Building a sustainable house of hemp
Thursday, 28 May 2015
I've fallen in love with the idea of building a home from hemp. I recently visited Shepherds Ground Farm and Village here in the Hunter Valley while some of the members were learning how to build a wall using hemp fibre. The sustainable attributes and beauty of hemp masonry has me eager to learn more about this construction technique.
Industrial hemp is a hardy and fast-growing crop that is easy to grow organically – requiring no herbicides or pesticides.
Klara Marosszeky, managing director of The Australian Hemp Masonry Company, tells me that growing hemp is an "incredibly effective way of sequestering carbon and restoring farmland". Hemp absorbs carbon from the atmosphere as it grows and building with hemp locks the carbon up.
Growing hemp has a net positive impact on the soil. "Hemp grows to four to five metres tall in just a few months and drops its leaves to the ground, adding nutrients and carbon to the soil," Klara said.
The hemp that the Shepherds Ground homes will be built from is being grown at nearby Dungog by a recently established hemp growers’ group. An old timber mill in Dungog has been converted into a hemp processing facility.
Hemp masonry, also called hempcrete, is made using hemp "hurd" – the woody material found in the centre of the hemp stalk. "The mill in Dungog has been without power since the flood" Klara said. "But once their power is restored, the mill will extract our hurd from the already harvested hemp."
The hemp hurd is mixed with a lime binder, sand and water and then packed into a framed wall that is temporarily clad in formwork.
The process is surprisingly simple and quick.
I watched as the workshop participants mixed the raw ingredients in a large mixer and pressed it into the formwork.
Their wall was half finished by the end of day one.
Shepherds Ground member Angela Rath with a hemp masonry wall that she helped to build.
Klara tells me that the ease of building with hemp is one of its main appeals. The hemp mix is lightweight and easy to handle.
Member Karon Lindner is looking forward to living in her hemp home. "I love the beautiful natural texture of hemp walls," she said. Karon also likes that hemp is so easy to build with that she will be able to help the builders construct her home.
Unlike most building products that come with a carbon cost, hemp masonry has a very low embodied energy and can be used to build carbon negative homes.
Not only does the hemp absorb carbon while it is growing, the hemp masonry continues to absorb carbon dioxide from the atmosphere as it slowly cures.
Hemp homes are also highly energy efficient. Hemp masonry is highly insulative and, despite being lightweight, behaves similar to materials with high thermal mass. The breathable walls also manage humidity efficiently and provide excellent indoor air quality.
Hemp buildings are also fireproof and very durable. The lime-based binder coats the hemp making it highly fire resistant. The combined hemp and lime petrifies over time, making the masonry harder and stronger as it ages.
And if you should ever want to demolish a hemp home (which I imagine is highly unlikely given their beauty and performance), hemp masonry is entirely biodegradable. Simply break it up and plough it under the ground, rather than truck it to landfill.
I'm looking forward to watching the hemp village at Shepherds Ground grow.
You can check out this hemp wall at Shepherds Ground Village and Farm's first open day Saturday, June 6. Details here.
Originally published in the Newcastle Herald Monday 25th May 2015.