The Sun Pit Solar Greenhouse

A Sun Pit Solar Greenhouse:  Extend Your
Growing Season

If you live in an area with a lot of sunny clear days, then a sun pit solar greenhouse could be just the ticket to becoming self-sufficient. This kind of greenhouse relies on captured and stored solar energy, which heats the inside space during the day and allows it to be released at night.

A solar greenhouse requires some type of heat sink or thermal mass that can store the heat for slow release over night. Often this sink consists of several black barrels filled with water, a back wall of concrete, or a stone or brick floor.

What’s a sun pit solar greenhouse?

sun pit solar greenhouse

A second solar greenhouse option is the sun pit. A sun pit greenhouse just that – sunk below ground level. It takes advantage of the earth’s natural insulation as well as solar energy to create a warm growing space.

A properly designed sun pit solar greenhouse is naturally warmed at night from five sides: in an above ground greenhouse, only one side – the floor – is heated during the day.

Although not as common today as they once were, this type of greenhouse is just the ticket if you have a sunny well-drained spot for it. Pay attention to how your chosen spot drains,  since you don’t want to be working in a muddy or water filled space.

A sun-heated pit greenhouse has walls below ground level, with the roof sited above ground. The roof can be arched, A-frame, shed or rounded. I’d recommend planning either an arched or a shed roof.

An arched or rounded roof will give you the most interior space for plants. A shed roof gives you ample light, and the back wall – a good 4 t0 6 feet above ground – can be an added heat sink. Situate the length of the roof south to collect the most solar energy.

Constructing your Sun Pit Solar Greenhouse

Save your back, and rent a backhoe to excavate a space 4 feet deep and no smaller than 8X12. Dig a sump in a spot

sun pit solar greenhouseon the pit floor, about 30 inches deep and 18 inches wide, and line it with bricks. This will allow any irrigation water or seepage to be collected and pumped out.

Once the sides of the excavation are squared, build a concrete footing around the circumference and lay a mortared and filled concrete block wall on it, insulated on the outside with 1 inch rigid insulation and a layer of heavy plastic to keep out any ground water. Build the wall one block higher than the surrounding ground, keeping the block courses level and plumb.

Before adding the roof, level up the floor and either lay bricks on a bed of sand or spread 4 inches of pea gravel. At one end, plan your stairs for entry. Siting them inside the space rather than outside will help keep out any water from heavy rains.

Frame end walls  on top of the last row of concrete blocks. The end walls must be vented, and of course, one end will have the entry door. In a larger structure you will need to plan extra venting in the roof.

The apex of the roof should be at least 8 feet, but preferably 10 feet above the floor. Situate a shed roof, with a back wall on the north side. Frame in the roof. The north side of an arched roof can be covered with plywood and roofing felt, and a weatherproof covering while the south facing side will be either glass or fiberglass panels, fitted in place and sealed with weatherproofing.

Now you’re ready to add staging for your plants!

Sunk into the ground, a well built sun pit solar greenhouse takes advantage of the sun’s energy and the natural insulation of the earth. Carefully managed, it is a successful and practical alternative solar greenhouse.

Interested in building one?

Visit to find out just how pit greenhouses are being used around the world.

Read up on Sun Pit Greenhouses: My Amazon Picks

Leave a Comment: