Sustainability has been one of the most basic issues for nearly every industry across the globe for quite some time now. And, the construction sector is certainly no exception. Today’s construction sector accounts for nearly 40% of energy consumption in developed countries. Moreover, cooling and heating of buildings amount to nearly 60% of energy use in modern-day structures.
Undoubtedly, the figures are appalling and need to be brought down considerably to counteract the effects of climate change. Switching to a renewable building material is what seems to be a viable option. When the world is busy developing more and more technology-driven sustainable materials, choosing something natural and organic that has been in use for centuries does make a lot of sense.
Yes, we are talking about hemp. Owing to its health and medicinal benefits, the plant has already become the apple of the eyes of the global health community. And, now its recognition as a sustainable building material is simply adding to its increasingly-growing popularity.
Before we try to understand how capable hemp is in bringing about a sea change in the construction arena, let’s first briefly explore its history.
History of Hemp as a Construction Material
Both health and construction-specific use of hemp has been long known to mankind. The history of hemp as a building material traces its roots back to the early 1st century. Here are a few prominent examples:
A study showed that hemp plaster was used on the floors, walls, and ceilings across the 34 Ellora Caves –a UNESCO World Heritage Site in Maharashtra, India. The earliest caves at the site were built between 600 and 730 CE.
Hemp mortar was discovered in bridge abutments of Merovingian Bridges in France that was built between 500 and 751 CE.
The Roman Colosseum or Flavian Amphitheatre, whose history dates back to 80 CE, had a rigging made with Hemp ropes that functioned as a sunshade for the audience. These sunscreen awnings at the Roman Colosseum, known as Velarium, were made out of hemp, flax, and cotton.
Parts of Hemp Used in Construction
It is no hidden fact that hemp has considerable potential to replace synthetic, petroleum-based or high embodied-energy products with sustainable high-performance materials that are eco-friendly and have less carbon footprint. The three major parts of the hemp plant used in construction are as follows:
- Woody inner core – for hempcrete
- Outer fibrous skin – hemp fiber insulation
- hemp seed oil – wood finish and deck stain
Now, let’s find some applications of the hemp parts above as in the construction sector.
Sustainable Building Materials Out of Hemp
Easy to grow and process, hemp finds a variety of applications in the construction industry. Here are some buildings materials that utilize some part or other of hemp.
It is a simple blend of hurd from industrial hemp, a lime-containing binder, and water. Hemp hurd or shiv is the inner section of the hemp plant’s stem. The hurd is chopped down to the size of around 6-25 mm to be used in making hempcrete. Owing to its high silica content, it binds well with lime.
The ratio in which all the three components are combined differs from application to application. However, in terms of weight, the general ratio is 1.5:1.5:1.5 for hurd, binder, and water, respectively for the bulk of applications.
The dry constituents are thoroughly mixed so that the lime covers all of the hemp hurd. After that, water is added. Once the mix is ready, it is then put into moulds or formwork and packed down. The degree to which the mix is compacted is decided on the basis of the density of hempcrete required for a specific application. Although the formwork is removed in a few hours, the mix can take nearly a month to completely dry and set up. This mainly depends on the thickness of the moulded hempcrete.
The dried mix is light but strong enough to be used in the construction of residential buildings. Hempcrete comes with myriad advantages, a few of which are mentioned below:
- Act as an excellent insulator
- It breathes thus, helps regulate moisture
- Gets stronger with time
- Absorbs carbon dioxide (CO2) during the curing process
- Naturally resistant to moulds, pests, and termites
- Safe to be handled
- Sound-proofing properties
- A less-embodied-energy product
- Less allergenic
- Its hygroscopic nature helps maintain low levels of humidity indoors
An interesting aspect of hempcrete’s carbon-sequestering quality is that it continues to sequester carbon long after its application. This happens because a lime-based binder keeps absorbing carbon from the air while petrifying the hurd.
However, amid all the advantages, hempcrete too has one downside – it lacks load-bearing capabilities and is used within a frame, usually made of wood. Another challenge could be its higher overall price due to additional import costs in those places, where hemp cultivation is illegal.
Having said that, the durability of a hempcrete wall is simply matchless – to the point that its life is not measured in decades, but centuries!
2. Hemp-Based Particleboard or Chipboard
Particleboard made using a mix of hemp and other fibers like flax are lighter but stronger, more durable and more resistant to moisture than their customary counterparts.
The materials in common chipboards are usually bound together using formaldehyde-containing glues that emit gas throughout the life of the product. Thankfully, such adhesives can’t be used with hemp. This means, the hemp-based clipboards are free of formaldehyde, which is thought to be a carcinogen.
Hemp-based particleboards also contribute to forest conservation. Since standard chipboards are made using wood waste, in the event of its low supply, trees are often cut down to solely fulfill the high demand of particleboards.
Presently, hemp-based particleboards aren’t widely available. Also, its manufacturing is pricier in comparison to its conventional counterparts. However, in view of the fact that more and more companies are now showing interest in this product, it is expected to become a widely available and affordable product soon.
3. Hemp-Based Insulation
Insulations made from hemp fibers comes in different forms, such as rolls, batts and solid panels. In place of unsafe chemicals, these batts make use of a small amount of polyethylene or polypropylene to bind hemp. Surprisingly, the R-value of hemp batts is similar to that of conventional insulation products of the same thickness.
Unlike other products, hemp insulation helps check moisture, never rots and is resistant to pests. It is safer to handle as it doesn’t require using protective gear; often needed while laying down conventional batts. Wearing a mask is though suggested during the laying process to avoid inhaling dust particles.
Hemp-based insulation products also have superb sound-absorbing properties and high thermal resistance. The best part is that its thermal resistance efficiency never gets compromised despite its high moisture-absorbing capabilities.
4. Hemp-Based Plaster or Render
Hemp plaster is similar to hempcrete with the only difference that its layer is kept thinner than hempcrete during application. It is applied to walls to add an extra layer of insulation and improve their sound-deadening properties.
This product can truly withstand the test of time. A prominent example is Ellora Caves, where hemp plaster has been protecting it from external elements for over 1,500 years.
5. Hemp Oil-based Wood Finish and Deck Stain
Hemp seeds are cold-pressed and processed to develop a coating, which is easy to apply, appealing and durable. Test results have shown that hemp-oil based deck stain can surpass top-notch commercial products when it comes to offering resistance against weathering. It also has very low levels of hazardous volatile organic compounds (VOCs). These make it an excellent alternative to petroleum-based synthetic polymer coatings.
Given the advantages of hemp-based products over conventional construction materials, it surely has the potential to transform the construction sector. Be it about eco-friendliness or functionality, hemp plainly outshines what some parts of our homes are currently built of.
Hemp’s illegal status in some regions and high production costs is presently a hurdle to its widespread availability. Nevertheless, as the world is turning to more and more sustainable products, hemp is likely to dominate the construction scene in the near future.