Lean-To Greenhouses

The attached, or "lean-to" greenhouse is perhaps the most practical of all greenhouses in that it actuallybecomes part of your house. Construction is easier and the structure is better braced because one wall of the greenhouse is actually your home.

Lean-to greenhouses can contribute greatly to heating your home in the winter with their passive-solar capabilities—just vent the top into your second-floor, or open up a slider or window into the space for warm air all day long.

Over at Hobby Greenhouse, they've got really simple and free plans to download basic lean-to greenhouse designs for a simple 8' x 12' lean-to greenhouse framed with 2' x 4' redwood or cedar and covered with rigid Lexan polycarbonate panels. Once the foundation is complete and all the supplies are on hand, two people can complete this lean-to greenhouse in a weekend. For energy efficiency it should be constructed around a door or window and insulated.

Backwoods Home Magazine features a first-person account of constructing a lean-to greenhouse with tips on finding inexpensive glass and troubleshooting advice. And Live Science offers information on a home that, with solar collectors working in tandem with a lean-to greenhouse, went 25 years without a heating bill.
Image from West Virginia University.

The main components of lean-to greenhouses are pretty straightforward. A lean-to greenhouse is a half greenhouse, split along the peak of the roof, or ridge line. Lean-tos are useful where space is limited to a width of approximately seven to twelve feet, and they are the least expensive structures. The ridge of the lean-to is attached to a building using one side and an existing doorway, if available. Lean-tos are close to available electricity, water and heat. The disadvantages include some limitations on space, sunlight, ventilation, and temperature control. The height of the supporting wall limits the potential size of the lean-to. The wider the lean-to, the higher the supporting wall must be.
Image from West Virginia University.

Temperature control is more difficult because the wall that the greenhouse is built on may collect the sun's heat while the translucent cover of the greenhouse may lose heat rapidly. The lean-to should face the best direction for adequate sun exposure. Finally, consider the location of windows and doors on the supporting structure and remember that snow, ice, or heavy rain might slide off the roof or the house onto the structure.
  • Location: South-facing windows will obviously get the most sun, but morning sunlight on the east side is sufficient for most plants. Morning sunlight is most desirable because it allows the plant's food production process to begin early and maximizes growth. An east side location captures the most November to February sunlight. The next best sites are southwest and west of major structures, where plants receive sunlight later in the day. North of major structures is the least desirable location and is good only for plants that require little light.
  • Glass: Glass is the highest-quality, highest-price option for greenhouses. It is the heaviest material and so can be the most difficult to install, but if installed properly and protected from shattering, glass will outlast any other plastic option in terms of useful life. It is important to have some windows that open for cross vintilation because plants can cook literally if it gets too hot! you will need to decide what transparent material will be best suited for the walls and roof or your greenhouse. Depending on your application, you may need to consider various types of glass, polycarbonate, greenhouse plastic, or other materials. Every material will have its own set of price, strength, durability, maintenance, and aesthetic considerations. Not all materials are practical in all climates or for all styles of greenhouse construction.Visit Two Green Thumbs for a great guide on figuring out what kind of glass to use.
  • Drainage: If flooding is an issue where you live, build your greenhouse above surrounding ground so rainwater and irrigation water will drain away. 
  • Size: An attached greenhouse can be a half greenhouse, a full-size structure, or an extended window structure. There are advantages and disadvantages to each type.
  • Foundations and Floors: Permanent foundations should be provided for glass, fiberglass, or the double-layer rigid-plastic sheet materials. The manufacturer should provide plans for the foundation construction. Most home greenhouses require a poured concrete foundation similar to those in residential houses. Quonset greenhouses with pipe frames and a plastic cover use posts driven into the ground. Permanent flooring is not recommended because it may stay wet and slippery from soil mix media. A concrete, gravel, or stone walkway 24 to 36 inches wide can be built for easy access to the plants. The rest of the floor should be covered by several inches of gravel for drainage of excess water. Water also can be sprayed on the gravel to produce humidity in the greenhouse.

Nicole Caldwell

Nicole Caldwell is a self-taught environmentalist, green-living savant and sustainability educator with more than a decade of professional writing experience. She is also the co-founder of Better Farm and president of betterArts. Nicole’s work has been featured in Mother Earth News, Reader’s Digest, Time Out New York, and many other publications. Her first book, Better: The Everyday Art of Sustainable Living, is due out this July through New Society Publishers.