posted 2 years ago
I think that all wall assemblies have trade-offs. I agree with Max on many points, but hope this attempt to reframe the conversation is helpful.
If you want to build with ICFs (insulated concrete forms), and you detail the rest of the building well (start with passive solar design, adequately insulate floors and ceilings, air-seal windows and other penetrations, use efficient HVAC, etc.), you’ll at least have an energy efficient structure. For decades, this is what the conventional building world considered a “green” building. It was energy efficient, period. Little thought was given to material embodied energy, toxicity, or end-of-service life disposal. Thankfully, that is changing, and if you want to build with ICFs you can chose to go beyond the promise of energy efficiency that they offer.
ICF blocks made with virgin polystyrene beads and virgin plastic for the webs are probably the most common and least environmentally friendly. Some ICFs are better in terms of having a lower embodied energy, more recycled content, storing carbon, or all three. For example, Rastra makes ICF blocks from recycled foam and plastic, although Portland cement concrete and steel rebar still fills the cores. Nearly all of the used coffee cups and packaging materials for tools and appliances sold world-wide go into a landfill—so recycling this material into building blocks is a better solution. Still, recycled content or not, both types of ICFs rely on a petroleum-based foam. Faswal, Durasol, and now it seems Nexcem are among the ICF brands that use waste wood (presumably from pallets) to form the ICF blocks, but like polystyrene blocks, the cores are still filled with some combination of steel and Portland cement concrete. The wood chip ICFs store some carbon and offer the option of using rockwool to bump the R-value, but at the expense of strength. Using high fly-ash and other concrete mixes can help lower the embodied energy of any of the ICFs, but these mixes can be harder to find.
Laminate flooring, drywall, MDF, OSB, almost all petroleum-based foam products, fiberglass, caulk, vinyl, etc., are recognized by the conventional building industry as superior by different metrics, that unfortunately do not take into account toxicity or embodied energy. Many of these conventional building materials contain toxins, or have a very high embodied energy, are difficult to re-purpose at the end of a building’s service life, and worse. Lower installation cost, ease of manufacturing and transportation, widespread availability, thermal efficiency for a given thickness, and material and technique familiarity among building contractors play a huge role in their success and current dominance in the building world.
I’d love to see more wall assemblies using plant-based insulation materials like straw, cellulose, wood fiber, cotton, hemp, cork, wool (if you don’t count the middle step of growing on sheep!). I’d also love to see more distributed thermal massing from 1”-2” thick clay-based interior plasters.
Builders like me try to use more natural, low-embodied, non-toxic, locally sourced materials whenever possible, but we’ll also use conventional materials when there aren’t affordable or viable substitutes for code requirements like subfloor and stem wall insulation (rigid foam), fire blocking between rooms and floors (sheetrock), etc.
Still, I don’t regard green builders who use foam ICFs and SIPs (structural insulated panels) as “the enemy” even as I hope they rapidly transition towards non-foam alternatives like the above mentioned wood chip ICFs, and soon—block wall systems made with hemp or straw, or even straw SIPs.
Here’s why. According to the U.S. Environmental Protection Agency, each year in North America nearly 40% of ALL energy (including manufacturing, agriculture, and transportation sectors) consumed goes to heat, cool, and power buildings. The vast majority of this 40% is for heating and cooling! Another nearly 10% of ALL energy used in N. America goes to manufacture building materials.
I think it’s more constructive to look at ICFs as being on a continuum. If well-designed and built, an ICF building can be incredibly energy efficient, and thus help lower that 40% of all energy used in N. America. Those ICFs that also have a lower embodied energy further nibble away at the 10% of annual energy expended on building materials, and some are also less toxic or non-toxic, plus they store carbon.
We don’t have a lot of time to make a difference in the climate change picture. Some people think it’s already too late. I’m casting my lot with those who believe that it’s not, that we may have ten or twenty years to try to make a difference in the built environment.
The first thing we must do is build energy efficient buildings. If that’s all we do, and use mostly conventional materials to do it, we can at least stop using so much energy just to heat, cool, and light buildings. But we’ll reach our end goal much faster if we also substitute low-embodied energy, carbon storing building materials like wood, straw, hemp, cotton, bamboo, and use more lower embodied energy materials like clay. And to do that, we need to ramp up efforts to make designing and building with these materials easy and accessible.
Right now we don’t have enough knowledgeable and experienced designers, or builders, or even a sufficiently developed supply chain to support a rapid transition towards building with all- or mostly-natural materials. Until that happens, we need these “green” if not-natural building materials so long as they do in fact produce energy efficient buildings.
If we build energy inefficient all-natural buildings we really haven’t solved the problem beyond reducing toxins in our environment and reducing the embodied energy of our buildings. And that’s where I have a more nuanced view of the role that earthen buildings (rammed earth, cob, adobe, etc.) can play. Absolutely they are part of the answer to this challenge. These thermally massed structures perform very well in areas like the American Southwest, characterized by warm summers, relatively mild winters, and most importantly, consistently sunny days and cool nights that drive a diurnal temperature swing. Our ancestors in these places discovered that thick-walled (thermally massed) structures made from earthen materials were surprisingly comfortable almost year-round—a lucky coincidence of human ingenuity, diurnal temperature fluctuations, and locally available building materials. (Humans in other places found other building materials and techniques suited to their climates, too...think igloos for Eskimos, animal skins for Great Plains Native Americans, etc.) The thick earthen massed walls helped moderate interior temperatures as day temperatures soared and night temperatures plummeted. Cool in summer, not terribly cold in winter so long as mostly-sunny days help offset cold nights. Moving further away from the equator north or south we find that buildings of all kinds required more supplemental heat to maintain comfortable interior temperatures, and that’s still true. Today, that heat usually comes from burning either wood or fossil fuels.
If we could instantly replace all the housing in North America (and other parts of the world where they currently don’t use earthen materials for walls) with earthen buildings, we’d be burning A LOT of fossil fuels and wood to keep them warm. Or adjust our expectations and behaviors and wear more insulative clothing while indoors.
That shift towards more earthen walled materials might reduce the amount of energy we currently spend to manufacture modern building materials, but I think we’d need as much or more energy to keep those buildings warm during the winter. In most temperate and extreme cold climates, a structure that relies on thermal mass alone (concrete, cob, rammed earth, adobe, etc.) is quite uncomfortable during the winter unless it uses lots and lots of energy for heat—much, much more than if those buildings were also well insulated.
In summary, it’s not so simple as convincing nearly everyone to build with rammed earth or any other type of massed wall system.
Just yesterday I returned from the California Straw Building Association’s West Coast Natural Building Conference held near Nevada City, California. The conference site was a campus with many, if not most structures built by modern day earth building advocates David Easton and Nader Khalili (sadly, both no longer alive). Superadobe and rammed earth walls everywhere! Fantastic, inspiring, beautiful...and cold in early April without lots of supplemental heat. Rammed earth (and cob, adobe, super adobe, et. al.) is not a great solution in many temperate and most cold and extreme cold climates.
Jim Reiland
Many Hands Builders
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