translated and editorialized (forgive me, Charlotte) by Sarah Cobb
Oh how we’d love to just say yes. Our hippy conscience is horrified by the sight of piles of polystyrene in the lumberyard. Yuck! Foam is gross, we think. But is it really? Should we banish it from the planet? Sadly, there is no easy answer. It isn’t as simple as a “Yes, because” or a “No, because” because there isn’t just one kind of foam. Should the question be which foam, where to use it and when? We’ll look at its impact on health, on the environment and on the characteristics of the material itself.
There are myriad ways of insulating in construction — mineral wool, fiberglass, cellulose, wool, denim, to name but a few, and then there’s foam; a petrochemical byproduct where polystyrene (the plastic used for CD cases) or urethane polymers are mixed with blowing agents to force the molecules apart, leaving tiny alveoles of air between them. Foam comes in a variety of formats, from pellets, to rigid panels to spray foam and each has its own properties.
Polyisocyanurate is often sold in panels covered with a thin aluminum film. Considered the most effective, it has an R-value (thermal resistance) of up to 7 per inch. Its insulating properties shrink, however, with dropping temperatures, rendering it drastically less effective at temperatures like -30 celsius. Its low permeance and aluminum face make for a mean vapour-barrier so it needs to be strategically placed in the wall to avoid humidity issues.
Extruded Polystyrene (XPS) is sold in panels (usually blue or purple) and is usually used in foundations because of its high density and its efficacy at all temperatures and humidity levels. Its R-value hovers around 5 per inch but it tends to lose its oomph over time. It was, and continues to be, more hazardous to the environment than any other foam because of its carbon footprint and blowing agents. These things are changing, however. More on that below.
Expanded Polystyrene (EPS) is a much less hazardous material. It’s most often pink and is used mainly in wall assemblies. Its permeability ranges from 3 to 5 per inch making it “semi-permeable”. Some varieties come with a vapour barrier (like Isolofoam’s Isoclad). Its R-value is lower than XPS’s at about 3.9 per inch but it’s also cheaper.
Closed Cell Spray Polyurethane Foam (ccSPF) is, as the name implies, sprayed with a gun. Usually made of two components, isocyanate and polyol resin, the combination of the two creates a chemical reaction that causes it to expand up to sixty times the volume of the liquid. The result is a foam that eventually hardens, that averages R6 per inch with air cells that are completely closed. In its drying phase, ccSPF offgasses some pretty toxic VOCs. Its application requires precision and specialized equipment which is why only pros certified by the CUFCA (Canadian Urethane Foam Contractors Association) can apply it. These VOCs and the application hazards partly explain why opinion is so strong about this insulation’s effects on health. There are newer polyurethane options (like soya) with a slightly reduced carbon footprint and, as with polystyrene, ccSPF’s greenhouse-gas-heavy blowing agent is on its way out.
Open Cell Spray Polyurethane Foam (ocSPF) is similar to its closed cell counterpart but is much less dense, leaving much bigger and connected air pockets between cells. It is softer and easy to squish between your fingers, essentially the same foam that is used for packaging. Its insulating capacities are reduced (to about R3.7 per inch) and the blowing agent is generally water-based which gives it a better environmental report card than closed cell spray foam. It is also considerably cheaper.
Foamglas is a cellular glass insulation made from 60% recycled glass and other materials. The ingredients are mixed, smelted and the resulting glass is cooled, crushed and powdered, loaded into stainless steel trays and heated to 850o creating hermetically sealed vacuum cells of molten glass. It’s then cut into panels. Offcuts go back into the production process. It’s non-combustible and non-toxic. The R-value is around 3.4 and it’s triple the price of XPS. If cost is no issue, Foamglas is the one to beat. If you can find someone to sell it to you.
People tend to think that foam is completely awful for the environment. But what does that really mean? Is the culprit its extraction, its transformation or its application? It’s important to understand the ins and outs to separate myth from reality, which is easier thanks to Green Building Advisor’s graph comparing the ecological footprint of different insulations. Foam gets its bad name primarily from the toxicity of its blowing agents. Although not all foams use the same gas to expand, they all need a blowing agent for expansion, the process which, at its essence, defines a foam; a molecule derived from petroleum which is modified (polymerized) and combined with a gas to make it swell. With open cell polyurethane and most expanded polystyrenes, the blowing agents are water-based and therefore don’t represent any kind of harm to the environment. Until 2010, the gas used for other types of foam was a Chlorofuorocarbon (CFC) which damages the ozone layer. The Montreal Protocol of 1997 banned CFCs and replaced them with Hydrofluorocarbons (HFC) — principally 245fa, used in closed cell polyurethane and 134a, used in XPS and also as the coolant in car air conditioning systems.
