The Greenhouse of the Future: Building a Passive Solar Greenhouse

The Greenhouse of the Future: Evaluating a Building Guide

The Greenhouse of the Future is a documentary and building guide that shows, start to finish, how a small team built a passive solar greenhouse from earth-filled tyres, recycled materials and a carefully angled glass wall. The package, released in late 2014 by filmmaker Curt Close with Anaconda Productions and the Quebec-based group SolutionEra, in collaboration with the Valhalla Movement, combines a DVD of about 70 minutes, an e-book of roughly 220 pages and construction plans. Its aim is a greenhouse that stays warm with little or no bought energy and lets a family or community grow food for most of the year.

If you are wondering whether a guide like this can help you build your own, the short answer is yes, as a starting point. It shows the principles and the work involved very clearly. But the design has to be adapted to your climate, your site and your local building rules, and the tyre walls in particular demand more skill and labour than the tidy computer drawings suggest.

What is in the package

The documentary follows the whole build, from digging the foundation to fitting the roof, and explains the reasoning behind each step. The e-book sets out the design with step-by-step instructions and drawings, and the plans give dimensions you can work from. The trailer below gives a feel for the style and the site:

A reviewer for the trade journal Video Librarian gave the film three and a half stars out of five, praising its energy and calling it a useful guide, while warning that building with tyres requires careful, precise work because no two tyres, loads of soil or workers are the same. That is a fair summary of the project's strengths and limits.

How a passive solar greenhouse stays warm

The design borrows heavily from the Earthship homes developed by the American architect Michael Reynolds in the desert of northern New Mexico from the 1970s onwards. The core ideas are simple and can work in many climates when they are applied with care.

Glazing that faces the sun. The main glass wall faces the equator (south in the northern hemisphere) and is tilted to catch as much low winter sun as possible while limiting overheating in summer.
Thermal mass. Thick walls of tyres packed hard with earth soak up heat during the day and release it slowly at night, smoothing out temperature swings.
Earth sheltering. The back wall, and sometimes the sides, are built into a slope or banked with soil, which protects the space from cold winds and loses less heat than an exposed wall.
Insulation where it counts. Thermal mass is not the same as insulation. In colder, cloudier places the mass must be separated from the frozen ground and outside air by real insulation, or it simply pulls heat out of the greenhouse.
Ventilation. Vents and openings let hot, humid air escape on sunny days, which matters as much as keeping heat in on winter nights.

Many designs of this kind also include a water tank or pond inside. Water stores a great deal of heat, and a tank can double as a home for fish in a small aquaponics system, as the illustration at the top of this page suggests.

Building with tyres and recycled materials

The signature feature of Earthship-style building is the rammed-tyre wall. Old car tyres are laid like bricks, filled with soil and pounded until each one is dense and solid, then staggered course by course. Bottles, cans and reclaimed timber often fill gaps and add decoration.

The appeal is obvious: tyres are a waste product that is cheap or free, and a packed earth wall is strong and heavy. The downside is labour. Ramming a single tyre by hand takes real effort, and a wall needs many of them. It is the kind of job that suits a community build with plenty of volunteers far better than a solo weekend project.

Rules about using tyres in buildings also vary. In Belgium, for example, using tyres in construction is prohibited because of concerns that they could leach metals such as zinc and lead, and builders there have switched to earthbags instead. Before you collect a single tyre, check what your local authority allows.

What to check before you build

A guide filmed on one site gives you a proven example, not a universal recipe. Run through these questions first:

Climate. How cold are your winters and how many sunny days do you get? Earthship buildings have struggled in cooler, cloudier and wetter places than New Mexico, where they lost heat into the ground or suffered from damp and mould until more insulation was added.
Site and orientation. Can you face the glazing towards the sun without shade from trees, hills or buildings? Is the ground well drained?
Permits. Many areas require planning or building permission for a permanent structure of this size, and unconventional materials can slow the process. Reynolds himself spent years fighting permit battles.
Snow and wind loads. A roof and glazing system that works in one region may need a stronger frame in another.
Budget and time. Reclaimed materials save money, but glazing, insulation, timber and tools do not come free, and the labour is substantial.
Ventilation and humidity. A sealed, warm greenhouse full of plants and water can become very humid. Plan vents and airflow from the start.

If in doubt, ask a local builder, engineer or experienced greenhouse grower to review your plans. A few hours of advice can save a winter of disappointment.

Other ways to grow food through the winter

The tyre-wall design is only one route to a low-energy greenhouse. Similar principles appear in sunken "pit" greenhouses dug into the ground, in Chinese-style solar greenhouses with a heavy insulated back wall and a sloping plastic front, and in simple lean-to greenhouses built against the sunny wall of a house so that the building's mass stores heat.

Even an ordinary greenhouse can be improved: add barrels of water painted dark as thermal mass, insulate the north side, and use thermal curtains at night. These changes do not create a "greenhouse of the future", but they bring some of the same benefits at a fraction of the effort.

Who this kind of project suits

A tyre-wall passive solar greenhouse is best suited to people who have land, time and helpers, and who enjoy hands-on building. Families, community gardens, schools and small farms are natural fits, especially where the build itself can become a shared project.

For them, The Greenhouse of the Future offers a clear, motivating example of what is possible with recycled materials and good solar design. Treat it as inspiration and a framework, adapt it to your own conditions, and you will have a much better chance of picking fresh greens in the middle of winter.

Sources: Video Librarian review of The Greenhouse of the Future; Global Ecovillage Network: Greenhouse of the Future; Wikipedia: Earthship; SolutionEra. Originally reported by Collective Evolution; production by Curt Close and Anaconda Productions.

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