23 Sep 2019

Ahead of the curve


If you’re looking for an eco-build holiday let, as a prospective builder or visitor, this couldn’t really tick many more boxes. High-tech passive house, Bumble Barn, is named with the bee shaped body of the building in mind.


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The curved design of this spectacular three-bedroom holiday cottage also mimics the beautiful rolling countryside of the AONB Kent Downs surrounding it. A north-westerly facing fully glazed end wall invites visitors to lose themselves in stunning sunsets and later, in the vast night skies sprinkled with stars. This future focused building is perfectly placed in a peaceful, secluded hamlet along the old Roman road between coastal Hythe and medieval Canterbury.

Built for two passionate countryside advocates, Malcolm and Lewana Castle, Bumble Barn is the creation of Oxfordshire-based modular eco-builders, Green Unit. Designed around Passivhaus principles, these curved buildings use natural, low impact materials, a stunning living green roof, smart air quality sensors, infra-red underfloor heating and minimal carbon impact. Called a ‘Green Unit ARC’, it was designed and manufactured offsite in modular sections in Culham, Oxfordshire and delivered to Great Field Farm virtually complete.

And the really interesting part for holiday cottage investors? It’s available to book through Original Cottages for between £910 to £1300 a week. With bookings rolling in, and an 8-10% return on investment predicted, the owners are thrilled they bit the bullet and built.

Eco-builders Malcolm and Lewana Castle first project managed their own home build, Great Field Farm, on a 45-acre patch of family-owned land in Stelling Minnis, Kent, more than 30 years ago. They’ve been building sustainably ever since. We spoke to Malcolm and Lewana to find out more.

Where did your inspiration to build and live passively come from?

Lewana: The joy of nature has saved me many times. We want to preserve the beauty of the countryside for generations, and we like to share our love of learning about nature. We’re just living like our frugal parents, but using technology. As a child we grew berries, composted and had chickens. My father was an electrician and had dimmer switches long before they were standard. He also built his own house with triple glazed windows to save energy. He was well ahead of his time.

What have you discovered about eco self-building?

“When we built our own home, Great Field Farm, with a heat recovery system 30 years ago, the planners thought we were crazy and would need vents. But gradually it is becoming more normal. Around 12 years ago we built a holiday barn using ground source heat pumps we knew were being used in Canada and Sweden. Again, builders and plumbers didn’t believe it would work, but they do, beautifully.

We want people to know that self-building can be reasonable, and it can be green. You don’t have to do it all yourself. Most of the build can be done off-site. We do like to introduce people to our way of life, and to share our knowledge of self-building in an ecologically conscious way. People don’t always think about how they can cut costs, but they can, and save the planet, too.

What’s the most rewarding part of house building and letting holiday cottages?

Malcolm: Building accomodation we’re proud of brings us both great pleasure. We enjoy explaining green technologies and how passive houses work. We like to think our enthusiasm for this way of life is infectious – after all, our guests return again and again!

What are the building’s eco-credentials?

Malcolm: Bumble Barn couldn’t have a ground source heat pump due to its location, so solar panels provide the small amount of energy it needs. Bumble Barn has a living sedum roof, high grade sheep’s wool insulation in the walls, ceilings and floors, a heat exchange system, infra-red underfloor heating, and smart sensors to regulate pollen, CO2 levels, ventilation, heating and lighting. It used to be that eco-friendly buildings were thought of as low-tech. Now we’re using technology to massively reduce the carbon impact of both creating buildings and living in them.

What makes Bumble Barn special?

Lewana: Being inside Bumble Barn makes you feel wrapped, cosy. It has a low profile from the outside, so it doesn’t intrude on the landscape. We fell in love with the concept and its unique curved design. We just had to find somewhere to put it. The land is beautifully placed with fantastic views and rolling countryside all around.

What do you pride yourself on offering your holiday guests?

Lewana: We’re pleased to offer our visitors the peace and freedom of outdoor space, combined with the warmth and comfort of living in a luxury house. It’s the best of both worlds for people who want to go on holiday sustainably. We have 45 acres of arable farmland, paddocks and pretty gardens to explore, and guests are welcome to spot deer, hares, pheasants, birds and butterflies on a stroll around the arable field’s perimeter nature strip. We’re perfectly located for countryside, coastal and city experiences with Canterbury and Hythe in striking distance.

Why did you go into holiday lettings?

Lewana: While I was at home raising two little boys, I realised I had to make a living alongside this. It was quite by chance. I was looking for someone to ride our two ponies and through this, I met a local B&B owner who suggested I could also offer B&B. She sent me her overflow guests, and in return, I taught her daughters to ride. The business grew naturally from there. Malcolm is great at DIY, which helped in those early days!

What are your top tips for achieving a high-end, eco-friendly finish?

Lewana: We’ve chosen Fakro triple glazing units, underfloor infra-red heating, sheep’s wool insulation, a living sedum roof, Western Red Cedar cladding, and composite bamboo flooring. Electricity is supplied by our existing 50kW solar panel array.

All our internal doors and wardrobes are oak and we used local suppliers for our British made Harrison beds and Parker Knoll sofas. The kitchen units are from Wickes. For the bathroom we sourced mosaic tiles from ebay and wall and floor tiles from Topps Tiles. Malcolm restored the dining table and coffee table – they had been sitting unloved in a barn for many years.

Why did you want the building to be created off-site?

Lewana: We liked the idea that it could be built under cover in the winter and delivered practically complete. This meant disruption to our other holiday guests was minimal.

How much did it cost and what return on investment do you expect?

Lewana: The build costs £270,000 plus VAT. As it is classed as a commercial building, we can claim the VAT back. We’re expecting an 8-10% return on investment per annum.

How long did it take?

Malcolm: The off-site build started in November 2018 and the building was delivered to site in April 2019. We think that’s a pretty impressive turnaround.

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