The Global Warming Potential (GWP) is another metric for comparing the global warming impact of different gases. Specifically, it is a measure of how much energy the emissions of one ton of a gas will absorb over a given period of time relative to the emissions of one ton of carbon dioxide (CO2). HFCs like 245fa have a GWP 1040 times higher than CO2 while 134a’s GWP is 1430. HFC-based blowing agents are considered accelerators of global warming, referred to as high-GWPs, making them very unpopular with anyone interested in the health of the planet. Certain foam manufacturers have been working on a blowing agent based on Hydrofluoroolefins (HFOs), — gases with similar qualities as HFCs but with a much lower GWP — (1.6 for Dupont’s Opteon 1100 and 1 for Honeywell’s Solstice). Despite the manufacturers’ move toward greener options, HFC can still be found in XPS and SPFs on the market but it won’t be long before all HFCs will have been replaced by HFOs, eliminating the threat blowing agents pose to the environment.
When we talk about ecological footprint, we often see the term “embodied energy” which represents the hidden energy cost of manufacturing, extraction, transformation, production, transport, maintenance and recycling of materials — in sum, all of the energy required throughout its life cycle. Building Green attributes an embodied energy rating of 72 MJ/kg (megajoules per kilogram of product) to all spray polyurethane and polyisocyanurate and 89 MJ/kg for polystyrenes. Cellulose, which clocks in at 2.1 MJ/kg is therefore, respectively, 36 and 42 times lighter on the planet. But it’s not that straightforward. Embodied energy isn’t in direct proportion to CO2 emissions because not all energy sources cause the same CO2 emissions (think coal power vs. hydroelectricity) or have the same environmental impact. Also, there is more than one step in production and each of those steps has its own CO2 emissions. That’s why we should rely more on the carbon footprint metric, that is to say the number of kilos of CO2 produced for each kilo of material. For example, for each kilo of polyiso or SPF manufactured, 3 kilos of CO2 is emitted. The carbon footprint of polystyrene is 2.5 kilos of CO2/kg, making polyiso/SPF 28 times worse and XPS/EPS 24 times worse than cellulose at 0.106kg CO2/kg. But there is even more to it. Different insulations have different R-values and so one needs a great deal more of certain insulations like cellulose, pink fiberglass and open cell spray foam to get the same level of insulation as, say, XPS or EPS or closed cell spray foam. Total CO2 emissions must also reflect the quantity of insulation to achieve the same R value to paint a true picture of the environmental impact. Taking R value into account, the ratio of cellulose to ccSPF is more like 1:12, meaning SPF is twelve times worse than cellulose. Bad but certainly not as bad as the initial 1:36.
Foam cannot be recycled. It cannot be reintroduced into the same production cycle or even transformed into something else. Each petroleum molecule used in production is lost forever. When we talk about recuperation what we’re talking about is construction material recycling plants taking it and disposing of it by compacting it and burning it, which, if not done at more than 1000 degrees celsius, releases a host of toxic gases into the environment. Apparently most incinerators don’t get hotter than 900o. It’s a laborious process because foam is light but incredibly bulky (the same properties that make it so insulating) so transporting it and dealing with the waste is very costly, for society and for the environment. Thankfully, foam can be partly made from recycled products which somewhat reduces its carbon footprint. Airmetic Soya by Demilec, for example, is 40% recycled plastic bottles and renewable vegetable oil.
Despite all these efforts to green the product there is no denying that petroleum-based insulation cannot (for the moment) be as ecological as something like cellulose. It’s worth noting, however, that some foams have a smaller carbon footprint than mineral wool, the extraction of which (volcanic rock) is seriously damaging to local ecosystems. It’s also worth acknowledging that foam used in construction today is nowhere near as bad as it used to be and seems to be improving all the time.
All insulation made from petrochemical products offgas Volatile Organic Compounds, compounds like formaldehydes and amines that are toxic and polluting both during their manufacturing process/installation and drying. Installers of spray polyurethane have to wear full protection (sealed coveralls, fine particle mask sometimes even with a fresh air intake). In 2013, a number of US lawsuits were filed by homeowners against manufacturers like Demilec. The suits alleged that the residents of homes insulated with these products developed neurological and respiratory problems as a result of faulty application of the product. Toxic VOCs were being released for longer than expected so residents had moved back into their homes before the VOCs were “neutralized”. Everyone acknowledges that the application of spray polyurethane is rarely done in optimal conditions, often with crappy equipment by badly trained workers who are poorly informed about the contents of the product and appropriate safety measures. Spray foam that hasn’t been applied properly may never really “set” and can continue to offgas VOCs forever. It’s worth noting that the majority of complaints involved open cell SPF. In 2016, the four biggest chemical companies in the US (Dow Chemical among them) were sued for having withheld information from the Environmental Protection Agency (EPA) about prior knowledge of the harmful effects of isocyanate products (used in both polyisocyanurate and polyurethane). As little as one drop of the isocyanate’s raw ingredients (methylene diphenyl diisocyanate, polymeric MDI or toluene diisocyanate) on the skin can cause respiratory injury in humans. On top of being irritants for both skin and mucous membranes, isocyanates contain known carcinogens. As for the blowing agents, thankfully most of the new ones coming to market are free of VOCs.
