They have their virtues, but concrete and petrochemical sandwiches shouldn't be on the green building menu.
Insulated Concrete Forms are a clever building system where two slabs of insulating foam are separated by plastic ties; you just stack them up, throw in some reinforcing bars if required, and fill with concrete. It makes a very energy efficient wall, the formwork is the insulation, and they are terrific in hurricane and tornado country. Many people consider them to be "green" because they provide such an energy efficient and durable wall.
Energy efficiency is a wonderful thing, but I have got into a lot of trouble with readers complaining that ICFs are polystyrene and concrete sandwiches, two materials that I am not particularly fond of. A typical comment was, "Apparently this d-bag has no idea what an ICF house is like in real life. Typical academic with no real world experience. Nice unimformed [sic] theories." Given that ICFs have their place (they make great basements), I have laid low on this subject for some years.Now, writing in Passive House Plus, John Cradden looks at the use of ICFs in Passivhaus buildings. There is lots to like:
ICF is certainly finding its advocates among energy-conscious architects and designers thanks to certain advantages that enhance its thermal performance, including inherent airtightness, the virtual elimination of thermal bridging and the fact that its advertised U-values are reliably achieved.
Cradden does write a paragraph noting some caveats.
While ICF certainly has its advocates, others may baulk at the fact that it typically comprises two materials which can have comparatively high environmental impacts: ready-mixed concrete and polystyrene. Both materials have relatively high embodied carbon emissions, although the question of how green ICF is may need to be based on a systematic sustainability assessment of the whole construction. Such an assessment could determine the embodied CO2 of a material, among other parameters, including a full life cycle analysis.
There are a few life cycle analyses that have been done, and they do show ICFs favourably. But as I noted in my review of one a few years ago, they don't compare apples to apples in terms of energy efficient walls; I complained that it wasn't even apples to oranges but apples to bicycles, comparing a 2x4 stud wall with fibreglass to a 12 inch ICF. Guess which is going to save more energy over its lifetime?
Embodied energy and Life Cycle Analysis
I suspect that if one did an LCA comparing a modern wood and cellulose Passivhaus wall to an ICF wall of the same R value and air tightness that one would get a very different answer. Take the embodied energy and carbon needed to make the product; the LCA study I read said, "More than 90% of the life cycle carbon emissions are due to the operation phase, with construction and end-of-life disposal accounting for less than 10% of the total emissions."
That just isn't true in Passivhaus designs. When insulation levels get really high, embodied energy of the materials becomes much more significant a factor than it used to be with less efficient walls, where operating energy dominated.
Health and toxicity
Then there are health questions. I know things are changing in Europe, but most foam plastics are treated with flame retardants (although the terrible one, HBCD, has been discontinued). They are petrochemicals, essentially solid fossil fuels. There are so many environmental issues with them, and it's not like there aren't alternatives that don't have these problems.
And don't even get me started about concrete, made from cement that's responsible for over 5 percent of the world's CO2 emissions, and aggregates that are responsible for habitat destruction around the world. I take the position that if you don't need it, don't use it.
There are also a few ICFs that try to address the issues. Durisol is one in North America and Velox looks like a similar product, made from wood chips in the UK. They are both concrete filled, but avoid the foams.
RecyclabilityJohn Cradden also raises the issue of recyclability:
The materials typically used to manufacture ICF – EPS, concrete, plastic ties and steel rebar – typically lend themselves to recycling once the building reaches its end of life, which was a significant factor in Irish firm Amvic gaining a BRE Green Guide rating of A+ on its system.
I would argue this. It is as recyclable as a Nespresso or Keurig pod; you can do it, the companies pretend to do it, but it is what Bill McDonough calls a "monstrous hybrid" -- far more trouble than it's worth and just phoney feel-good environmentalism done for show and to assuage guilt. Nobody is going to take these sandwiches apart.
I am not going to be as doctrinaire as I was a decade ago; ICFs have their place. I have seen systems like Legalett's where you can't help but admire the elegance of how it totally, seamlessly wraps the building in insulation. I can't argue with Cradden when he says ICFs go up quickly and neatly, and make a good durable wall that will last a long time. He makes it clear that ICFs have many virtues.
But I still believe that wherever there is a substitute, we should not be using concrete or petrochemicals in green building. Cradden notes that "passive house designers are generally agnostic when it comes to construction types because the focus is primarily on energy conservation." I don't think that is good enough; that's why I have, with tongue only a bit in cheek, proposed the Elrond Standard: Passivhaus + Low Embodied Energy + Non-toxic.
And that means concrete and foam sandwiches shouldn't be on the menu.