Hemp can be used in building homes in many ways. Building with hemp is very different than building with conventional construction methods.

Hempcrete can be tamped into board-formed walls, used as premade bricks, sprayed into cavities, or formed into precast panels.

It acts as insulation and as an interior and/or exterior surface, though it is not load-bearing – you still need a wood frame.

This article will review all the ways that hemp can be used to build a healthy home.

Before we look at the building methods closer, let’s look at what goes into hempcrete. 

What is Hempcrete Made of

1. Hemp hurd

The first ingredient of hempcrete is the aggregate, called the ‘hurd’. Hurd is the woody core of the hemp plant that remains after the plant has been stripped and the fiber sold for rope or textiles. 

The hurd is like the inside of a twig, after the bark has been stripped off, just less dense and with a hollow core. The woody core is dried and then chopped up; it looks a lot like wood mulch. 

Hemp is an organic material – meaning, it is carbon-based, just like wood (and can be mold food, just like wood). In fact, it contains more cellulose than wood does (hemp has 65-70% cellulose and wood has 40%). 

Quality is not consistent from supplier to supplier, so make sure you are buying good quality hurd before committing to a large purchase.

A good place to buy hemp hurd in the US is through Hempitecture in Idaho. 

2. Lime Binder

The lime binder contains calcium carbonate (lime) and compounds which allow it to harden – either soluble silica, alumina oxide or ferric oxide. When a lime binder can harden with the addition of water, this is called hydraulic lime. 

Hydraulic lime is readily available in the UK and France but is difficult to find in North America and often has to be imported. 

There are some binders that are produced in the US. One place to buy lime binder in the US is also through Hempitecture.

Do your research on binders before choosing one. There are binders out there that have caused mold problems where there shouldn’t have been any due to added ingredients in the binder. 

3. Water

When water is added to the hydraulic lime binder, it causes a chemical reaction (hot!) which makes it possible for it to harden once dried. 

4. Air

It feels funny to list air as an ingredient, but it’s one of the most important parts of hempcrete! 

When dried, there are many air pockets in hempcrete – both between the pieces of hemp and inside each piece of hemp. 

Air is what makes hemp a good insulator (air is the most important part of any insulation) and humidity regulator.

Put them together! 

When hemp hurd is mixed with the lime binder and water, it dries into a hard solid mass. 

Before it dries, you sprinkle it into framed molds that surround the building’s wood framing. It is then tamped down to compress it a bit, and left to dry. 

The drying time is important (between 4-8 weeks). If you don’t allow it to dry enough before removing the form work and plastering, there could be big problems (mold, staining, crumbling).

Mixing hemp and lime together: https://www.instagram.com/p/Bsn2G21hMxn/?utm_source=ig_embed&utm_campaign=loading

Building with Hempcrete: How it is Used

Hempcrete can take the place of insulation, drywall, and siding in a new wall. 

It is not a 1 to 1 replacement, though; Hempcrete can’t just be substituted for fiberglass insulation (or cellulose, etc.). Using hempcrete requires a different plan and approach compared to conventional building. 

Besides being a totally different type of material and insulation, hempcrete has a different insulation value than fiberglass or cellulose, and so it will require thicker walls.

As Insulation

This is a cross-section of a hempcrete wall – the hempcrete encapsulates the wood framing.

Hempcrete’s most important function is as insulation. The amount of insulation you require will determine how thick your wall will have to be. 

The insulation requirement (R-value requirement) depends on your local codes. The colder the climate, the thicker the wall will have to be.

Hempcrete’s R-Value is usually listed as ranging from 2-3 per inch. But some companies have claimed it can be as high as 4.8 per inch.

Photo courtesy of Hempitecture. 

As Siding (Exterior Skin)

This is the exterior wall of a hempcrete tiny house before plastering.

The outside of hempcrete can be plastered, similar to the interior. This can create more moisture risks if not done precisely or maintained properly. 

This might not be advisable in certain climates. Please find a professional to discuss what the best exterior options are for your climate.

Photo courtesy of Hempitecture.

As Interior Wall Face (Interior Skin)

This is an interior hempcrete lime-plastered wall.

Drywall is not needed when building with hempcrete. The typical interior finish is a lime render (plaster) that is applied directly to the dried hempcrete. This allows the wall to stay vapor permeable.

Anything that you add to the wall must be vapor permeable, inside and out. 

Photo courtesy of Hempitecture.

Note! 

Hempcrete is not concrete. Unlike what the name suggests, hempcrete is not made from concrete and it does not contain concrete. Even though hempcrete dries and hardens, hempcrete is not structural or load-bearing – it can’t hold up the weight of the roof. It must always be used in combination with a wood frame (or other framing material). 

Reasons to consider hempcrete

• Hemp has a unique cellular structure that allows it to absorb and adsorb water better than other plant-based fibers. This gives it an edge in moisture management over other plant-based materials.
• The use of a lime binder makes glues and other high VOC materials unnecessary for the wall components. 
• It can help with maintaining healthy indoor air quality.
• It is a fast-growing crop, so multiple harvests can be grown in one year (it is a weed, after all).
• Hempcrete generally has very good (but not excellent) insulation value. 
• It is very fire-resistant.
• We know all of the ingredients in it.
• It is vapor permeable, i.e. “breathable”- if moisture gets in, it can get out.
• It is carbon dioxide sequestering.