Petroleum-based insulations, as one would expect, aren’t exactly fireproof. Footage of the Grenfell Towers going up in flames is a case in point. The exterior siding of the building was made of extruded polyethylene covered with aluminum on both sides. Polyethylene is extremely flammable and that, combined with the air gap left behind it for ventilation, created a chimney effect that quickly turned the building into a towering inferno. Other petroleum-based insulations are no different. However flame retardants or fire-resistant ingredients can be added to raise the temperature at which the foam ignites, which is the case with most foams whether they are sprayed or in panels. Despite that, any material made of plastic, if exposed to high enough temperatures will end up combusting. To make matters worse, burning foam releases toxic gases that are themselves flammable. The Net Zero Alstonvale house in Hudson burned to the ground the day the polyurethane was sprayed. The cause of the fire was attributed to the great quantities of flammable fumes released during installation. For more horror stories visit the Green Building Advisor website.
ITS USE IN CONSTRUCTION
Because each kind of foam has its own physical and chemical characteristics it’s next to impossible to establish a general rule about its use inside buildings. The role it serves most often is as an exterior blanket to break any thermal bridges (a temperature transfer that occurs when a conductive element of the exterior links directly to the interior). Even in this role, no two foams behave the same way. Each has a perm rating which indicates its permeability to water vapour. Certain foams, like polyisocyanurate panels faced with aluminum are considered a Class I vapour barrier (.1 perms or less) while EPS and open-cell SPF are considered Class III (from 1 to 10 perms). It isn’t enough to know the characteristics of the category (e.g., polyiso, EPS, XPS, etc) of foam, one needs to know the specifications of the actual product. If certain guidelines aren’t respected it could mean unwanted (read disastrous) results. Each product should be chosen according to its position in the wall composition so that it can’t hinder its drying potential. Humidity (from green wood or other building materials) always finds its way into a wall and preventing it from finding its way out could have catastrophic results. A house built here in Quebec, for example, would normally have a vapour barrier on the inside (just behind the drywall) meaning the drying route is to the exterior. If some unwitting future owner wanted to boost the performance of the house by adding a really low permeability product to the exterior (say a layer of polyiso), the path to drying would be eliminated and the potential for high humidity levels in the wall go way up and there are plenty of construction materials like OSB that really don’t deal well with humidity. In a different application, the impermeable nature of foam can be a bonus if the goal were to use it as a vapour barrier, say to foundation walls.
There are two schools of thought when it comes to dealing with humidity in walls. Dr. John Straube, with his 5 Ds of moisture control (Design, Deflection, Drainage, Deposition, Drying), is of the opinion that a house that is perfectly vapour resistant that will never have any humidity introduced into the wall is an impossibility. He suggests that it therefore makes more sense to provide places for humidity to be deposited in the wall and to use materials that are hygroscopic (which store humidity and slowly release it) allowing the wall to dry out. Materials like cellulose, clay, hemp or cotton could be used as “moisture batteries” to guard against potential defects in the building without compromising the integrity of the building materials (like mushy OSB) or the structure itself (rotting sills). For a wall composition to work, the drying potential of a material must exceed its capacity to store humidity or the long-term viability of the wall is compromised.
Others posit that one is better off using hydrophobic materials that have zero potential for humidity absorption to prevent the wall from hanging on to moisture. Perhaps in a climate where relative humidity levels are always high (where the drying potential is limited) this approach makes sense. But everything comes into play. The orientation of the building, the climate, the habits of the inhabitants and a host of other factors can impact the building materials. That is what ecological builders are talking about when they use the term “holistic” — seeing the building as a whole rather than following a prescription which may be very ideally suited to one set of parameters and not another. All the variables, not least of which their influence on each other, need to be taken into account to make a wall composition that is going to last.
In all cases, evaluating how the material will react to temperature and humidity variations, even if it’s unable to “stock” moisture, is critical. Different foams perform differently if they are too cold or too hot or even too old. If foam is used in an intelligent and considered way, it can be a tool for good in building science.
With all these variables it’s complicated to say unequivocally that foam is good or bad. There is no doubt that foam is hazardous to health and that its environmental report card could use some improving but the industry is adapting. It’s just a matter of time before polystyrene and polyurethane products with acceptable GWP numbers hit the market and surpass fiberglass and mineral wool as the more eco options. There’s no denying that in certain applications, like under concrete slabs, with the exception perhaps of foamglas which is triple the price and half the R value we just don’t really have other good options. Without the luxury of doing away with it entirely, perhaps, like an irritating brother-in-law, all we can do is learn to embrace the love-hate relationship.