There is a plethora of home improvement shows demonstrating how easy it is to buy, renovate and flip a house, and make some easy coin in the process. And when there is insulating to be done, it often seems people gravitate towards spray foam insulation. Why is that? Well, it works - at least in some ways.

Spray foam manufacturers’ marketing departments have worked very hard to distract us from the potentially sketchier aspects of spray foam. This has been quite successful, as it has become a very popular insulation choice for renovation projects, and even some new home builds as well. 

One angle that is heavily promoted, is the airtightness that can be achieved with spray foam insulation. This has been a great strategy to secure market share as many areas of Canada and the US are adopting more stringent requirements for making homes airtight - but from experience spray foam can age poorly, and shrink or separate - in which case it's no longer airtight.  

The advantages of spray foam insulation

When installed properly, spray foam can help make a house airtight (when first applied); it works as a vapor barrier and it adds a significant level of insulation to a home, further reducing the energy needed for heating and cooling. An all-in-one product for home renovation that provides the insulation, air barrier plus vapor barrier is, at least superficially, a very appealing product.

A lot of the discussion we’ve seen online this year is about how good spray foam insulation works, and how ‘sustainable’ it is. The ‘greening’ happened because spray foam manufacturers in Canada were obliged to switch to climate safe blowing agents on January 1, 2021 by the regulatory elimination of HFCs, driven by the Kigali Amendment to the 1987 Montréal Protocol.

This created the perfect opportunity to talk up spray foam as an ‘eco-friendly green insulation’, even though quite a few manufacturers just squeaked into compliance with the new regulations at the very last minute.

We do like to give credit where it's due, and we did write about Demilec's switch to the climate-safe spray foam blowing agents back in 2017. That was well ahead of some other well-known insulation manufacturers who just kept on pumping out the old HFC blowing agents, which were as much as 1,430 times worse in Global Warming Potential. 

Global Warming Potential, or GWP, is a measure of how much heat-trapping potential a substance has, compared to carbon. A GWP of 1430 means that a given unit of a substance is that much worse than carbon as a heat trapping gas when released into the atmosphere.

The new HFO (hydrofluoroolefin) blowing agents have a GWP of 1, which basically means that insulating 1,430 houses now with spray foam will do the same atmospheric harm as was done by 1 house in the past. You don't need to be a mathemagenius to know that's a pretty impressive improvement. So we do extend a big thanks at least to Demilec, for being 4 years ahead of the curve. 

All the good stuff aside, there are still ecological issues with this 'miracle' multi-purpose insulation product, and we are a bit disturbed to see it gaining such a strong market share in the mainstream building industry without much in-depth discussions or balanced and experienced views about the downsides of spray foam insulation. So....time for a look as the less appealing aspects so we can all make informed decisions. 

The disadvantages of spray foam insulation as a green building product

Regardless of the adoption of more eco-friendly spray foam blowing agents, there is still the matters of air quality, building durability and end-of-life disposal of the product itself and anything it touches.

The biggest problem we have with spray foam from a sustainability standpoint, is that it is undeniably made of toxic chemicals, some of which will pollute the indoor air long after owners take occupancy of a home.

And once it is applied to a substrate, it is extremely difficult to remove it. If you do try to reclaim wood or other materials that have been coated with spray foam, it can create a toxic dust in the process which can be very dangerous to those carrying out such work. And aside from just the health risks, simply the cost of trying to salvage spray-foamed materials is the reason they will virtually all end up in a landfill. 

Spray foam and wood end up in landfills because it is almost impossible to remove
Once spray foam has adhered to a substrate like framed walls, roof decks and subfloors, it is almost impossible to remove. So building materials that would otherwise have been recyclable or reuseable will end up in a landfill. 

Even now while the price of lumber is astronomically high - and so motivation is high to recycle and reuse wood as much as possible - it’s still very difficult to justify the cost of paying someone to scrape foam off a 2x6. So if it isn’t happening now, you know it’s not going to happen when the price of lumber drops back to a more familiar range. 

What are the toxic ingredients in spray foam insulation?

The ingredients in spray foam typically include isocyanate and polyol, with a smattering of blowing agent and additives like toxic flame retardants. The polyol, which is mixed with isocyanate to form polyurethane is, in general, a relatively harmless alcohol compound and is primarily added for greenwashing PR reasons as it can be made with soy and other natural oils.

Unfortunately, this tiny amount ( between 2 and 4%) of GMO soy or plant based oil is dwarfed by the toxic soup of other ingredients in SPF wood. But it only takes adding 2% of something non-toxic to justify basing 100% of the marketing around it so people think their homes are insulated with something akin to tofu. 

