Sustainable Alternatives to Spray Foam Insulation

I’ve recently noticed people installing spray foam insulation . . . despite being in the “sustainable building” movement. But spray foam is bad for the environment, and dangerous for your home.

I get why it’s popular. Spray foam’s insulating properties are hard to beat. It doubles as an air-sealing layer, and it can create a “warm” roof without the need for venting. That mitigates concerns about dew points. Plus, it’s pretty affordable. 

But if we consider the safety of our homes and the wellbeing of the planet, spray foam falls woefully short. It’s counterproductive to our goals. 

So it’s important to explore sustainable spray foam insulation alternatives.

Why is Spray Foam Insulation Bad?

Hazardous Materials & Installation

First off, installing spray foam comes with significant health risks. 

The chemicals off-gas toxic VOCs, so installers have to use respirators and protective gear. They’re basically hazmat suits! It’s not reassuring when our builders have to protect themselves from poison while building the structures we’re going to spend our lives in. 

The building usually has to be vacated during installation. And this off-gassing can continue for a few days after application. Talk about bad indoor air quality!

Will Spray Foam Stop Water?

Well, it’s true that spray foam doesn’t attract moisture. 

But if it’s not installed correctly—like if it doesn’t adhere to surfaces, or if it’s unevenly applied—spray foam is bad at creating an air-tight seal. Warm, humid air can seep in, and then condense on cooler surfaces. Now you’ve got water trapped in your walls. 

That’s how spray foam insulation can cause mold growth and wood rot. As the wood rots, it loses strength. You might notice sagging floors and warped walls. The structural integrity of the entire building can even be compromised. 

Not to mention, having mold in your walls can lower your indoor air quality and lead to health problems.

Spray Foam Shrinks and Cracks

All building materials expand and contract with weather, temperature, and time. Spray foam is no exception. The problem with this is that, as it expands and contracts, it sometimes cracks and crumbles. There goes the “air-tight sealing layer” we thought it would provide! Not to mention its insulative value is reduced—sometimes by a lot.

Spray Foam and Mice

While spray foam can seal gaps and cracks, making it harder for mice to enter, it's not entirely rodent-proof. Determined pests can potentially chew through spray foam, especially if it’s not installed perfectly or if it has shrunk or cracked over time. 

Although spray foam's durability might make it a better deterrent than some other materials, it’s still essential to take additional pest control measures and ensure proper installation to minimize rodent entry.

Spray Foam is a Fire Hazard

Spray foam is bad news for those who live in wildfire regions. Not only is it flammable—we could accurately call it a fire accelerant. 

In tests, spray foam ignited much faster than cellulose and fiberglass insulations. It reached flashpoint in under a minute (which means that it created toxic vapors, which then ignited in the air). 

It also created a thick, heavy, toxic black smoke mainly consisting of carbon monoxide.

Spray Foam is Bad for the Environment

The production process for spray foam involves high embodied carbon. It’s anything but sustainable!

Once its life in the house is over, its life in the landfill is just getting started. No one knows exactly how long it takes for used spray foam to break down, but experts’ best guess is several hundred years.

So it’s not a long-term solution for thermal insulation or air-tight barriers. It’s eventually (sooner rather than later) going to compromise the integrity of our homes, and wind up in a landfill. 

I sometimes wonder what our world would look like if everyone had to deal with their trash and waste at home—either in their town, or on site where they live. Right now, our waste is processed at centralized systems that usher it out of our sight. It’s sent off to where we don’t have to see it or smell it, to where it can’t poison our direct experience of land and water. 

We don’t have to see the pollution it causes too directly. 

If we did, what kinds of decisions would we make? 

Think about the products you’ve used throughout your whole life. How many of them would wind up in a landfill? How big would the pile be? How long would it last before it biodegraded? What would not decompose or feed the earth? 

Are there more eco-conscious alternatives you can use instead of those products?

Eco-Alternatives to Spray Foam Insulation

Let’s get to the fun stuff!

I’m encouraged by the innovation I see in the Natural Building movement! New advancements are coming along every year, giving us more efficient ways to insulate our structures without the dangers of spray foam. 

Air Barrier Alternatives

• Continuous Interior Plaster

This method involves applying a continuous layer of plaster on the interior walls, creating an air barrier. It's a traditional technique that's gaining renewed interest because it’s so simple and effective. But it’s also labor-intensive. It takes a skilled craftsman a long time to apply a smooth, even layer. That raises the cost.

• AeroBarrier

This is a mist that fills gaps and cracks to create an airtight seal. It’s a high-tech approach that can significantly improve the air-tightness of a building envelope.

• High Performance Membranes and Tapes

Companies like Siga and Pro Clima have developed some game changing air sealing products. These membranes and tapes are designed to fit snugly around doors, windows, and other key leak areas. Some tapes even have low permeability ratings that are great for breathable wall systems.

