Hemp has been proven to be a great resource used in producing everything from clothes to rope to diapers to sunscreen to milk. Industrial hemp is non-intoxicating (under 0.3% THC), and can be grown as a renewable material.
Hemp was illegal to grow in the United States as part of the 1937 Marijuana Tax Act (regulating the sale of all cannabis) and the 1970 Controlled Substances Act (classified all cannabis forms as a Schedule 1 drug). The 2014 U.S. Farm Bill allowed states to pass their legislation regarding the growing of industrial hemp.
This journey has paved the way for hemp to be used in a growing number of construction applications. One aspect that has been proven to be the most beneficial thus far is the use of hemp in insulation.
What is Hemp Insulation
Hemp insulation is a composite material but one that is very eco-friendly. Instead of consisting of 51% plant fibers and 49% plastics and chemicals, hemp insulation contains as much as 92% hemp and about 8% polyester fibers. Non-toxic bonding agents and fire treatment make up the rest of the composite.
Hemp insulation is most often available to be purchased in batts. The batts are thick (3.5″ to 5.5″) and compressible, so they look more like something found in a soundproofed recording studio than the thinner fiberglass batts most homeowners are familiar with.
Hemp insulation is viewed as an alternative to fiberglass and foam – one that has less impact on the environment during manufacturing. Since hemp is a natural plant product, the insulation offers organic advantages when installed and disregarded.
What are the Ecological Benefits of Hemp Insulation
Hemp insulation has only been produced in North America since roughly 2018, so it's considered a very new addition to the market. There's legitimate reasons to believe that hemp insulation could bypass fiberglass to be the industry leader sooner rather than later.
Not only is hemp a plant, it's also what's considered a break-or cover-crop. This means that hemp is planted to increase soil health by shading out weeds, which reduces the need for herbicides. Hemp has different nutritional needs than wheat, which helps improve the overall structure of the soil by adding nitrates and potassium.
Hemp has a long taproot that grows deep into the Earth, loosening compacted soil and providing access to a better water table. Plus, it grows fast (like a ‘weed'). Hemp doesn't need a lot of room to operate either as one acre of hemp can yield roughly 700 pounds of grain. It has a quick turnaround of as few as 70 days from plant to harvest.
Hemp is a crop, so right of the bat is a sustainable product that can be renewed. Hemp does not require insecticides or pesticides to protect it from insects in the field, and it is also a plant that consumes very little water.
At the end of life, hemp insulation can be recycled or ground up for compost since it is an organic material. Eco-friendly homeowners should consider the environmental impact of the manufacturing process and the reclaim methods of their building materials. The process of recycling asphalt shingles puts nearly as much strain on the environment as producing the product.
How Does Hemp Insulation Perform?
Some household products, such as bamboo floors, are very environmentally friendly but scratch easily and have a short lifespan overall. Hemp insulation, on the other hand, stacks up just as much in the performance field as it does in the ‘green' department.
Aside from R-value, one of the most significant benefits of hemp insulation is how it reacts to moisture. Hemp fibers are very breathable, so vapor travels through the insulation – which is a good thing. The hemp acts as a filter for condensation, slowly dissipating the wetness as it travels through the product. Hemp is hygroscopic, which means it absorbs condensation to help control a home's humidity.
Hemp insulation is so impervious to moisture that it can hypothetically be removed, dried, and replaced if a wall were to experience water damage from something like a pipe leak. Hemp is like a towel or sponge in terms of water exposure, whereas fiberglass is more like a cotton ball in that it's going to break apart and be a loss when wet.
Any contractor will tell you that the most significant benefit of hemp insulation is that it's much more pleasant to install than fiberglass batts or loose-fill cellulose. “Insulation day” is a miserable experience that leaves the installer itching, coughing, and generally unpleasant for hours afterward.
Hemp insulation is a dense product too, on average 3.5″ to 5.5″ thick but available up to 7.5″, which adds acoustic absorption properties. Hemp insulation comes in 4′ long batts, which will stay firm when stood up between wall studs. Rolled fiberglass or even blown-in insulation will slouch or compress over the years.
What is the R-Value of Hemp Insulation
Ultimately the main goal a homeowner wants from their insulation installation is to reduce the amount of air entering and leaving their property through the walls. The terms used for the performance of insulation are known as R-value and U-value.
R-value measures the thermal resistance of insulation. The higher this number, the better your insulation will restrict heat and chilled air loss. Hemp has an R-value of 3.5 per inch of thickness, which is about the industry standard. The ability of hemp to be compressed is where its installation becomes an advantage. A 5.5″ piece of hemp insulation can be installed between 3.5″ studs to provide an R-value of 19.25, which is more than the requirement of even the coldest zone in the United States (zone 7).
U-value measures heat transfer, and conversely from R-value, the lower on this number, the better. Hemp has an excellent U-value of .039, which is the same as roughly 8″ of fiberglass insulation installed in walls.
