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The Next Step in 'Green' Building

Green living - taken to a 'higher' level. It seems silly that for so long (and right under our noses) Hemp has provided us with so many sustainable solutions yet most people will still automatically dismiss the wonder drug because of it's taboo (completely ridiculous made up facts) association with the 'war on drugs'. It seems however, just like sustainable living, the world is waking up and we are happy to share a story that infuses both.

The idea for GreenBuilt came about almost a decade ago after the victims of Hurricane Katrina were left without shelter, with mold-damaged homes and toxic temporary housing. A few years later, when Haiti was hit by a devastating earthquake and thousands of people were buried under collapsed concrete houses, the need to find a solution became more urgent. GreenBuilt searched for a healthy, durable, climate resilient material that could provide high-quality permanent housing as well as temporary shelter. That’s how they discovered hempcrete.

What is Hempcrete?

Hempcrete is a composite of the hurd, or shiv (the chopped up woody core) of the industrial hemp plant, and a lime-based binder. Hempcrete materials can be used as insulation, to form wall systems around a structural skeleton, or formulated into blocks, boards and panels. They can also form virtually the entire building envelope for a HempHome.

  • Insulate Along with R-30 insulation and permanent air tightness, scientists have shown that hemp-lime dampens heat transfer through the wall.

  • Modulate Hempcrete walls breathe, reducing indoor humidity in the summer and increasing it in the winter.

  • Eliminate Hempcrete is non-toxic, and it’s mold, insect and rodent resistant. As a plant-based material, it also eliminates the carbon footprint – when it’s built, and for the life of the building.

Why Hempcrete?

Hempcrete is a natural, non-toxic, renewable building material that does not contribute to global warming. It’s mold, pest and fire resistant. Its insulating properties modulate humidity and temperature.​

Whats the point?

Our Tiny House Will Protect Your Health and Help Preserve Our Planet

Our design and construction team, led by AIA award-winning architect Christina Griffin, is committed to developing HempHome: Tiny+ as a beautiful, sustainable solution for healthy buildings. Tiny+ does not require the burning of any fossil fuels even in the cold, snowy winters and hot, humid summers of the Northeast. Designed to provide superb indoor air quality, superior comfort, and unmatched resilience, it will be the first modular HempHome to meet the stringent healthy building and energy efficiency standards of The Passive House Institute and the Living Building Challenge.

In parallel to creating HempHome: Tiny+, we are developing prefab hemp-lime panel technology that will enable future HempHomes to be built quickly, inexpensively and to individual tastes. With prefab modules, people can customize their HempHomes— add a bedroom for a child or an elderly parent, set up an in-home office or workshop, live off-the-grid, or create a community dedicated to a sustainable lifestyle.


We want our supporters to be able to walk through Tiny+ and feel firsthand what they helped create. We want you to see how easy it is to construct beautiful, healthy housing. Fall 2016: Come take the tour!​

The Vision:

GreenBuilt was founded on a vision of a healthy, sustainable world that begins in our own homes, neighborhoods, farms, factories and workplaces.

GreenBuilt is fast becoming a community of entrepreneurs, activists, architects, advocates and builders dedicated to creating better buildings with Hemp.

Even though HempHome: Tiny+ is a tiny house, it’s a big step toward reducing greenhouse gas emissions and building vibrant regional economies.

Some Interesting Questions and Answers:

  • Why hemp?

For buildings that are energy efficient, environmentally friendly and non-toxic, made from natural materials and have a carbon footprint that’s less than zero, hemp provides unique advantages – its pore structure allows it to naturally regulate humidity as well as temperature.

  • What’s the difference between “Hemp” and “Marijuana”

Technically, industrial hemp and marijuana are both Cannabis Sativa. While high-THC cannabis is psychoactive and has valuable medical applications, industrial hemp is the non-psychoactive, low-THC strain of the Cannabis plant. Hemp has absolutely no use as a recreational drug, but hemp fiber’s applications range from textiles to bioplastics, hemp hurd is used as a building material or animal bedding, and hemp’s highly nutritious oilseed is used in food and personal care products.

  • What is hempcrete?