Building with Hempcrete, Various Forms

1. Poured, or Formed Hempcrete

With formed (or poured) hempcrete walls, the finished walls are hardened hempcrete usually plastered with a lime render.

How it works

The hemp, lime binder, and water are mixed together on-site. 

Temporary wood framing aka form work (similar to when concrete is poured) is placed surrounding the structural wood frame. 

The hempcrete mix is then “poured” into place inside the wood forms and then tamped down to create a thick wall. The wood forms are left there for several weeks until the hempcrete is dried. 

Hempcrete creates a solid wall. There is no need for an interior wallboard, like drywall, just a nice lime plaster. 

The thickness of the wall will depend on how much insulation is required by code in your location, or how much insulation you want. 

Depending on location, the exterior can also just be plastered, but this should be discussed with a building science-literate professional who is familiar with your climate zone. 

Photo of hemp in exterior forms: https://www.instagram.com/p/Bsa_xkVjMMi/?utm_source=ig_embed&utm_campaign=loading

Benefits of a solid hempcrete wall

• A good amount of thermal mass (heavy, thick walls) makes temperatures and humidity more even.
• Using a single material means no seams and gaps like in traditional, wood-framed houses.
• A homogeneous material makes moisture and temp management more consistent.
• A heavyweight, formable material means less need for taping or specific air-sealing layers.
• Building with a homogeneous material means there’s no abrupt shift in temperatures (i.e. at the sheathing), minimizing the chance of condensation.
• Consistent vapor openness due to single material (hempcrete) makes it easier for the wall to “breathe” and dry.
• Hempcrete works with moisture, humidity, and temperature like an experienced dance partner; conventional construction relies on keeping them away by using increasingly complex layers of barriers, insulation, boards, and tapes.

Drawbacks of a solid hempcrete wall

• It could give you false reassurance – it still requires extensive planning and precision to avoid mold.
• Industrial hemp is grown with large amounts of fertilizers.
• If not planned, mixed, and detailed correctly, it can become moldy .
• The lime dust can be hazardous – one of the hydraulic set lime binders includes a “may cause cancer” warning.
• Using a framing material (i.e. wood) is still necessary. 
• There are many unknowns about how it will perform in US climates.
• Contractors and laborers may be inexperienced with hempcrete.
• You will be an “early adopter”.

2. Pre-Cast Hempcrete Blocks

In order to make hempcrete thick to have enough insulation value, you can use precast hempcrete blocks on one side of the exterior wall.

The opposite side will be framed with temporary forms and be poured with hempcrete to fill the cavities and encapsulate the wood framing.

Hempcrete blocks are not load-bearing, so they will still need to be used with a wood frame. 

There is one company in Canada that is making a load-bearing block. They have not responded to my request for more information about the block. Their block is not approved for load-bearing use in the US. 

Components

Most hempcrete blocks have the same ingredients as poured walls – hemp hurd, lime binder, and water.

However, there are some that have different binders, or use a finer ground hemp, and these can cause problems. 

Always make sure you know what is in the block before committing to anything. 

Like in the picture below, the hempcrete blocks will be placed on one side of the wood-framed wall. 

A build with hemp blocks in progress: https://www.instagram.com/p/B3WirPkntVr/?utm_source=ig_embed&utm_campaign=loading

Benefits of using hempcrete block

Same as benefits for poured hempcrete, plus:

• They are pre-dried, so you can begin applying interior plaster weeks earlier than with poured hempcrete. 
• Faster install time.

Drawbacks of hempcrete blocks

Same as poured hempcrete, plus:

• The cost is higher due to the labor required to cast and dry the blocks off-site.

A layer of hemp blocks complete: https://www.instagram.com/p/B3pkZnKn8uy/?utm_source=ig_embed&utm_campaign=loading

3. Sprayed-In Hempcrete

This type of hempcrete is mixed on-site, like poured hempcrete, but applied by spraying rather pouring into a form. It’s a similar process to wet-applied dense-packed cellulose or spray foam.

There must be a surface to spray against, like a hempcrete block layer or plywood.

This is a video of the whole preparation and spraying process. 

Components

Same as in poured hempcrete: hemp hurd, lime binder, water.

How it works

Mixed on-site, like poured hempcrete, but applied by spraying vertically rather than pouring into a form. 

According to Alex Sparrow, who owns UK Hempcrete and is the author of The Hempcrete Book, in the UK it is common to use sprayed hempcrete when renovating old stone houses. The stones have uneven surfaces and spraying allows the hempcrete to fill in the gaps and valleys. 

Spraying in hempcrete: https://www.instagram.com/p/Bz_LQRRBYW7/?utm_source=ig_embed&utm_campaign=loading

Benefits of sprayed-in hempcrete

Same as poured-in hempcrete.

