Research by the Eindhoven University of Technology showed that a greenhouse residence is less likely to overheat than a super-insulated, airtight house
A conservatory is comedy shorthand for neighbourly one-up-manship. So what would you think if someone completely encased their entire home in glass?
If the British love of all things Scandinavian continues, it may not be long before home-owners are enclosing draughty old traditional properties in bespoke greenhouses.
After all, that's what a handful of our trend-setting Swedish neighbours have been doing for several years now.
When, in 2002, Charles Sacilotto bought a wooden house on an island in the Stockholm archipelago his next step was to buy an $84,000 commercial greenhouse - as used by horticulturists for growing tomatoes - and enclose the entire home in glass.
In doing so, Sacilotto converted what had been a summer holiday home in the forest, with its own well for water, but with little insulation and no heating, into a comfortable and stylish year-round residence.
He removed the pitched roof of the wooden house, now enveloped in toughened glass, and transformed what was a dark, hidden attic space into a sunny level roof-top play area for his children, protected from the wind and rain. He installed a waste water treatment unit and composting toilet to provide nutrients and water to feed and irrigate the grapes, figs, almonds and apricots that he then cultivated in the space between the wooden house and its glass envelope which measures 200 square metres and is nine metres high.
In short, he had created what the late Swedish eco-architect Bengt Warne first designed and built for himself in the 1970s, a building typology he called a "naturhus" or "nature house": a home within a greenhouse, with space to grow fruit and vegetables from warmer climates right outside the door and no need for a mains sewage connection. A house that, as Warne said "gives architecture a fourth dimension, where time is represented by movements of naturally recycled endless flows of growth, sun, rain, wind and soil, in plants, energy, air, water and earth."
"I love living in a nature house," says Sacilotto's partner, Marie Granmar. "Here in Sweden it extends the warm season by about four months," she says. "We eat ‘outdoors' from April to October."
Thermostatically controlled rooftop openings, blinds for shading and large sliding glass doors that allow for cross ventilation all prevent the interior five-bedroom core dwelling from overheating in the height of summer, Granmar explains.
Research by Lester van Ree of the Eindhoven University of Technology, published in 2010, showed that a greenhouse residence is less likely to overheat than a super-insulated, airtight house (such as one built to the Passivhaus standard) while saving 25 per cent on winter heating bills. Further research into the science of greenhouse living is currently underway in Rotterdam where a volunteer family is living in an experimental greenhouse home designed by students of Rotterdam University.
In Sacilotto and Granmar's house, a small 6KW wood-burning stove is used for any heating required once air entering the core house has been pre-heated a couple of degrees by the greenhouse effect. However, in winter the main purpose of the "climate shell" - the greenhouse - is not for heating but protection from wind and rain.
Sacilotto was inspired to build this home after reading about another "naturhus" in Sweden, that belonged to Anders Solvarm. Solvarm's house near Vänersborg, was designed by Warne and Solvarm. Completed in 2000, it is a 145 sq metre wooden home that was constructed under the protection of a 300 square metre greenhouse of toughened glass.
Mediterranean crops and flowers now grow in abundance in beds of soil surrounding the core house and on its roof terrace. The deep soil beds are a key part of a clean and safe home sewage recycling system. Black and grey water is collected in an anaerobic settling tank for at least two days until it has formed anutrient-rich liquor. It is then pumped into the bottom of 1.1m soil beds.
"Pathogens don't survive in the deeper layers of soil," explains Solvarm. "You might say that we clean the water with a natural filter of soil where the good microorganisms in the soil are the important collaborators, just like in nature. Then the plants take the micronutrients out of the soil-filter so it doesn't get filled up. In winter, the filter stores nutrients." To err on the safe side, it is only above ground crops that are grown in the beds, such as salad crops, melons and tomatoes.
