PHribbon, a tool developed by British Passive House designer Tim Martel in the United Kingdom, has been adapted for American geography, energy sources, and, of course, archaic feet and pounds. It allows Passive House designers to calculate full life cycle carbon emissions for Passive House buildings and is now available from the Passive House Network (PHN) and Building Transparency. According to PHN:
Builder and comedian Michael Anschel once described Passive House as “a single metric ego-driven enterprise that satisfies the architect’s need for checking boxes, and the energy nerd’s obsession with BTUs”—and the nerds just got a lot more boxes to check. But I would explain to Anschel that it’s really important in this time of climate crisis, and here’s why:
According to the Passive House Institute, “Passive House is a building standard that is truly energy efficient, comfortable and affordable at the same time.” Thirty years ago, when Passive House started, being truly energy efficient was a major concern, but these days we are more worried about carbon. Thanks to their high energy efficiency, buildings designed to the Passive House standard are great at reducing operating carbon emissions and can be close to zero emissions with renewables.
Passive House
Passive House or Passivhaus is a building concept where heat loss or gain through the walls, roof, and windows is drastically reduced by the use of insulation, high-quality windows, and careful sealing. It’s called “passive” because much of the heating required is met through “passive” sources such as solar radiation or the heat emitted by occupants and technical appliances.
However, it takes energy to make building materials, move them around, and put them together into buildings. That is what is often called embodied energy or embodied carbon.
Architectural designer Finbar Charleson’s wonderful sketch for Architects for Climate Action (ACAN) says it all: above the line is the finished building; below the line are the power plants, freighters, transport trucks, cranes, factories, and mines that make all the stuff that goes into a building. All of those industries and processes emit carbon dioxide and equivalent gases, and added together are known as embodied carbon. According to the ACAN report, “The Climate Footprint of Construction,” it can total more than 75% of a building’s lifetime carbon emissions. I have written that it could eventually be even greater, in what I have called my ironclad rule of carbon:
I have never much liked the term embodied carbon because it is not embodied: It is in the atmosphere already, and every ton that we add comes off the 300 or so gigatons of carbon left in the carbon budget to stay under 2.7 degrees Fahrenheit (1.5 degrees Celsius) of heating. That’s why I prefer the term upfront carbon emissions. The term has become accepted for the product and construction stage, everything up to when the building is occupied, labeled A1 through A5 on Martel’s slide (above), but there are other sources of embodied carbon that come from maintenance and repair, as well as end of life. As the slide notes, they are pretty minimal compared to the orange and green upfront emissions.
Calculating embodied carbon has been difficult until recently. However, many new tools have been introduced in the last four years, including Building Transparency and their EC3 database, which was used by Martel to develop what’s formally called “PHN PHribbon by AECB CarbonLite.” According to the U.K. site, it is a Microsoft Excel add-on to the Passivhaus PHPP software.
As can be seen on Martel’s slide, you have to take information from a database like the EC3 (Embodied Carbon in Construction Calculator) that lists embodied carbon for different materials. You have to adjust for the electricity source using EPA data as different utilities in the U.S. have different CO2/kWh. The transport distances can be long and, as Martel explained to Treehugger, the difference between going by train and by truck can be huge. He noted also that in Europe it can be even more extreme; just moving a short distance between nuclear France and Germany can make a massive difference.
As I found when writing my book, “Living the 1.5-degree Lifestyle,” the carbon estimates can be wildly variable, and I had to often use European or British numbers. Even today, PHN notes: “The data inputs are by the nature of the emerging focus on embodied carbon values, incomplete. Industry-standard assumptions may be utilized. Where US data is unavailable, when appropriate, data or assumptions may be sourced from European sources such as the RICS Building Carbon Database.”
Architects and designers had better get used to this, as embodied carbon is creeping into regulations and legislation.
In Europe, France is regulating embodied carbon as of 2022. It has a clean electrical supply and as Vincent Briard of Knaug Insulation told Euractive, “In France, in new constructions, because of high energy performance of the building envelope and very low emission factor of electricity, embodied carbon could represent up to 75% of total carbon footprint and the remaining relates to heating and cooling.” As we have noted before, with a high-efficiency building and a clean supply of electricity, embodied carbon dominates.
Briard continued: “Norway, Sweden, Denmark and then Finland are all working on including the carbon footprint of the building, the embodied carbon and operational carbon, via regulation within one or two years, certainly within five.”
It is slowly coming into U.S., city by city and state by state, though it will take a long time, given the power of the concrete and steel industries. But it’s on the radar, the professional associations are considering it, and the concrete industry is laying out roadmaps for carbon neutrality. They know which way the wind is blowing.
Embodied carbon is the issue of our time; we should be measuring it in everything from our computers to our cars to our buildings. Because of the ceiling on emissions that we have to keep under to prevent heating above 2.7 degrees Fahrenheit (1.5 degrees Celsius), it matters now.
This is why I have been saying for years that every building should be built to the Passivhaus standard, and why now I would say that every building should be run through the PHribbon to calculate its embodied carbon. As Ken Levenson, the executive director of the PHN notes:
Let’s hope they all do because the upfront carbon burped into the atmosphere right now is more important than the operating carbon that dribbles out over the life of the building.
Here is Martel explaining PHribbon in fairly non-technical terms.