Drawbacks of using sprayed-in hempcrete

Same as poured concrete, plus the possible compression of the hempcrete, resulting in lower insulation values.

4. Hempcrete Prefab Panels

Some companies are beginning to produce prefab wood frame hempcrete panels. These panels combine structural wood framing with hempcrete.

Components

The ingredients in prefab panels are usually the same as hempcrete. But, like blocks, it could vary from company to company, so make sure to find out what the binder is before committing to anything. 

How it works

The panels are framed with wood. They are sometimes referred to as “cassettes”. When using prefab panels, the wood framing is not encapsulated with hempcrete. 

Panels will require more care for air sealing, etc. due to the wood joints. There is also more potential for thermal bridging and condensation. 

Uses for prefab hempcrete panels would be similar to any prefab panel. Wall sections are made off-site and transported to the lot for installation. They could be used in place of hempcrete blocks, with poured or sprayed hempcrete on the opposite site.

A video showing hemp precast panels: https://www.instagram.com/p/Bz8amlcBfr-/?utm_source=ig_embed&utm_campaign=loading

Benefits of using prefab hempcrete panels

• Possible faster install time.
• Faster dry time.
• Less on-site prep.

Drawbacks of using prefab panels

• More detailing, similar to a traditional construction wall, because wood frame is not encapsulated in hempcrete.
• More expensive.
• Less oversight for how the wall is being made.
• More potential for problems with the wood.
• It makes interior finishes more tricky (lime plaster over studs?).

Precast panels: https://www.instagram.com/p/ttjdPmhKt4/?utm_source=ig_embed&utm_campaign=loading

5. Hemp Insulation Batts

Hemp insulation is not hempcrete but I thought I would briefly mention it here. It is not mixed with a lime binder that encapsulates the hemp hurd and hardens it.

It is hemp fibers, usually with some synthetic fibers mixed in, made into batts and used in walls just like fiberglass, mineral wool, and other batt insulation types.

My post on insulation mentions this in more detail.

Is Hempcrete Mold Resistant?

Plain hemp can grow mold in the right conditions, but hempcrete is a little different.

 

Hemp is made of cellulose (it has even more than wood!) and mold likes cellulose. If you put plain wet hemp in a plastic bag and seal it, it will get moldy. 

Hempcrete has less risk for mold. This is because the hemp in hempcrete is mixed with a lime binder that makes it possible for the hempcrete to harden. 

Lime is what gives hempcrete its mold-resistant property. Lime is alkaline (high pH). Mold, in general, doesn’t like alkaline environments. When the lime binder is mixed in and coats the hemp pieces, it essentially creates an inorganic, alkaline buffer that mold cannot survive in.

However, one study I read found that mold was still able to grow, even in the presence of lime binder, when the hempcrete wall was exposed to heavy rain. 

A lot depends on using the right binder, mixing it correctly, making sure anything put on the walls is vapor-permeable, and avoiding bulk water (rain, roof-run off, etc.).

When a hempcrete house is properly planned and correctly built, the chances of mold growing are likely less with hempcrete than with traditional building materials. 

Do your research on binders before choosing one. There are binders out there that have caused mold problems where there shouldn’t have been any. 

If you want to avoid mold in your future healthy house, proper planning for moisture management (weather and vapor) are essential. 

Please find a qualified architect or building science professional to create a plan for your new healthy home.

What climates are safe for building with hempcrete?

It seems that hempcrete can be used in almost any climate, with the right details and correct installation. 

There are many hempcrete houses in the rainy UK, as well as institutional buildings and multi-family complexes. 

In North American, there are hempcrete buildings in coastal North Carolina to snowy Idaho and cold, wet Canada. 

Since hempcrete is an insulation, it should be just as safe as something like blown-in cellulose. The details will change depending on the climate, however – humid, dry, rainy, cold, warm, etc. 

It might be necessary to protect the exterior wall with large overhanging eaves, or sheathing combined with a rain screen (gap) and siding. 

This is where an experienced architect can help you determine the details that are necessary for your location to avoid mold and rot.

Is Hempcrete Cost Effective?

• The cost appears to be 10-30% more than typical wood construction.
  • Much of it has to be imported (and it can be difficult to source, depending on where you live).
  • It takes a long time to dry which can slow down the build.
• The cost depends on the method you use.
  • A double stud wall is more expensive (double cost).
• There are very few experienced architects or builders.
• Blocks and precast panels tend to be more expensive because they need to be cast individually unlike a whole wall that can be cast as one.

Related post: on more natural building wall systems to consider.

