I've wanted a Walipini (or an underground, passive-solar greenhouse) for years and years. Imagine walking into one with snow on the ground. What a peaceful, tranquil place full of growing things.

Lynda

https://youtu.be/3-HCemR3u7c

By Carolanne Wright

With staggering food prices and shortages looming, there’s no better time to grow your own produce. Sadly, most greenhouses are expensive to build and impractical to heat during cold, wintery conditions. Thankfully, a solution is found with the Walipini. Developed for South American mountainous regions over twenty years ago, it allows edibles to be grown year-round – even in the most inhospitable weather. As an added bonus, it’s also outrageously inexpensive to construct.
Unlimited growing season

Known as a pit or underground greenhouse, the Walipini utilizes the advantages of passive solar heating along with earth sheltering properties. The structure makes use of thermal mass energy, creating a highly efficient and cost effective method for heating the interior. Regardless of where you live, produce can be grown year round with the Walipini. According to the creators at the Benson Institute:

“The Walipini, in simplest terms, is a rectangular hole in the ground 6′ to 8′ deep covered by plastic sheeting. The longest area of the rectangle faces the winter sun — to the north in the Southern Hemisphere and to the south in the Northern Hemisphere. A thick wall of rammed earth at the back of the building and a much lower wall at the front provide the needed angle for the plastic sheet roof. This roof seals the hole, provides an insulating airspace between the two layers of plastic (a sheet on the top and another on the bottom of the roof/poles) and allows the suns rays to penetrate creating a warm, stable environment for plant growth.”

The Institute continues with an explanation of how the earth acts like a battery, storing heat during the day while releasing it during cooler nighttime temperatures:

Energy and light from the sun enter the Walipini through the plastic covered roof and are reflected and absorbed throughout the underground structure. By using translucent material, plastic instead of glass, plant growth is improved as certain rays of the light spectrum that inhibit plant growth are filtered out. The sun’s rays provide both heat and light needed by plants. Heat is not only immediately provided as the light enters and heats the air, but heat is also stored as the mass of the entire building absorbs heat from the sun’s rays.

The estimated building cost (using volunteer labor) for a 20 x 74 foot Walipini in La Paz, Peru is between $250 – $300. Taking advantage of inexpensive materials like PVC pipes and ultraviolet (UV) protective plastic sheeting add to the savings.

A detailed do-it-yourself building manual can be found here and includes crucial instructions for ventilation, waterproofing and drainage.

https://wakeup-world.com/wp-content/uploads/2014/10/walipina_benson.pdf

If you do decide to build a walipini in the northern latitudes, you will need to think carefully about your roof slope and the angle of the sun during the winter solstice to ensure there is no shading in your greenhouse. To overcome this issue, you can build an earth berm on the northern side of the greenhouse to create a steeper roof slope.

https://www.youtube.com/watch?v=mobajU3F5zY