Hempcrete is a composite of the hurd, or shiv (the chopped up woody core) of the industrial hemp plant, and a lime-based binder. Hempcrete materials can be used as insulation, to form wall systems around a structural skeleton, or formulated into blocks, boards and panels. They can also form virtually the entire building envelope for a HempHome.

  • Where do hempcrete materials come from?

Industrial hemp is a fast-growing annual crop, grown around the world for fiber, hurd and oil. One acre can produce enough hurd in 14 weeks to build a 700 sq. ft. house with 8-inch thick (R-20) walls. After harvesting, the hurd is separated from the plant’s long strong outer fibers, then chopped up to be mixed with a binder to create the building material. While hemp product markets are growing rapidly in the U.S., industrial hemp is not yet widely grown here due to legal prohibitions against its cultivation. These laws are changing rapidly as states and the federal government recognize the economic value of industrial hemp. Lime is one of the world’s oldest building materials. Limestone is quarried in many sites across the U.S., and then heated in kilns to make either hydrated or hydraulic lime. Lime, which is used as the binder in hempcrete materials, is widely available in the U.S.

  • Why use hempcrete materials?

Hempcrete materials provide many advantages over other insulation and wall envelope assemblies. Hempcrete walls are simpler than most conventional wall systems. They don’t need a vapor barrier, additional sheathing, rain screens or complicated engineering to prevent moisture buildup in the walls. Vapor permeable, i.e. breathable hempcrete walls regulate indoor humidity. They allow moisture to pass through the wall instead of getting trapped in the wall cavity. Yet they are air tight and provide good thermal insulation. The lime binder provides fire and mold resistance, repels pests (insects, rodents, etc.), and makes the composite extremely durable. Hempcrete provides good racking resistance and becomes structurally stronger over time. It does not deform or crumble and so does not slump or create air gaps in the walls.

  • What is the insulating value of hempcrete?

The R-value varies with the density of the mix—the more binder, the less insulation. Generally, hempcrete formulations have R-values of around 2.5 per inch, yielding an R-30 for a 12” wall. European experience has shown that R-value is not the whole story, however. Hempcrete materials demonstrate properties of thermal mass, absorbing heat during the day and releasing it at night. This creates a more consistent temperature inside the building throughout the 24 hour period, adding to indoor comfort and reducing energy bills. And as a result of its hygroscopic properties, hemp-lime has also been shown to regulate humidity, providing indoor comfort at lower winter and higher summer temperatures than other materials. While these factors contribute to apparent occupant comfort, they do not yet enter into energy calculations.

  • I’m sensitive to chemicals and toxins. Can I use hempcrete?

Hempcrete is completely natural and non-toxic. In addition, its ability to mitigate interior moisture issues improves indoor air quality. The hygroscopic qualities of the lime binder, combined with its alkalinity (ph of 12), creates an environment that stops mold growth.

  • What are the advantages of hemp-lime over conventional insulating materials like foam and fiberglass?

Hempcrete materials are much more environmentally benign in their production. They do not require toxic chemical additives to provide fire-resistance. They are not toxic to breathe and they produce no VOCs. Installation and mixing require minimal protection—just gloves, a mask and goggles. There are no glass particulates or chemicals to inhale or to irritate the skin. Hempcrete materials do not slump or shrink like batt insulation can, causing an air gap at the top of the wall. Because the material is applied around the structural skeleton, the load-bearing frame is protected from moisture, weather, mold and pests.

The application of hempcrete is relatively low-tech and moderate-skill. With a bit of training and instruction on mixing the right proportions of hemp, lime and additives, the technique can be learned quickly.

Hempcrete mixtures are strong and add structural stability to a building. They get stronger over time as the material cures. At the same time they are lighter than other materials such as cement and drywall.

Hempcrete is carbon-negative. As a crop hemp absorbs CO2 and after becoming part of a building in a wall or ceiling the hemp-lime composite continues to absorb CO2. Because of its humidity modulation properties, hempcrete composites are extremely well suited to insulate masonry buildings. They do not create moisture build up and deterioration that often result from retrofitting with other materials.

  • How strong is hemp as a wall system?