Where to Learn More About Hempcrete

Helpful books:

• The Hempcrete Book: Designing and building with hemp-lime by William Stanwix and Alex Sparrow
• Essential Hempcrete Construction: The complete step-by-step guide by Chris Magwood

Helpful videos:

• Alex Sparrow speaking at Hempfest
• Introduction to Natural Hempcrete Construction Options

Trainings:

• US Hemp Building Summit – annual 
• Endeavor Centre – Canada
• UK Hempcrete

Products:

• Hempitecture – hempcrete samples, hemp hurd, blocks, hempwool, binder, and tools/machinery
• Hemp Eco Systems
• Tradical Hemcrete
• Tradical Hembuild – Pre-cast wall panels
• Sativa Building Systems – insulated panels
• CannaGrove HempBoard
• Just BioFiber – blocks 
• NaturHemp insulation panel
• AcoustiHemp semi-rigid acoustic panel
• NaturFelt Hemp Wool floor underlayment

Design / Build

USA

• Hempitecture – Idaho
• Homeland Hempcrete – North Dakota
• New Frameworks – Vermont

Europe

• UK Hempcrete

Corinne Segura is a Building Biologist Practitioner with 7 years of experience helping others create healthy homes.

There are so many excellent choices for non-toxic, healthy, green insulation, there should be one to fit everyone’s needs.

Look out for Greenwashing

There are many new options that claim to be “green” “soy-based” or are formaldehyde-free – this does not mean that they are VOC-free or safe. Look very closely at what’s in it. Also, flame retardants and mildewcides are not counted as VOCs.

Green Certified?

On top of that, certifications are not that useful: almost every insulation now qualifies as GreenGuard Gold, which for sensitive folks is not enough information.

The post includes the best of green non-toxic insulation and includes a cost comparison as of 2021.

I recommend all of the products here, some products have affiliate programs and some do not. Upon purchase, I earn a small commission through affiliate links at no extra cost to you.

For assistance with choosing the best insulation for your needs, sensitivities, and budget, you can contact me for a one-on-one consult. 

Options Used in Wood Framed Houses

1. Fiberglass Insulation

Fiberglass is the most common insulation used in standard stick-framed houses in Canada and the US. For this reason, I am starting here. It’s not actually my top pick in the batts category.

You can use it between wooden studs of a house, between floor joists, and in the attic. It is used in many trailers, but I don’t recommend that.

This option has improved dramatically in recent years, and the following brands are now extremely low in VOCs.

Formaldehyde-Free Fiberglass Brands:

1. Knauf EcoBatt is recommended by many extremely sensitive folks who could not tolerate polystyrene, cotton, or wool. They are formaldehyde-free and their declare label lists all ingredients down to 100 ppm.

2. Owens Corning Ecotouch fiberglass insulation has GreenGuard GreenGuard Gold certification. The binder is formaldehyde-free and “made from widely available plant materials”, according to the company. All ingredients except the pink dye are listed. The patent can be found here.

3. Certainteed Fiberglass insulation is also made with a plant-based binder.

4. Johns Manville Fiberglass insulation is GreenGuard Gold and uses a formaldehyde-free acrylic binder. A patent by the company that is likely related to this product can be found here.

What are BioBinders in Fiberglass Insulation?

We don’t know much about what bio binders actually are, but by looking at this patent you can tell that they look mostly safe. However, it’s hard to zero in on what it is.

There are some preservatives in there, and when they use a biobased binder it looks like they are adding a biocide. (According to patents the acrylic binders might also use biocides, but which type is unknown).

Are there Flame Retardants in Fiberglass?

Fiberglass insulation is made with boron but I don’t see any other flame retardant added, especially in the batts that do not have paper backing, and in the spray in type.

Neither Declare labels nor the companies’ patents suggest flame retardants. Pharos also does not list flame retardants as a component.

Blown-In Fiberglass

Blown-in fiberglass that I have looked at recently contains borates, soda ash, lime, siloxanes/silicates/silane, mineral oil, and an unknown anti-static additive.

Owens Corning unbonded loose-fill and Knauf Jetstream Ultra look similar. A client reported a “strong smell” from JM Climate Pro Fiberglass blown-in, but I don’t see the ingredients for that one, so I cannot compare it to the other two.

• R-Value
  • 3.5 inches is R-11-R-15.
• Cost USD (2020)
  • Knaff Ecobatt is 0.49/sq ft and you can buy it at Home Depot or through your contractor.

2. Mineral Wool Insulation

Mineral wool is my top choice for batt insulation. It is in widespread use by builders who build green or high-quality homes and it is the most obvious alternative to fiberglass. It is also easy to source.

• The batts can be used between wood studs anywhere in the house.
• It’s very good at staying in place with compression fitting, so it fits well between framing.
• It fits and holds up well in ceiling joists.
• It can be used in an attic if detailed really well and if you don’t do well with any of the blown-in options.
• It can be used on basements walls.

Non-Toxic Mineral Wool Brands

1. Rockwool (formerly Roxul) is the most common and accessible mineral wool insulation.

They have a newer version, called AFB evo, that does not contain formaldehyde. The binder is an undisclosed polymer (a plastic, likely acrylic). It also contains mineral oil. It’s much harder to source than their standard batts.

The standard Rockwool ComfortBatt does contain phenol-formaldehyde which will cure completely and quite quickly if it’s not already cured by the time it gets to you.

Rockwool ComfortBatt is the type for perimeter exterior walls, Safe N Sound, their soundproofing version is for interior walls, and ComfortBoard is exterior insulation (outside of the sheathing).

