In April 2024, the National Trust for Historic Preservation held an online symposium on how preservation can mitigate the effects of climate change. The two-day event brought together speakers from across the preservation field (and beyond) to talk about ways to expand preservation’s role in climate action.

The building sector is responsible for nearly 40 percent of the carbon emissions that cause global warming. Broad, swift action is needed by the preservation community and others to reduce and eliminate carbon emissions from building construction and operations.

One of speakers at the symposium was Lloyd Alter, an architect, writer, and teacher based in Toronto, Canada. In May Alter released his second book, The Story of Upfront Carbon: How a Life of Just Enough Offers a Way Out of the Climate Crisis. Last month he spoke with National Trust Senior Policy Director Jim Lindberg about what “upfront carbon” means and how it relates to the work of preservation.

Looking for more resources on this subject? Check out our glossary of climate terms, and a resource reading list to help you learn more about cutting carbon.

What are the biggest sources of upfront carbon in buildings?

A lot of buildings contain steel and concrete, which are two of the most carbon-intensive materials. Half of all steel goes into buildings. And a great proportion of the concrete we make goes into buildings as well. The rest of the concrete and steel we make goes into building roads and bridges for cars to go between buildings and parking lots to store them. It is all “built environment emissions” and it is a huge part of the climate problem.

You've been involved in heritage preservation for many years. Do you see things that we might want to start doing differently to help address the climate crisis?

Our biggest challenge in the world right now is reducing carbon emissions. How do we do that with our old buildings? Well, for one thing, we can support decarbonization of the electrical supply. That happens through political pressure and legislation. We also have to loosen our standards about solar panels. You may not like the look of them on the roof of your building now, but they are reversible. Install them in a way that you can replace them when they get better in the future. The other thing we need to do is join the heat pump revolution and electrify our older buildings. Heat pumps let you switch over to all-electric building operations, and if that electricity is coming from renewable sources, carbon emissions come way down.

Switching from oil and gas systems to heat pumps can have a significant impact on carbon emissions. What about making older buildings more energy efficient? What are the best ways to do that?

We can do so much with light retrofits. We don't need to gut every building and put in six inches of insulation on the walls and replace all the windows and do all of this really expensive stuff that in many cases is wrecking the fabric and the things we love about these old buildings. You can make tons of difference by insulating basements and attics and doing good air sealing.

So is there a happy medium there where we don't try to take energy efficiency to the nth degree, which can be expensive and have a big impact on historic fabric?

We've wrecked a lot of old buildings by over-renovating them in the past. Doing things like putting a pile of insulation on the inside of masonry walls, making it so moisture can't get out of the brick, which then freezes and spalls and wrecks the building. We learned from that. I am a believer in the Pareto Principle, the 80-20 rule, that it is as hard to get the last 20 percent as it is to do the first 80 percent. For energy efficiency that means doing the basic stuff – attic and basement insulation, air sealing, storm window inserts, LED lighting – and then using heat pumps to make up the difference.

You’ve written a lot about materials and the technology of buildings. What are you seeing now that is interesting on that front?

With materials, what is happening in France and the UK is a revolution in stone. Instead of pouring concrete they're building with stone again. As someone I met over there explained to me, you can take limestone and crush it and can cook it at 1500 degrees and mix it with rock to make artificial stone –concrete. Or you just cut out the limestone and use that. It looks better, it lasts longer. It’s stronger and it creates virtually zero carbon emissions from manufacturing. Now we have x-rays and lasers and diamond saws and things like that, so we can work with stone and do things that people thought could only be done with concrete.

I know you were at the recent climate talks in Paris. What do you see in other countries that we could learn from?

There's something that's coming up particularly in France, but it's spreading. And that is the concept of sufficiency, which is really what my book is all about. It’s about asking the question: How much do we really need? We’re figuring out how to build highly efficient houses, but many of them are huge. We need to start measuring per-capita emissions instead of per-square meter emissions. We’re pouring massive concrete foundations and paving driveways and building new roads to get to “efficient” buildings.

What can we learn from our older buildings when it comes to sufficiency?

When I was president of the Architectural Conservancy of Ontario, my line was that historic buildings are not relics from the past, they are templates for the future. They show us how to build using much less upfront carbon. Our typical Main Streets and older neighborhoods were built using far less material than modern towers, which need monster concrete footings, columns, floors, elevator towers, steel framing, pipes. And older buildings are more resilient. If the power goes out, you can walk up the stairs, or open the windows.