These closed-loop systems are much better for the environment than flushing our sewage down the drain to central treatment plants argues Solvarm. "Most municipal sewage systems in Sweden just clean sewage and then dispose of the nutrients," he says. "This isn't sustainable. We need to make use of the nutrients and treat them as a resource rather than send them to landfill."
To make sure there are enough plant pollinators, insects such as solitary bees are provided with habitats inside the climate shell. Contrary to expectations the interior is not humid assures Solvarm who lives in the house with his family. "Small greenhouses feel humid as they contain a high density of plants", he explains, "but most of the space in a ‘naturhus' is taken up by the core house."
And if you worry that you would feel claustrophobic in a house enclosed by a glass shell, Solvarm suggests that not all walls need be enclosed by glass. "If, say, you want bedrooms with windows that open directly to the outside, then those walls can be outside the glass climate shell," he says.
Anders Solvarm has now formed a co-operative consultancy, Greenhouse Living, to continue Warne's pioneering work and promote ‘nature houses'. The group of four engineers and architects completed its first project this year, Uppgrenna Naturhus, a cafe and conference centre near Jönköping in southern Sweden.
Like a cross between a traditional red wooden barn and a greenhouse, the building combines a vernacular style with high tech green living. Lemon trees, melons and cucumbers - watered and fertilised by the visitors' own waste - grow in soil filter beds under a glass roof in "a climate similar to northern Italy", says Solvarm.
The property, on the shore of Lake Vättern, has recently won an environmental prize from the Jönköping city authority. Greenhouse Living is now consulting on its next project, Sundby Naturhus, a family home north of Stockholm still under construction.
So, will we Brits follow our neighbours in all things Scandi? It could be an interesting way to do an eco-retrofit, as Sacilotto did.
"Britain, with its old housing stock, has lots of potential for enclosing homes in greenhouses," says Anders Solvarm. Instead of faffing about with triple-glazing and extra insulation, you could just enclose your home in a greenhouse of toughened glass and make a 25% saving in winter fuel bills. Eco-cycle sewage systems can also be retrofitted says Solvarm. Or you might be in the privileged position to employ Greenhouse Living to design you a nature house from scratch.
If so, you can bear in mind that the enclosing greenhouse need not be rectangular. In Norway, above the Arctic Circle, Benjamin and Ingrid Hjertefolger have built their home under a domed glass shell on an island near Bodo. In 2012, the couple commissioned UK company, Solardome, to erect a 15m diameter, 7m high geodesic glass dome under which the Hjertefolgers - along with volunteers from around the world - constructed a 200 sq metre, three-storey house out of cob (clay and straw).
The dome provided protection from the weather during construction of the house and continues to protect the building explains Pippa Bailey, managing director of Solardome. "The dome's shape and its 6mm toughened glass can withstand the Arctic island's high winds and heavy snow falls, unlike a conventional rectangular greenhouse," she says.
The geodesic form is also economical in materials, requiring 30% less glass than a rectangular greenhouse enclosing the same area. Flowers, fruits and vegetables grow in profusion in the enclosed 100 square metre garden and 80 square metre roof garden, watered and fed by waste from the residents.
In the UK, there are plans for a development of 16 small one-bedroom Naturhus homes enclosed in individual geodesic glass domes surrounding a larger, 20m diameter dome, housing a communal kitchen, dining area and laundry facilities. The domes will contain built-in photovoltaic panels and solar-thermal water heating.
The Vegan Eco Village, on land near Newbury, West Berkshire will treat its sewage waste in an anaerobic digester to make biogas and natural fertiliser and use waste grey water for irrigation of plants says project manager Michael Hall.
But until now nobody in the UK has completely enclosed an existing home in a greenhouse, as Charles Sacilotto did. Even though it's clearly an eco housing solution well worth considering.
Paul Miles's writing on travel, environment and architecture has appeared in The Guardian, Daily Telegraph and Financial Times. He lives a low-emissions, off-grid life on a narrowboat on which he travels the waterways of England and Wales.