All three contain the same binders/additives: <3% phenol-formaldehyde, <1% starch, and <0.2% mineral oil source.

You could try both options (the regular and AFB evo), but there are few situations in which the regular Rockwool does not work for someone after airing it out for a short time.

2. Thermafiber by Owens Corning is a brand that has a regular phenol-formaldehyde line and a formaldehyde-free line (you will see the letters FF), the latter usually has to be special ordered through a store. They also have a blown-in option as well.

3. American Rockwool is a brand that is harder to source (in 2020 they stalled production). The company claims no chemical additives or binders, and that would be a bonus for the extremely sensitive. They also have a blown-in option.

Other Info

An easy way to cut through mineral wool is with an electric carving knife.

This insulation has good soundproofing qualities. The Safe N Sound version can be used on interior walls for soundproofing between rooms.

The fibers can cause a contact allergy if you are not using gloves, but the insulation itself is hypoallergenic for most people.

• R-Value
  • 3.5 inches is R-15.
• Cost USD (2020) 
  • $0.95/ sq ft for Rockwool (Comfortbatt, 3.5 inch)
• Where to Buy
  • You can find Rockwool and Thermafiber at hardware stores across the US and Canada, or through your contractor.

3. Wool Batt (and Blow-In) Insulation

Wool batting might be the next insulation type to consider if you want a non-fiberglass option and you have ruled out mineral wool.

It can be used between wood-framed walls and in the attic floor. It’s more expensive than fiberglass and mineral wool above.

Top Brands of Wool Insulation

1. Havelock Wool has no synthetic fibers and no binders. It’s only wool and boric acid. They provide a Declare Label for all of their ingredients. This is the purest of the wool options (and really the most natural insulation all around).

It’s definitely a favorite in the environmentally sensitive community. You can buy it online which makes it the most accessible wool brand.

2. Oregon Shepard adds boric acid, sodium pentaborate dehydrate, and a proprietary component that includes a natural protein, last I checked with them.

3. Black Mountain NatuWool which is 95% wool and 5% polyester binder and is treated with borax.

Blown-in Wool Insulation

The purest option here will be the blow-in wool insulation.

Some extremely sensitive folks have done well with Oregon Shepard blow-in and another extremely sensitive person did well with Havelock loose-fill. I tested Havelock and found that it did have a noticeable wooly smell, though others have barely noticed it.

The natural oils of the wool have an odor that may not work for some sensitive people, although it is not an additive or chemical smell.

While none of them claim organic certification, wool is one of the purest options.

As for borax/boric acid, I’m mostly concerned about inhalation, ingestion, and absorption through touching eyes and mouth. I’m not very concerned about it once it’s behind the wall.

• R-Value
  • Wool in batts has R-13.7 in 3.5 inches
    Blow in dense-pack R-value: can be 15.3 in 3.5 inches
• Cost USD (2020)
  • Havelock Loose Fill is $1.97/sq ft
    Havelock Batts is $1.62/sq ft
• Where to Buy
  • Buy through local green building supply shops or buy Havelock online.

4. Recycled Cotton Batt

Ultratouch Insulation is what my builder used in my chemical-free tiny home. If you rule out fiberglass, mineral wool, and real wool, this would be something else to consider.

It used to be made from new denim scraps, but they have moved to recycled denim now. It does contain boric and ammonium sulfate and an olefin binding fiber (similar to rayon).

You have to test it for your own sensitivities. I became more sensitive to fabric treatments after I moved into my house (and I had the type made from new scraps).

I would not use this insulation again due to its poor ability to hold itself tight in the walls, the potential for mold if it gets wet, and the slight odor I picked up.

It can be used between wood-framed walls though it does not hold itself up well in ceilings/between floor joists, especially compared to mineral wool. I personally would not use it in a basement.

• Other Info
  • Wear an N95 mask while cutting and installing as it does get extremely dusty when working with it.
• R-Value 
  • For the 3.5” thickness, you get an R-Value of 13
• Cost USD (2020) 
  • $0.79/sq ft
• Where to Buy
  • This had to be special ordered when I built my house. Now, you can buy it at Lowes and Home Depot.

5. Hemp Insulation

Hemp insulation is the newest alternative insulation in the North American market. It’s been used for much longer in Europe.

I think it is very promising. It’s harder to source and more expensive than some of the other options in this category, but it could be really great for someone who wants something natural and who hasn’t done well with the other options above.

Brands

1. Thermo-Hemp out of Europe was one of the first brands.

2. NatuHemp Semi-Rigid panels are available in the UK and Canada. Canadian NatuHemp, which can be shipped throughout Canada and the US, is made of 88% hemp fiber and 12% polyester fiber, with no chemical binders and no off-gassing (they claim).

3. HempWool is 92% wool and 8% polyester. It’s available through their website and ships within the US (not to Canada).

Companies have been coming and going out of business rapidly in the hemp insulation industry.

Ask them what they add to it, apart from hemp: alternate fibers, binders, flame retardants, and if it’s organic. And always test a sample first!

• R-Value
  • It is R-13 for 3.5 inches
• Cost USD (2020)
  • NatuHemp is $1.80/sq ft
    Sunstrand batt is $1/sq ft
• Where to Buy
  • Contact the companies on where to source it.

Blown-In Insulation

1. Cellulose

Recycled cellulose is an option often slated for those with chemical sensitivity. It is a blown-in insulation made with recycled newspaper that contains a fire repellent like boric acid.

Newspapers are made with “soy-based” inks but they still contain many other chemicals in the inks apart from soy, and there are additional additives in the insulation, usually mineral oil.

Dense-packed cellulose is often used in Passive House design, which has great attention to details around moisture management and green healthy materials.

It is used in both walls and attics.

Safe Brands of Cellulose Insulation

1. Greenfiber brand from Lowes and Home Depot is 85% recycled newspaper. It contains boric acid, sodium poly borate, sodium tetraborate pentahydrate, amylopectin, and mineral oil.

2. Ecocell makes batts that are a mix of cellulose and cotton. It also contains PET plastic, very small amounts of boric acid, as well as sodium poly borate, and ammonium sulfate. You can find this insulation without ammonium sulfate – that may be special order. This used to be sold at Home Depot but now it’s not clear where to source it.

3. Weathershield brand by Rona in Canada.

• R-Value 
  • 13.3 for 3.5 inches
• Cost USD (2020)
  • $0.32/sq ft

2. AirKrete Cementitious Insulation

https://www.instagram.com/p/B5S7DjoBMSk/

AirKrete is a cementitious blown-in insulation that claims to be VOC-free. It has passed the “sleep next to it test” of many chemically sensitive people.

The company, however, has declined to participate in the industry-standard VOC test as well as the proper R-value test, so there is some doubt around this product’s claims.

We don’t know what the undisclosed 2% of this product’s ingredients are, but many with severe chemical sensitivities have chosen to go with this option and have done well with it.

Because it is a foam, it will get into all the cracks and crevices and therefore give you a higher “real life” R-Value than the batts.

Some people have reported shrinking, crumbling, and trouble drying. Here is the source for the concerns.

Paula Baker-Laport continues to recommend this insulation, so I’m assuming that many are still doing well with it.

It can be used in walls and roofs. (Consult with an architect when designing an unvented roof).

Non-organic options like AirKrete are more likely to be hypoallergenic.

• R-Value
  • R-13 for 3.5 inches
• Cost USD
  • Around $2.25/sq ft including installation costs
• Where to Source
  • You would have to check to see if you have a certified installer in your area before proceeding.

3. Real Wool, Mineral Wool, and Fiberglass Blown-In

These three insulation types can be blown in as well. Fiberglass (pictured) is the most common blown-in insulation, followed by cellulose.

Mineral wool and real wool blown-in are less common but are healthier choices.

Brand names can be found in those respective sections above.

Exterior Insulation for Houses 

1. Styrofoam/Rigid Foam

i. Polyisocyanurate “Polyiso” Foam Board Insulation

Polyiso is one of the insulation types that is used on the exterior side of sheathing.

Typical current blowing agents for polyiso are CO2 and pentane. There is some “thermal drift”, meaning the blowing agents offgas over time. The offgassing is extremely minimal.

This is going to become a very common exterior insulation as building codes move towards requiring exterior insulation.

It can be used in trailers and metal structures as well. It’s not to be used under slabs.

Flame retardants are a bigger concern than trace pentane. The most common flame retardant is TCPP. It’s best to look for brands that don’t use a halogenated flame retardant like TCPP. Newer and safer flame retardants are non-halogenated phosphorus-based.

Though the foil does block the FR, the edges are unsealed and it will never be perfect.

Healthy Brands of Polyiso Foam Insulation

1. Johns Manville Foil Faced Polyiso has been the most popular brand among those who are sensitive, but they have discontinued Energy 3E, which was the one made without TCPP (all they have said is that it is phosphorus-based and is non-halogenated).

2. GAF polyiso EnergyGuard-NH uses a halogen-free flame retardant (which is phosphorus-based, like the Energy 3E FR was). “Unlike TCPP, the flame retardant becomes part of the polymer backbone of the insulation—so there is no free flame retardant that can leach out”, according to GAF’s director of sustainability Martin Grohman. “TCPP, by contrast, is not chemically bonded to the polyiso polymer, so it can more readily escape.” Source

3. ZIP System R-Sheathing is the Huber Zip OSB sheathing, polyiso, and weather-resistant barrier all in one. Though you can use the above two brands as exterior insulation on the outside of the plywood or OSB, “ZIP-R”, as this type is normally called, is integrated with the sheathing, with the polyiso on the interior side.

• R-Value 
  • Technically it’s R-6/ inch but it’s really about R-5.6/inch over its lifespan because it loses R-Value over time. It also loses R-value the colder it gets.
• Cost by R-Value (R6)
  • R-6 is $0.60 / sq ft

ii. Extruded Polystyrene (XPS)

XPS (extruded polystyrene) is another common exterior insulation outbound of the sheathing. It is also used on exterior concrete basement walls, underneath the slab, and in trailers.

