Small-Greenhouse Plans for Winter Growing

Forget simply stretching the season by a matter of weeks. Our innovative small-greenhouse plans take solar gain to the nth degree, with a design that’s optimized for winter growing. We’ll show you how to build a greenhouse that’s free-standing and features low-cost glazing and a simple foundation.


| February/March 2016



Smart Greenhouse Design

Our smart greenhouse design features a south-facing glazed wall that's angled to capture the maximum amount of winter sunlight and heat.


Illustration by Len Churchill

Almost anyone can build an affordable greenhouse to start seedlings in spring or extend the growing season by a month or two in fall. But building a greenhouse designed for harvesting cool-season crops all winter long is quite another matter. Happily, that’s just what our winter greenhouse plans offer, and any handy gardener can tackle this project with basic tools, a good helper and a couple of free weekends.

Lately, loads of products promising that you can “grow food indoors” during winter using artificial lights are hitting the market. Don’t be fooled — replacing free sunlight with expensive and far less intense electric lighting is not a sustainable choice. These small-greenhouse plans feature a south-facing glazed wall that’s angled to capture the maximum amount of winter sunlight and heat. The north wall, side walls and roof are insulated to retain as much solar-generated warmth as possible on cold nights. In many regions, these strategic design elements will allow the greenhouse to stay warm enough to support cool-season crops through the coldest, snowiest months without the need for any supplemental heat or light. (For top winter crop choices, see Winter Gardening Tips: Best Winter Crops and Cold-Hardy Varieties.)

Consider These Options for Your Homemade Greenhouse

Our design will produce a solar-heated, 8-by-8-foot structure, but you can easily modify these small-greenhouse plans to suit your needs and site. You can purchase new materials from a home improvement center, or you can recycle components from another structure, the local Habitat for Humanity ReStore or your stockpile. Make sure you select the doors before you begin building because their dimensions will affect the stud spacing. Also, check with local authorities about building codes and permits. Some municipalities exempt small structures; others require a permit. You’ll also need to consider the following options before you build.

Timber base. We used three rows of landscape timbers to create this greenhouse’s knee wall, but you can add extra rows to help level a hilly site, or to provide more headroom above or planting room below. We chose timber because it’s relatively inexpensive and is easy to work with, but you may prefer to build a knee wall from 2-by-6s so you can insulate between them.

Wall angle. The southern wall is glazed with ribbed polycarbonate and set at a 60-degree angle for optimum heat intake from the sun (aka “solar gain”) in winter. The farther north you live, the lower the sun will be in winter. Lindsey Schiller of Ceres Greenhouse Solutions in Boulder, Colorado, says an angle equal to your latitude plus 20 degrees will yield the maximum transmission, but you can actually deviate from this angle by as much as 30 degrees and only lose about 5 to 8 percent of potential transmitted light. So, the 60-degree angle of our south wall works well for most U.S. locations. A conventional vertical wall would perform similarly if outfitted with a glazed roof.

Roof pitch. We settled on a metal roof with a pitch ratio of 3/12 (about 14 degrees) for good runoff. You can make yours steeper or flatter depending on your site and needs. The interior of the roof is sheathed with polystyrene to make up for metal’s poor insulating qualities.





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