Written By: Sumedha Chandra Sekhar
Before the 1900s, Hemp was one of the most significant crops amongst humankind. However, now it is most widely recognized as nothing but a plant that "gets one high." Considered to be one of the first plants ever spun into usable textile fibers more than 10,000 years ago, hemp is now finally moving away from its century-old reputation as we find more industrial uses for it every day. Some of the more famous uses are food, paper, clothing, beauty, and biofuel. But one of the biggest untapped uses of hemp is construction material, also called Hempcrete.
Hempcrete is said to be the most sustainable building material and a better alternative to concrete and steel. Mixing Hemps woody fibers with lime produces a natural light concrete that preserves thermal mass and is highly insulating. It is fire, pest, and mold resistant with good acoustics, low humidity and effective at regulating temperature. The material is carbon negative, meaning its construction consumes more carbon than it produces thus the carbon footprint is almost negative, as carbon is literally locked away inside the material. The only drawback? Growing this green building materials can land you in jail since the plant's farming is highly controlled in most countries and requires a license.
Typically planted in the months of March and May in the northern climate, Hemp plants take only four months to grow from seed to harvest. They are then cut by hand and let too dry for a few days before bundled up and dumped into vats of water to swell the stalks. The dried fibers are mixed with lime, and the result is a lightweight installation material and when fully cured, the hempcrete blocks float in water!
More like drywall than concrete, it is not used as a structural element or for the foundation as it is an insulation which needs to breathe. It should not be used at ground level either as it would lose its resistance to mold or rot. Lime plaster coating is also necessary to be applied to anything that touches hempcrete otherwise the lime can harden and thus lose its ability to absorb and release water. Most often, it's mixed on-site and poured directly into a frame.
In many climates, a 12-foot hempcrete wall can help maintain an approximate 60-degrees indoor temperature year-around without cooling or heating systems which can overall lower the environmental footprint dramatically lower when compared to traditional construction.
Hempcrete was first discovered in France in the 6th Century, so why isn't it more popular you may ask?
A popular material used in Europe for decades, a New York Times article paints us the European-hemp picture, "Hundreds of buildings now use hempcrete, including a seven-story office tower in France, a Marks and Spencer department store in the United Kingdom, and even a home built by Prince Charles." Almost any house that can be built with brick and steel can be built
with hempcrete and a structural frame.