XPS, like polyiso, has some “thermal drift” i.e. some very slow offgassing of the blowing agents over time.

“Over a long period of time (50 to 75 years), the blowing agent slowly diffuses through the thickness of the foam” (source).

Typical blowing agents for XPS are CFC-12, HCFC-142b, and HFC-134a, but they change their formulas over time. HFC-134a was eliminated from extruded polystyrene on January 1, 2021.

XPS insulation was treated with the flame retardant hexabromocyclododecane (HBCD) until recently. The two main brands, Dow Styrofoam (Lowes) and Owens Corning Foamular (Home Depot) no longer contain HBCD.

Most are now using a butadiene styrene brominated copolymer as the flame retardant (Source). DOW lists a brominated flame retardant (FR122P) in some of their XPS.

How Concerning are These Flame Retardants in Rigid Foam?

Flame retardants are sometimes considered non-volatile and sometimes semi-volatile. They leach out in dust form as opposed to gas. If they become dust borne in the house, the main route of exposure is hand to mouth, though you can also inhale them.

My post on Flame Retardants goes into more detail.

• R-Value
  • R-5/inch
• Cost by R-Value
  • R-5 is 0.60/ sq ft

2. Mineral Wool Board 

The other common and easy-to-source exterior insulation used in the US and Canada is Rockwool, in board form.

The Rockwool Comfortboards will be used more and more as many codes across the US shift to requiring exterior insulation.

Foam and Rockwool will be the two main exterior insulation types to consider since they will be familiar to builders and easy to source.

The boards can also be used on interior basement walls. They are also being used under the slab, as the only alternative to foam insulation there.

• R-Value 
  • R-4/inch
• Cost by R-Value (R6)
  • R-6 is $1. 24 sq ft

3. Cork

Thermacork insulation, unlike cork flooring, does not contain adhesives. It is held together by compressing it with heat which releases a natural binder in the cork.

The cork does give off a smoky smell that dissipates with time, as well as the natural odor of cork.

This is a newer product in North America and is more expensive than the more conventional options.

If you can afford it, it is my top pick for non-toxic exterior insulation due to a lack of additives and flame retardants.

It can be used as exterior insulation or even the facade of a house which serves the purpose of siding, insulation, and noise reduction.

See this post as an example or cork used as the facade.

• R-Value
  • R-4/inch
• Cost by R-Value (R8)
  • R-8 (doesn’t come in R-6) it’s $4.93/sq ft for the insulation type (rougher than the facade)
    R-8 in the facade grade, which covers your exterior insulation and your siding in one, is 10.77/sq ft
• Where to Buy
  • You can buy this through green building supply stores.

4. Wood Fiberboard Insulation

Wood fiberboard is often used in High Performance/Passive House designs as exterior insulation. It can be used closer to the interior as well.

One popular brand in North America is Gutex. It is 95% wood (spruce/fir, post-industrial, recycled and new wood), 4% polyurethane, and about 1% paraffin. The total VOC level is 187 μg/m3.

• R-Value
  • R-3.7/inch
• Cost
  • R 5.8 is $1.81/sq ft
• Where to Source
  • You can buy this through 475.

Insulation Typically Used in Trailers, RVs, and Vans

1. Rigid Foam

EPS (Expanded Polystyrene aka Styrofoam)

EPS (expanded polystyrene) is often used in trailers and can be referred to as “block foam” by the companies.

It can also be used as exterior insulation, insulation over concrete basement walls on the interior, and under the slab. Though you are far more likely to see the XPS type of styrofoam under a slab.

Blowing Agents

EPS usually is made with pentane as a blowing agent, the final product has trace amounts of pentane which dissipates rather quickly and completely. Some butane can also be used as a blowing agent.

Sometimes the only blowing agent is carbon dioxide (based on DOW xnergy Declare label).

Zero-VOC

EPS, despite the name (polystyrene), does not offgas styrene under normal conditions.

It is considered 0-VOC (and pentane and styrene are not exempt from the VOC testing).

What about Styrene?

The concerns over polystyrene (styrofoam) and styrene comes from the following a) chemicals released during the manufacturing of the product b) the product is very toxic if you burn it and c) the styrene can leach if you drink beverages especially hot or acidic beverages out of styrofoam cups.

This is a very old product with a long track record. Here are a couple of links to back up the claims.

In the form of insulation, I would consider this product to be non-toxic, zero-VOC, odorless, and stable, with the only risk being the flame retardants.

Flame Retardants

EPS used to be treated with hexabromocyclododecane (HBCD), but luckily it no longer is. Polymeric FR (a copolymer of polystyrene and brominated polybutadiene) is now the most common FR.

The foil faces on these insulations block the flame retardants. However, the foil and plastic-backed versions can have some offgassing odor. Some EPS is not backed with anything.

EPS used in packaging and cups does not contain a flame retardant and people have sometimes been able to source this type of foam for small structures.

