House of hemp more than a dream
Photo by Mike Moores
Sean Manners will harness the unique qualities of hemp for his environmentally friendly house at Westbury.
By Sharon Webb
SEAN AND Mandy and Jade the Jack Russell Terrier are getting a new house in Westbury. But not just any house. It’s an environmentally friendly house. Okay, that’s not so unusual these days. Lots of people are into solar passive, double glazing and water tanks. They’re up to their ears in insulation and can talk Tesla batteries till the cows come home. Mandy and Sean Manners have all that. And more. Because their house is made of hemp. According to Sean it’s about future planning, longevity, and having a house that doesn’t cost a fortune in heating, cooling and maintenance. And it’s about minimalism and simplicity. It’s built on an insulated slab and the floors will be polished concrete. No carpets because they’re an unnecessary extra layer. ‘We’ve kept it simpler,’ Sean said. ‘We’ve done away with floor joists, the cover for the joists, the floorboards, the carpet.’ Simpler doesn’t mean basic though. Mandy wanted a pantry, easy undercover access to the house, an easy-care environment and the kitchen designed so that she could socialise while cooking. All of that is happening.
There is a sunroom for the solar passive aspect of the design. It heats up during sunny hours and can be shut off when it’s cold. The home’s footprint is angled on the block to make the most of sunlight and large eaves will keep it shaded in summer. The hemp? ‘I looked at mud brick and straw bale but hemp seemed to be a logical choice. It seemed achievable,’ Sean said. ‘When Klara Marosszeky, the managing director of the Australian Hemp Masonry Company came to Tasmania, we asked her to run a small workshop. As I started exploring the idea it made a lot of sense as a sustainable building material.’ Sean’s building material, hemp hurd, he explained, is the inner part of the industrial hemp plant’s stem. Industrial hemp is used for fibre and oil. The hurd is waste – but it has unique properties. ‘It can hold 14 times its own weight in moisture,’ Sean said. ‘It naturally allows moisture, say from a bathroom, to pass through the wall and out of the house.’
There’s more. Hemp is fire-resistant. And hemp is carbon negative. Most buildings are carbon positive. Hemp hurd used for building is mixed with a lime binder, sand and water to make hempcrete. Some say it’s harder than concrete. Finance-challenged owner-builders need stacks of friends to help tamp this mixture into the formwork because it’s time-intensive. But the lime in the mix gradually takes in carbon dioxide and carbonates over time. ‘Over the life of the building it will take in more carbon than we used to build the house.’ Sean said. ‘Hemp stores a lot of carbon when it’s grown, then this lime process adds more. ‘It helps in a small way to combat climate change.’ And hemp is an excellent insulator so Sean is hoping he won’t need to heat the house. A small pellet heater is on stand-by because it is Tasmania after all. The hemp for Sean and Mandy’s house comes from NSW. While Tasmania grows more hemp than anywhere else in Australia, we don’t use enough hurd to make it worthwhile for our growers to invest in the machinery to process it.
There are just two burning questions for Sean to answer. When will we be able to see the finished home? ‘It’s almost to lock-up stage now and I’m aiming to finish it in August. People will be able to see it during Sustainable Homes Day in September.’ More importantly, anyone who enjoyed Sean and Mandy’s inaugural pizza party at their previous home will be wanting to know whether they were able to move the Sean-built adobe pizza oven to the new house.
No is the answer. But he will build another one. In August Sean and Mandy and Jade the dog will move themselves and their Hyundai Ioniq electric car into their hemp house. Quiet house, quiet car, quiet neighbourhood. And all environmentally friendly. Sean and Mandy Manners’ house was designed by architect Will Goodsir and built by Andreas McMahon who have worked together on other hemp buildings.