High R-Value Natural Insulation

R-value measures how resistant a material is to heat flow. So the higher the R-value, the better it prevents heat transfer. And if we have a higher R-value (or more insulation), we don’t need to be as concerned about dew points. (The dew point is the point at which air becomes so saturated with moisture that it starts condensing on surfaces. We want to keep that point outside of our buildings, and good insulation helps with this.)

There are actually a lot of great natural alternatives to spray foam these days, with more in development. So I decided to just share a few of my current favorites.

• Blown-In Cellulose Insulation

  • R-value: 3.5–3.7

Made from recycled paper products, natural cellulose insulation is both sustainable and effective—and it keeps waste paper out of landfills. It can be blown into wall cavities, and provides excellent thermal performance.

As it’s blown in, it fills gaps in nooks and crannies, minimizing air leaks. It’s also treated with non-toxic borates, so it reduces the risk of fires. Just be sure you’re working with a skilled installer to prevent moisture retention.

• Softwood Chip Insulation from TimberHP

  • R-value: 3.7

Pioneering companies like TimberHP are doing some truly impressive things with wood fibers! For example, their TimberBatt is made from leftover softwood chips from sustainably harvested forests. It’s a carbon-storing, renewable, sound-dampening natural insulation. 

They also make high-performing blown-in wood fiber insulation (also from leftover softwood chips). TimberHP treats their products with borate to make them more resistant to fire, pests, and moisture.

• Hempwool Insulation by Hempitecture

  • R-value: 3.7

Hemp is a carbon-capturing, soil-regenerating crop that requires minimal resources to grow. The Natural Building community is taking note! 

Made by Hempitecture, Hempwool is made with 90% plant fibers, and contains no toxic ingredients (even the fire retardants and biocides are nontoxic). Hemp is “hygrothermal,” which means it helps control humidity without losing efficiency. It has excellent insulating properties, and is able to keep rooms cool longer than some other methods. 

Hempitecture is also coming out with a new natural product called Plant Panels, which I’m super excited about! Along with having insulation in structural cavities (walls and attics), most buildings are wrapped in exterior insulation to control dew points and minimize heat transfer. Plant Panels are a promising, sustainable replacement for toxic versions!

Can’t Avoid Spray Foam? Closed-Cell vs Open-Cell

I understand that windows and doors are particularly vulnerable areas. In some cases, I’m not opposed to using low VOC spray foam for windows and doors—but I try to keep their use as minimal as possible (only using spray foam to fill cracks or plug holes).

If you really can’t avoid spray foam, there are two types to choose from.

Closed-cell spray foam has a higher R-value per inch—usually around 6 to7. It’s also great at blocking moisture. But there’s a big trade-off in that it has a high carbon footprint. Closed-cell spray foam uses more materials, and has a higher global warming potential. While it might save you money (at least, in the short term!), it has a higher environmental impact.

Open-cell spray foam has a lower R-value of 3.5 to 4.5. You might need more of it to get the same insulation power. But it’s easier on the planet. It uses fewer raw materials and has a lower carbon footprint. It also has its perks—like being more breathable and letting moisture escape.

Choosing Your Green Insulation Products

I like to consider the type of insulation in the late stages of my design process, before I actually start the build. I want a sense of “mise en place,” knowing what materials I’m going to use, and making sure they’re available when and where I need them. That way, we’re not stalled during our build while we wait for supplies to come in. 

Here are a few tips to choosing a sustainable alternative to spray foam insulation:

• Consider your climate: What’s the average temperature in your region, and in your local microclimate? What about the annual highs and lows? Do you live in a humid area? How much insulation is recommended for your area?

• Choose an air barrier: You want a barrier that’s air-tight, yet vapor permeable. That means that air can’t blow through it, but the barrier can absorb and release moisture. (Think of it like a piece of paper.) You want that absorbent quality to help regulate humidity.

• Choose your insulation material: What material would best suit your climate and your build? How does it react to moisture and humidity? How flammable is it? What is the production process like (is it nontoxic)? How long will it last in your home? Does it expand and contract? 

• What’s your budget? If you feel at sea trying to budget for natural building materials, this up-to-date Sustainable Materials Price Sheet can help you feel confident as you move forward. It’s a comprehensive guide to all the materials you need (including natural insulation), current pricing, and where you can buy. It’s a $10 solution to staying on budget while planning your green home. Work smarter, not harder!

I know that at one point, spray foam must have seemed new and innovative. 

But resilient building is about long-term solutions. Our homes should be safe for us and safe for the earth—even after we’re done living in them. If we decide to deconstruct a building and give it back to the earth, it should biodegrade without poisoning our planet. 

By insulating our homes naturally, we can build structures that are not only energy-efficient but also healthier and more environmentally friendly.