If using EPS in a living space I would recommend borate treated foam to prevent ants from tunneling in.

R-14 for 3.4 inches EPS.

2. Reflectix and Prodex Insulation

Reflectix is a bubble foil made of aluminum over polyethylene bubble wrap. It is flexible, very thin, and claims to have a very high R-value. The thicker version claims R-21 (which is higher than 5 inches of wool).

These claims are disputed by Green Building Advisor and the Government of Canada. The former states that the 3/8th-inch foil has an R-value of only 1 (the same as a single pane of glass).

This would hardly be useful anywhere unless it is in a curved trailer, RV, or vehicle where all other options have been ruled out. Sometimes it’s just used to insulate windows, which can be a great help.

Prodex is another similar material – foil and polyethylene-based – that also has a disputed R-value.

Many similar brands can be found easily on Amazon or Home Depot.

3. Aerogel Insulation

Aerogel is a fairly new product – unusual, extremely expensive, and harder to source.

The term itself can refer to a variety of materials from the original silica translucent product to polymer-based products that may include the addition of fibers.

The original Aerogel insulation was developed by NASA.

Aspen Aerogel collaborated with NASA to make their polymer enhanced aerogel combined with fibers.

Some companies are selling insulation online that they claim is Aerogel. I would look closely at what’s really in it. Look for proper studies on the R-Value of it.

They claim an extremely high R-value of R-10 to R-30 per inch.

This may be ideal for small, round, and difficult to insulate places, if you can source it.

4. Thinsulate Insulation

3M Thinsulate (SM600) is an insulation used in vans, other vehicles, and RVs.

It is made of polyethylene terephthalate (a type of polyester) and polypropylene fibers which will be tolerable for most people. The backing is polypropylene.

One percent or less of the additives are proprietary and therefore unlisted. The health rating is 0 which is good.

What I don’t love about using this product in vehicles is that the insulation itself is vapor permeable and it is attached to the walls with 3M 90 Spray (GreenGuard certified, not GreenGuard Gold, not reported to be very tolerable by many chemically sensitive people).

You may find this insulation tolerable and it may be a good product for a tiny house or structure.

You can buy it on Amazon and Ebay.

R-value

5.2 for the 1.65 inch

NB. I have seen similar but more unusual insulation made from polyethylene and polyester for homes in batts. (It is more popular in some countries outside of North America.) It may be tolerable depending on what is added to it.

5. Vacuum Insulation Panels 

Vacuum Insulation Panels have the highest insulation value of any of the insulation materials.

These Panasonic panels have an R-Value of R-60 per inch. They were used in the latest Leaf House design (tiny house). This could allow you to build a tiny house for almost any climate. Though this introduces a tricky metallic vapor barrier which needs to be carefully thought out.

The foil vacuum pack will block any VOCs from migrating through, but your moisture management system would have to be planned carefully here.

These won’t work in most houses. You might consider them in some trailers or metal framed homes.

They are very pricey and harder to source than almost all of the other options.

6. Non-Toxic Spray Foam Insulation

Spray foam that is used to fill cavities of walls is two-part polyurethane. Some of it may have soy added, but it’s still mostly polyurethane foam.

This insulation has to be mixed perfectly, under the right conditions (there are many), and applied correctly. When looking for a good spray foam you are looking for an excellent installer (the best one you can find) and not a specific brand.

The companies have claimed that it is no-VOC, or close to that once cured, but many individual tests and many individual noses of those sensitive have shown otherwise.

I know moderately sensitive folks who have looked at many houses with spray foam and been able to pick up the odor for two years.

And that’s when it’s done right. When it’s done wrong it’s a massive disaster that can end in a lawsuit against the company, plus an expensive imperfect removal of all the foam.

If you are extremely sensitive you would lose the whole house if this goes wrong, as the VOCs will soak up into other materials. This has happened to two of my clients.

Brands:

Icynene and Demilic are both 2-part polyurethane spray foam.

Whether they have soy or castor oils in them is insignificant in my overall view.

Icynene OC No Mix is still a 2-part polyurethane foam and although it appears to mix in the gun, the installation still has to meet all of the other parameters.

One part polyurethane:

One part polyurethane, which is the canned stuff discussed below, is much easier to tolerate, it’s used in small quantities, and it doesn’t have the same challenges and risks as the 2-part foam.

Insulating Around Windows and Doors – Non-Toxic Options

Spray foam is often used around windows and doors. HandiFoam is GreenGuard Gold and will be tolerable for many folks after curing. In Canada, the best source is Organic Lifestyle.

I find this spray foam to be odorless once cured.

Other brands like Great Stuff, which you can find anywhere, seem very similar to me, if not the same.

Great Stuff does contain a flame retardant in some of its lines and Handi-Foam has declined to answer whether it contains a flame retardant or not.

Instead of using spray foam around windows and doors you can fill in the gaps with Backer Rod and seal with non-toxic caulk if needed.

I have a post on caulking if you need to test multiple brands.

Corinne Segura is a Building Biologist Practitioner with 7 years of experience helping others create healthy homes.

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