Spray foam insulation disadvantages toxic chemicals fumes off gassing
A typical safe handling manual first page for spray foam insulation - not overly-reassuring


Isocyanate often comes from methylene diphenyl diisocyanate (MDI), and the manufacturing of MDI includes such ingredients as benzene, chlorine compounds and formaldehyde. This combination of chemicals emits a disturbing concoction of dioxins and furans, carcinogens, bio-accumulative toxicants, and endocrine disruptors. 

That MDI is one of the chemical ingredients that are mixed on the jobsite which, together, react to create the final spray foam product. Read between the lines here - a freshly trained spray foam installer is suddenly assuming the role of a chemical engineer and spraying stuff in the place you will soon live. That should give anyone cause for concern, as MDI is a known allergen and sensitizing toxicant. Don't just take our word for it, here's what the EPA has to say about the human health implications:

“Diisocyanates are well known dermal and inhalation sensitizers in the workplace and have been documented to cause asthma, lung damage and, in severe cases, fatal reactions."

The really scary part, is that once you have been ‘sensitized’ from exposure to MDI, it can lead to the development of chemical sensitivities, and even the tiniest subsequent exposure in the future can have severe health effects.

The catalyst for the reaction/curing is often an amine compound or lead naphthenate. Amine is derived from ammonia, and can produce the fishy off-gassing smell that is often reported in homes sprayed with this type of foam insulation. The Alliance for the Polyurethanes Industry has this to say:

“Many amine-based compounds can induce histamine liberation, which, in turn, can trigger allergic and other physiological effects, including bronchoconstriction or bronchial asthma and rhinitis."

"Systemic symptoms include headache, nausea, faintness, anxiety, a decrease in blood pressure, tachycardia (rapid heartbeat), itching, erythema (reddening of the skin), urticaria (hives), and facial edema (swelling). Systemic effects (those affecting the body) that are related to the pharmacological action of amines are usually transient. Typically, there are four routes of possible or potential exposure: inhalation, skin contact, eye contact, and ingestion.”

Lead naphthenate may also have effects on the central nervous system and kidneys and it is advised that pregnant women avoid exposure. The National Institute for Occupational Safety and Health (NIOSH), a division of the CDC, states: “It is strongly advised that this substance does not enter the environment."

Spray foam insulation and internal air quality in homes (IAQ)

There's no escaping the fact that spray foam is a petroleum based toxic chemical concoction that is sprayed on the inside of walls, making them not just well insulated, but very airtight as mentioned earlier.
Different manufacturers and installers of spray foam will insist that occupants vacate their homes - anywhere from 24 to 72 hours are the recommendations we’ve seen - to allow the foam to fully cure and off-gas. Are we to assume then, that after that time period - somewhere between 25 and 73 hours - that the human health risks are all gone?

That would be the natural assumption, but rarely would that be the reality in our opinion. In all likelihood, the success of the ‘eco-friendly spray foam’ marketing campaign has led a lot of occupants to re-enter their homes after the allotted time for chemical off-gassing has ended, with the assumption that the air is safe to breath. We find that disturbing.  

In reality, what we've been reliably informed of, is that these indicated curing times are what you could expect "under ideal conditions". But even after some digging, we have so far been unable to successfully alleviate our concerns that these ‘ideal conditions’ are always being met.

According to manufacturers, the ‘ideal conditions’ include maintaining the right ambient temperature, suitable humidity levels, and a very specifically-mixed chemical ratio. There is nothing there that makes us comfortable with this, because rarely does anything in on-site construction work out exactly as planned and rarely does it stay on schedule.

We have seen spray foam being applied in wide ranges of temperatures and humidity levels, and none of us have ever heard an installer say they needed to delay their work to protect the future air quality of the home they are spraying. If that were to happen, then pricing would be much higher to account for lost time if installers only worked during ‘ideal conditions’.

Every year there are numerous legal cases involving uncured foam rendering homes uninhabitable making their way through the courts, including this one with over $2.5m damages awarded for "life-altering serious injuries as a result of exposure to chemicals". This home in Canada was made unlivable due to fumes from a spray foam job, forcing residents to spend months living in a camper in their laneway. 

Let's assume the best for a moment, and imagine a case where everything worked out perfectly and the foam was mixed and sprayed with the precision of Michelangelo painting the ceiling of the Sistine chapel.

Where, in such ideal conditions, will the toxic chemicals off-gas to? Well, that’s simple. Hopefully some will off-gas to the exterior, but without a doubt much of it will off-gas into the newly built ‘airtight’ home. Let the reality of that sink in for a second. 

Not every spray foam insulation installation goes according to plan
Not every spray foam insulation installation goes according to plan...

Where it gets worse, is when you consider where spray foam tends to be used – smaller jobs where the overall cost increase may be more acceptable such as tiny homes, shipping container homes, and basements. Tiny house builders often don’t include ventilation systems, leaving you penned in with your newly sprayed chemicals, and certainly no off-gassing will occur to the outside with metal boxes and concrete basements.

