Last Updated: May 8, 2023
With winter setting in, improving your home's insulation is one of the best ways to reduce your carbon footprint and save money on your monthly energy bills. Air leaks around windows, doors, and foundations also drain your home's thermal performance, with up to 50 percent of heat loss due to faulty and non-tight building envelopes. You can read a complete Rise guide on how to avoid home heat loss here. Suppose you know for sure that certain areas of your home need an upgrade in insulation. In that case, spray foam insulation might be an option worth considering. Below, we offer a complete rundown on the pros and cons of this increasingly popular insulation alternative. We also provide a few recommendations to help homeowners find the highest performance and most environmentally friendly spray foam to boost their home's energy efficiency and thermal performance.
Spray foam insulation, also known as spray polyurethane foam (SPF), is gradually becoming a popular and widely accepted insulation alternative. While fiberglass and other "batt-types" of insulation used to be the primary option for home insulation, installation could be challenging for some homes and hard-to-reach areas. Spray foam insulation was developed in the 1940s by the US military during World War II. At that time, they applied this high-efficiency insulation to airplanes. Three decades later, in the 1970s, this insulation alternative started to be used in homes. However, it wasn't until recent years when spray foam insulation became sufficiently cost-effective to become a significant player in the insulation industry.
Almost all spray foam insulation is made from polyurethane foam, which is the same material that goes into soft furniture like couches, chairs, and Memory Foam mattresses. When properly applied, spray foam insulation offers excellent thermal insulation for homes due to its high R-value (how insulation capacity is measured). Spray foam insulation can be easily applied to hard-to-reach areas such as the corners of attics or low crawl spaces around your foundation. So, this insulation alternative can also minimize air infiltration by sealing your home's building envelope.
Spray insulation comes in both open-cell and closed-cell varieties.
There are two main types of spray foam insulation available for insulation your home's walls, ceilings, attic, and foundation. Open-cell polyurethane foam insulation, also known as half-pound foam, is generally the lighter option. Open-cell foam is not sufficiently dense to act as a water, moisture, or vapor barrier. Because of this, it cannot be used in areas where exposure to moisture or vapor is likely (i.e., bathrooms, foundations, etc.). However, open-cell polyurethane foam insulation can limit air leakage while still providing high-R value insulation in dry areas like walls and attics.
Closed-cell polyurethane foam, also known as two-pound foam, is much denser and offers protection against both air and moisture. Because of its ability to repel moisture or vapor, this type of foam insulation is most often used as an insulator for foundations and anywhere in your home where a vapor barrier is needed.
Both open-cell and closed-cell polyurethane foam insulation can be effective insulators in different areas of the home. However, most builders prefer closed-cell foam insulation due to its slightly higher R-value and moisture barrier properties. Closed-cell foam insulation has an average R-value of around R-6 per inch. This R-value is significantly higher than most other insulation types, including fiberglass batts, cellulose insulation, and open-cell foam. In comparison, open-cell foam generally has an R-value of just 3.5 per inch. Though this is comparable to other types of insulation, closed-cell polyurethane foam is undeniably the better insulator.
For many homes, this means that you can reduce the thickness of insulation without sacrificing your home's energy efficiency and thermal performance. Of course, the extra insulating value and the added protection as a moisture barrier comes with a higher price tag. Closed-cell polyurethane foam insulation commonly costs twice as much as open-cell spray foam insulation. However, prices have been falling in recent years.
The main drawback of both open-cell and closed-cell polyurethane foams is their environmental footprint.
Though foam insulation can reduce the amount of energy (and thus carbon emissions) needed to heat and cool your home, the blowing agents included in these foam products can also have an enormously higher global warming potentials (GWP).
The tiny bubbles or air pockets within polyurethane foam is what gives this insulation alternative its high R-values. However, to create these bubbles or air pockets, the foam requires the use of a blowing agent during insulation.
The blowing agents most commonly used in polyurethane spray foams are hydrofluorocarbons (HFCs). A study by the Climate & Clean Air Coalition found that HFCs are powerful greenhouse gases. They can be hundreds or even thousands of times more potent than carbon dioxide (CO2) in their contribution to climate change per unit of mass. They also note that a study showed that 0.1°C of warming could be avoided by 2050 if low-GWP alternatives replace high-GWP HFCs.