Hemp Insulation vs. Fiberglass Batts
Surprisingly hemp still isn't considered a standard form of insulation to most building contractors. Using hemp to insulate is relatively new, and most of the product remains imported from Canada or Europe. Contractors who were told that recycled blue jeans were the ‘insulation of the future' a few years ago are still leery of using hemp instead of other more proven materials.
There are four types of standard insulation that hemp has to stack up within the industry. The categories are loose-fill/blown, batts, foam board, and spray. Hemp insulation could be considered half batt, half foam board, and that versatility gives hemp an advantage right from the start.
Regarding batt comparisons, the most popular current material is fiberglass or mineral wool bundles held together with adhesives. Fiberglass batts have an R-Value ranging from 2.9 to 3.8. In terms of resisting heat flow, fiberglass batts and hemp offer very similar production. The u-value (heat transfer) of fiberglass batts is just .05 per six inches, though. A standard fiberglass batt is only about 3.5″ thick, so it would take roughly 8″ (or two pieces) to match hemp's u-value.
One thing to note about fiberglass batts is that it absorbs moisture without permeating it. The fiberglass material will suck up condensation and then just let it sit there, which leads to mildew growth. Therefore uncovered fiberglass batts would also need a vapor barrier installed. It's not a big deal to install a plastic sheet for a vapor barrier, but it's also just one more thing that can fail.
Hemp's most significant advantage over fiberglass batts is on the environmental side. Small shards of glass (as the name suggests) make up a majority of the fiberglass insulation. Still, other bonding agents include silica sand, limestone, soda ash, borax, aluminum, feldspar, and more. Not only are these products dangerous to inhale by sticking to your lungs, but they also increase the energy consumed in the manufacturing process.
Hemp Insulation vs. Rigid Foam Board
The other insulation product most often used besides fiberglass batts is foam board. Expanded polystyrene, or styrofoam, has an R-value of 3.6 to 6+ per inch. Foam is rigid, so it stays in place, but that also means it's more challenging to work with around outlets, pipes, and wires, which lead to air loss.
Rigid foam board is the most moisture resistant of nearly any insulation, and some products have reflective foil installed to further deter heat absorption. Once again, though, the environmental impact of manufacturing foam is much more devastating than with hemp. Foam contains chlorofluorocarbons, which contribute to ozone depletion and global warming. Some types of foam insulation, such as phenolic, are no longer manufactured because of the damage to the atmosphere.
Hemp vs. Other Insulation Types
The other two insulation categories, besides batts and foam, are loose fill and spray. Loose-fill insulation still consists of small particles of fiber and foam, among other harmful things to be inhaled when installed. Cellulose does have the most effortless installation when there isn't access to the studs (hole cut in the top of the wall and envelope filled). The R-value of cellulose is 3.2 to 3.8 per inch, but that decreases as fibers sag and compact over the years.
Spray foam or spray polyurethane foam (SPF) creates the tightest seal of any insulation when installed properly. Open-cell spray foam has an R-value of 3.7 per inch, while closed-cell can be as high as 6.5 per inch. The spray releases vapors and aerosols during installation, however, and this might be an example of a product that is too good. Homes that are sealed too tight can allow nitrogen dioxide and carbon monoxide to build up and allow moisture to accumulate like a greenhouse.
Hemp Insulation Cost Comparisons
The reason so many contractors continue to use fiberglass insulation, even though it is so annoying to install, is quite simply the cost. Fiberglass bats range from $.64 to $1.19 per square foot, whereas 3-1/2″ batts of hemp cost around $1.80 and the thicker 5.5″ pieces of material are roughly $2.40.
Rigid foam board costs $1.41 to $2.48 per square foot to install, but that's just the 1″ thick material. Open-cell spray foam ($0.44 to $0.66 per board foot) and closed cell spray foam ($1-1.50 per board foot) all have similar costs because they are estimated on volume. Ultimately hemp is right in the price range of these other popular insulation types – the only problem, for now, is finding the hemp.
Choose Hemp Insulation
Availability will be the ultimate downfall of hemp insulation for the foreseeable future. More and more manufacturers and contractors need to realize the positives that hemp can have as an insulating material to be more prevalent in the industry. Unfortunately, there are currently so many hoops to jump through right now regarding growing and cultivating hemp that many contractors are sticking with the status quo of fiberglass and foam insulation.
The good news is that the red tape is starting to become less and less stringent. More states are beginning to move forward in easing hemp farming regulations. Hopefully, that will lead to more entrepreneurs seeing the value in using hemp as a viable crop for insulation and other building processes such as hempcrete – a mixture of plant fibers, limestone, sand, and other composites.
Once the hemp building revolution does start to come to light, contractors will be thankful. As far as installation goes, hemp batts are more preferable ten out of ten times than fiberglass. When you factor in the environmental advantages hemp has over different foams, it's time for contractors and homeowners to start seeking out this alternative insulation source.