Virtually no air will leak through spray foam after it sets (right after, at least) and as much as we advocate for airtight homes, that can be a very real problem in this case given the risk to health. It is a known fact that indoor air quality in homes can be heavily polluted, and several times more toxic that outdoor air. That’s another stat straight from the EPA.

So, in the scenario of spray foam insulation being added during a renovation - if that's what you decide to use - then at the very least we’d strongly recommend the inclusion of a good HRV or ERV ventilation unit as well, to more quickly bring in fresh air without using excessive energy.

Building houses airtight is great for energy efficiency, but that makes it all the more urgent to protect your home air quality by choosing non-toxic building materials. And given that some spray foam manufacturers have safety manuals as long as 84 pages and multiple hazard data sheets about how to protect yourself against adverse health effects from the chemicals in their "green" spray foam products, we think that’s a good reason to be concerned. Compare that 84-page safety manual to a natural wood finishing oil who’s health instructions recommend ‘not drinking it’ and… “if ingested, seek medical attention, IF you don’t feel well”. 

There is a disturbing increase in asthma rates in children, as well as various respiratory issues in people of all ages, and the air quality of our houses is the biggest source of contaminants that we breath.

This was always the case, but it has become an increasingly urgent issue now as many people have adapted to lock downs and working from home. So more renovations are happening, and people are spending far more time at home now, and many are building offices to work from home either full or part time moving into the future.

Is spray foam insulation really airtight?

Yes, spray foam seems to be airtight after it has set. But will it stay that way? That’s not as clear. Spray foam insulation is a liquid that adheres to surfaces (wood-framed walls as the common example), then expands and hardens. One thing it is not known for, is flexibility. And one thing that all buildings will need, is a little flexibility. Houses move; end of story.

Concrete expands and contracts, it heaves and cracks, and there is nothing you can do to stop that. You can reduce the severity of the impacts, but forever at some minor level, concrete will move. And if concrete moves and shifts, then you know for sure the wood walls that sit on it will be moving and shifting too. They don’t move a lot, or even noticeably, but minor ground shifting and wind pressure exert enough pressure on buildings that a lack of material flexibility can lead to reduced efficiency and durability.

How air leaks through spray foam

Wood studs arriving on a construction site are almost always wet, and they are usually left out in the rain until needed. So if they weren’t wet at first, they will be soon enough. Framed house walls will also spend weeks or more standing in the rain getting saturated with moisture before exterior weather barriers and roofs protect them from the elements. 

That means spray foam is applied to wood framing members with absolutely no consideration of the moisture levels of the wood. And what happens when wood dries? Well, it shrinks. And what happens if something solid is stuck to it isn’t flexible? Well, it cracks.

We have no doubt that in the beginning when all the chemicals are off-gassing from the foam into your house, that the foam is airtight enough to keep the toxins inside while it off-gasses, but as the months and years pass and the wood dries and cracks, will it retain its original airtightness? Not likely in our humble opinion.

We are fully aware that no house is perfectly airtight, but the more adaptable (flexible) a product is, the more chance it will withstand the normal movements that happen in buildings, which most people are not aware is even happening.

Is spray foam recyclable?

Currently, not really no. I’m sure someone somewhere has come up with a creative use for old bits of spray foam, but for the most part it will be heading to a landfill at the end of its life. Wood studs are recyclable, plywood is recyclable, rigid foam insulation boards like EPS are recyclable and even reusable, but anything with spray foam stuck to it is in all likelihood going to the dump. That means any wood, concrete or plastics that it is adhered to that could have been useful will fill up a landfill. 

So what is our conclusion on spray foam? It is, on one hand, a great product for certain precise applications. That would include insulating rim joist cavities in basements or small individual uses on a case-by-case basis. But on the whole, it is very difficult for us to consider this in anyway a green building product, even considering the new blowing agents. We conclude that partly because of the potential for air leakage through long-term shrinking, but mostly because of the potential health effects from chemical exposure, and the fact that the final destination for anything it touches is in all likelyhood, the dump.

The key to any successful build begins with thoughtful design and building material selection. Right on the heels of that as a priority, is choosing a higher quality and competent builder.  See our page here on how to find green home building general contractor, because they aren’t all the same. Some will cut corners, some will not. And that, is the premise of this article. There are aspects to building with spray foam that make the consequences of taking short cuts riskier than with other insulation, air and vapor barrier materials.

We would strongly recommend that if you are considering insulating your home with spray foam that you use a professional installer and resist the temptation to try the DIY spray foam kits - and carefully vet professional spray foam installers. Ask for references, ask about installer training, and ask how aware they are of the dangers. If they dismiss your concerns and tell you it’s perfectly safe, then you know they don’t take it seriously so hang up and call someone else. 

Now you know more about spray foam insulation and its impact on indoor air quality and landfills. Find more pages about sustainable construction below and in the EcoHome Green Building Guide pages.

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