Hempcrete is not concrete – it does not function as a structural component, and it’s much lighter and has far lower compressive and structural strength than concrete. That said, as part of a wall system (combined with structural wood or steel) it has been engineered to withstand strong earthquakes and winds up to 130 mph.

  • Does building with hemp cost more?

Building with hemp is a little different than the typical construction process, and today is likely to cost about 7-10% more. We are working to get the cost of hemp building down, so that initial costs will be on a par with other, less sustainable practices. We think this can be done by developing regional sources of raw materials, and by developing prefab processes to reduce construction time. Even though the up-front cost is higher now, over the life of the building it should still cost less than other materials, due to improved air quality, excellent thermal performance, and reduced maintenance requirements.

  • What kind of sheathing is used with hempcrete building envelopes?

Sheathing is not necessary with hempcrete walls, as hemp-lime walls can be pleasingly finished with lime renders alone, inside and out. If a sheathing layer is desired, the sheathing must be vapor permeable. Conventional drywall cannot be used. Paint finishes must also be vapor permeable, so mineral paints are the way to go.

  • Can hempcrete materials be used in all climates?

Hempcrete materials have proven comfortable and effective in places as diverse as Southern Spain (where summers are very hot and dry) and Western Canada (where winters are very cold and snowy). Hemp can be used as a building material in most areas of the U.S. and Canada. It makes most sense, however, to use hempcrete in areas that will benefit from its unique properties. In the Northeast, for example, we experience high humidity in summer and pretty extreme 24-hour temperature fluctuations in winter, spring and fall. We have issues with rodents and insects getting into our buildings and problems with moisture build-up in our walls which lead to mold and rot. We also have a large stock of older brick and stone buildings that could be effectively retrofitted with hemp-lime insulation. But almost anywhere people want healthy, non-toxic, high-performance buildings is a good place to build with hemp.

  • How long does a hempcrete building last?

Hempcrete has been in use in Europe for about 25 years, and we don’t know of a single instance in which it was properly installed and had to be replaced. A French lifecycle assessment said that hemp-lime should last well over a hundred years.

  • Will I get “high” if my hempcrete building catches on fire?

Hempcrete is actually significantly more flame resistant than the common insulated wall. Due to the flame resistant properties of hemp-lime, it is very unlikely that it will ever catch on fire. Testing in the UK shows that hemp-lime is naturally fire resistant and will resist fire up to 1,800C (cement shatters at 400C). And if it did burn, anyone wanting to get high from the smoke would be extremely disappointed. The THC levels in industrial hemp are way too low. Of course, it also wouldn’t emit toxic fumes, as flaming buildings with spray foam and other chemical insulation materials do.

  • Is it legal to build with hempcrete?

While growing industrial hemp is still illegal in most of the U.S., building with the material is not. However, until the materials are fully certified and more widely understood, the permitting process for permanent hempcrete buildings could take some time.

In closing: (From the GreenBuild)

We know that building with hemp works – it’s been growing in Europe for more than 25 years in both large and small new buildings and in retrofits across the continent. We also know that it’s a big task to make a beautiful Tiny House that reaches Passive House standards and is certified Net Zero by the Living Building Challenge. And we are well aware that getting the cost of hemp building down so that everyone can afford hemp homes is a tall task.

We believe we have the team in place to meet these challenges. Our architect Christina Griffin is an experienced Passive House professional and designer of beautiful buildings, our construction crew has built everything from boats to barns, and our advisers have years of experience working with hemp, indoor air quality and marketing.

Our biggest challenge is to get costs down so that everyone can afford hemp homes, and we are working hard to improve our building processes and techniques, create new prefab modules, and develop our regional supply chain. We see a lot of progress on the legal front – almost day by day, hemp is getting closer to being legal to grow here in the US—but we’re not there yet. Once we prove that the market is there, the government will have to lift restrictions on hemp. Our production time frame is tight, but our team is focused on building the first HempHome Tiny+ this summer.

In closing: (From Us)

An idea we can get onboard with! We wish the GreenBuild team all the success in the world and ask all our readers to please help spread the word by sharing this post - you just never know who it might reach and who's life it could change.

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