"The Greenest Building is the one already standing", Carl Elefante's great line, has been the mantra of the green preservation movement, and I have used it a lot on TreeHugger. But while we knew it intuitively, we never had any real data. Until now, with the release of The Greenest building: Quantifying the Environmental Value of Building Reuse, released this morning. The report uses Life Cycle Analysis, (LCA) to compare the relative impacts of building reuse and renovation versus new construction.
The key findings show that the mantra is true, the greenest brick really is the one already in the wall, but with some caveats and qualifications.
This study examines indicators within four environmental impact categories, including climate change, human health, ecosystem quality, and resource depletion. It tests six different building typologies, including a single-family home, multifamily building, commercial office, urban village mixed-use build- ing, elementary school, and warehouse conversion. The study evaluates these building types across four U.S. cities, each representing a different climate zone, i.e., Portland, Phoenix, Chicago, and Atlanta.
Building reuse almost always yields fewer environmental impacts than new construction when comparing buildings of similar size and functionality.
The range of environmental savings from building reuse varies widely, based on building type, location, and assumed level of energy efficiency. Savings from reuse are between 4 and 46 percent over new construction when comparing buildings with the same energy performance level.
Now I must confess I was a bit shocked and disappointed when I saw those numbers in the lefthand column, only 9% to 16% reductions in climate change savings by keeping the old instead of building new. I asked Patrice Frey of the Preservation Green Lab and she pointed out that this was actually a big number,
In fact, replacing an average building with a new, more efficient building still takes as many as 80 years to overcome the impact of the construction.
Reuse of buildings with an average level of energy performance consistently offers immediate climate change impact reductions compared to more energy-efficient new construction.
As you can see from this graph, the blue line representing new construction produces a big carbon hit way up front; The orange renovation line produces a much smaller one. They don't cross for 42 years. So if the goal is to stop putting CO2 into the air, the orange approach is a whole lot more effective.
Materials Matter: The quantity and type of materials used in a building renovation can reduce, or even negate, the benefits of reuse.
This one is really interesting but makes sense. Some kinds of renovations, like a conversion of a warehouse to a residential, have so much new stuff going into an old frame that in the end, they are not even positive. The lesson is that we have to tread as lightly as possible, save as much as we can and think about the choices we make when we renovate, the amount that we do. There are developers who take an old building and seal up the windows, put in top of the line mechanical systems and new drop ceilings; there are others, like Jonathan Rose, who relies on opening windows and original surfaces. Two approaches, and two very different results. This is complex, dealing with what the report calls the Pre-energy efficiency measure’ or ‘Pre-eem’ case. It takes into account that " in many instances, older buildings have inherent efficiency strengths and perform on par with new construction."
Controversial Issues: Embodied energy
The report discounts a favourite approach taken by preservation activists, the discussion of embodied energy; that it took a lot of energy to make the building and you are throwing it away when you demolish it. As Robert Shipley put it:
Every brick in building required the burning of fossil fuel in its manufacture, and every piece of lumber was cut and transported using energy. As long as the building stands, that energy is there, serving a useful purpose. Trash a building and you trash its embodied energy too.
I have never been convinced, and wrote about it just last week in my post Embodied Energy and Green Building: Does it matter? From the report:
In recent times, many building and environmental scientists have been dismissive of the embodied energy approach to quantifying the benefits of building preservation; energy embedded in an existing building is often viewed as a ‘sunk cost.’ That is, it is often argued that there is no inherent current or future energy savings associated with preserving a building, because the energy expenditures needed to create a building occurred in the past, as did the environmental impacts associated with creating the building. In this view, the only value
of building reuse is the avoidance of environmental impacts that results from not constructing a new building. This approach has given rise to the avoided impacts approach to understanding reuse, which measures the impacts that are avoided by not constructing new buildings.
Or, as I noted,
Preserving and upgrading a building is far more energy and carbon efficient than knocking it down and building new. Calling the new building "green" when it replaces an existing building is a farce when it takes so much energy to build. But what matters is the embodied energy of the future building, not the past.
Report Raises as many questions as it answers
One important thing about older buildings: They are older. They have those qualities that Steve Mouzon talks about, being lovable, durable, flexible and frugal. It is hard to do a lifecycle analysis of a newer building when we have no idea how long it is going to last; the way a lot of them are built today, it seems unlikely that they will last the 42 years that it takes for them to pay off the carbon debt of their construction. The report gets this, writing in their suggestions for further research:
While durability data for some materials is fairly robust, it is substantially lacking in many areas, particularly with regard to relatively untested, newer materials. Better data and further analysis are needed to test the sensitivity of this study’s findings to different durability assumptions.
Then there is the issue of why they are being replaced. In most cases, it is because they are not high enough or dense enough, and one has to face the issue of "location efficiency", the theory that green-ness is directly proportional to density. The report notes:
Further research is needed to understand the relationship between density and environmental impacts as it relates to building reuse versus new construction. Additional density may be environmentally advantageous if buildings are located in areas that are walkable and transit accessible, thereby reducing the Vehicle Miles Traveled (VMTs) by occupants.
But the authors also realize that it is not so simple. When I asked Patrice Frey about this, she reminded me of Kaid Benfield's writings about Smart Density, and was kind enough not to remind me then of my own writings about what I call the Goldilocks Density.
Such an analysis should look at more than the carbon savings associated with reduced VMTs from additional occupants in a new building. Such studies should also consider the significant role that older buildings play in creating more character-rich and human-scale communities that attract people to more sustainable, urban living patterns.
That's just one of the ancillary benefits of preservation; another is the fact that renovation creates a lot more jobs than new construction, Renovation Uses Twice As Much Labor, Half as Much Material as New Construction, but that is beyond the mandate of the report.
It is the wonderful thing about this report, that even when it doesn't have all of the answers, it anticipates the questions. As a writer about sustainable design it backs up the arguments I have been making for years, and as a preservation activist, it gives me and everyone in the movement the ammunition we need to demonstrate that old buildings are green. We have all been waiting for this for a very long time.
Download it all at the National Trust for Historic Preservation