundbreaking study concludes that building reuse almost always offers environmental savings over demolition and new construction. Moreover, it can take between 10 and 80 years for a new, energy-efficient building to overcome, through more efficient  operations, the negative climate change impacts that were created during the construction process.

I don’t know about you, but I’d guess some would be tempted to read that and say “Well, dang, we better not build anything new then, eh? That so-called “energy efficiency” stuff is just more liberal hogwash!”

The all-caps “key finding” of the study is:


The footnote is:

“2. where energy performance for renovated and new buildings is assumed to be the same.”

Well (forgive me)…duh! If operating energy is the same for both new and retrofitted buildings, the only difference in total energy use is the embodied energy saved by reusing the existing building. Of course it’s going to “save energy” to use an existing building if you look through that lens.

The other issue is that an existing building (unless it is a single family house) will almost never replaced by a building of the same size and functionality. A one-story building in an urban village, for example, is not going to be replaced by another one story retail building, but by a five-story (“four-over-one”) apartment or condo over retail mixed use building, which also increases density, saving energy, and which makes transit feasible, again saving more energy. Liz Dunn’s own stunning Agnes Lofts project is a beautiful example of that kind of urban succession.

The authors do acknowledge that the study did not take those effects into account, but that doesn’t seem to have diminished the enthusiasm with which the press has embraced this study and repeated it’s “key finding.”