We usually think that the insulation we use in our homes can help to lower our home's carbon emissions by reducing energy for heating and cooling. However, HFCs' high global warming potential might essentially negate any reduction in emissions that come with improved home energy efficiency.
For comparison's sake, carbon dioxide (CO2) has a global warming potential of 1. Methane gas (CH4) has a much higher GWP, between 28 and 36, over one hundred years. However, the hydrofluorocarbons (HFCs) used as a blowing agent in your spray foam insulation have a GWP of over 3,400. This fact essentially means that the HFCs used as blowing agents are 3,400 times more potent at speeding up climate change than carbon dioxide on a per kilo basis. Each kilogram of HFCs released into the atmosphere is the same as sending up 3.4 tons of CO2!
Many companies are beginning to address the high global warming potential of the blowing agents used in spray foam products, fortunately. Many spray foam insulators today include blowing agents that have a significantly lower global warming potential. The US Environmental Protection Agency estimates that global HFC consumption in building and construction foams globally accounted for about 38 million metric tons of CO2 equivalent in 2010. Certainly, transitioning to low-GWP foam products is an essential part of the green building transition. To support this, some building certification programs, like Passive House, have banned the use of HFC-containing spray foam products.
Several brands of spray foam now offer lower GWP levels, with more becoming available every year. Some of these low GWP products include:
Insulthane is a leading spray foam insulation that uses a blowing agent known as Solstice®. It has a GWP of just 1 (the same as carbon dioxide), thus offering a 99.9 percent reduction than other foam alternatives that continue to use HFC blowing agents.
HandiFoam High Density offers an impressive 6.5 R-value per inch. It also uses HFO blowing agents, which drastically reduces the GWP of the product.
Gaco spray foam insulation is also a high-performance closed-cell foam insulator that uses a low GWP blowing agent. Gaco's spray foam insulation also contains polyols derived from naturally renewable oils, post-consumer recycled plastics, and pre-consumer recycled materials.
Also, look out for BASF Walltite CM01 and Genyk Boreal Nature, both of which are low GWP spray foam insulation products. In general, make sure to look for spray foam insulators that use HFOs instead of HFCs as primary blowing agents.
The targeted thickness for your spray foam insulation will largely depend on the climate where you live. In general, spray foam applications for home insulation are installed in 3/4-inch to 3-inch-thick lifts. In places with mild temperatures, home builders will generally spray two inches in walls and three inches in roofs to meet the energy code requirements of R-13 and R-19, respectively. The more extreme the temperature variations, the more insulation is recommended. For instance, it is not uncommon for Passive Houses in Canada wall assemblies insulated to R-40.
Spray foam insulation can be used throughout the home, including walls, roof, attic, and foundations. However, as we explained above, you will need to use closed-cell polyurethane spray foam in areas where moisture or vapor is an issue. Closed-cell insulation is necessary for insulating a foundation.
Spray foam insulation is exceptionally durable and it is said that it can last for up to 80 years. The main issue or problem arises when open-cell polyurethane foam is installed in areas where moisture or vapor damage can occur. To avoid this problem, opting for the slightly more expensive closed-cell foam insulation can guarantee improved durability. However, it is important to note that as with all newer technologies, we don't yet know how they will perform over the long term.
In general, closed-cell polyurethane foam costs between $1.00 and $1.50 per board foot. Open-cell polyurethane foam is slightly less expensive at $0.60 to $1.00 per board foot. Opting for spray foam insulators that use low GWP blowing agents such as HFOs might increase the total installation cost by 10 to 15 percent. However, this high-performance insulation alternative's improved performance could also result in energy savings of between 10 to 15 percent at the same time.
Professional technicians should install spray foam insulation. It's recommended that home occupants vacate the home during installation. Spray foam insulation will off-gas large amounts of volatile organic compounds (VOCs) during both the actual spraying and the curing process. Homeowners should stay away from the home until the curing process finishes, generally in 1-3 days, until the house has been properly ventilated.
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.