Greenhouse Design & Building Tips
Garden year around
If you are typical of most people once they have caught the gardening bug, you are probably dreaming of a small greenhouse. It may seem like a luxury, but really once you have one, nothing could be further from the truth. A small greenhouse can be tucked into all but the tiniest lots and can be creatively designed to be energy efficient, functional, and aesthetically delightful.
A green house is valuable for
- raising plants for winter use indoors.
- carrying over garden plants to be used as stock for next season.
- starting tender plants and annuals early from seed.
- increasing plant variety and succession of bloom.
- easily cultivating winter vegetables in pots or boxes below the benches.
- experimenting with new varieties.
Kits are available in a range of materials and prices, but for a motivated do-it-yourselfer, a small greenhouse can be constructed affordably for a relatively small cash outlay. Lean-tos against garage or house take advantage of an existing wall and are particularly inexpensive, though siting is particularly important. The primary advantage of a purchased greenhouse kit is that many of the details such as dealing with high humidity, leakage, and ventilation have already been considered and dealt with in the design. Someone building a small greenhouse from scratch needs to consider these issues to prevent problems that might result in premature failure or plant loss.
Tips for building your own greenhouse
The following tips will help you design and build your own greenhouse.
- Start with a standard design using easily available materials. Consider your preferences. Charming greenhouses have been built using recycled window sashes, remilled wood, and repurposed doors. Supremely energy efficient greenhouses have been engineered from polycarbonate and strawbale construction.
- Accommodate your climate to create specific solutions depending on your location, latitude, and climate.
- Site to maximize sunlight, especially in winter. A good south or southeast exposure is best. If the long wall has a south exposure and is twice as long as it is wide, it naturally collects solar energy.
- Speaking of solar: Paint inside heat storage surfaces red or dark blue to collect energy and reflect light useful to plants. Other surfaces should be white or foil covered to reflect light. Double glazing cuts heat loss. Insulate the structure's perimeter and inside unglazed walls.
- Design to use standard sizes. Most materials are available in multiples of 4.
- Consider your gardening habits when designing. Growing tropical plants is different from overwintering vegetables.
- Are you going to want a heat source and if so, what type? If properly sited, the solar gain can be captured to minimize the need for additional heat except on the very darkest of winter days.
- Thermostats and timers can regulate just the right amount of additional heat or light.
- Water is a necessary convenience. Plumb lines for water and power can use the same trench. An electric on-demand water heater can provide the convenience of hot running water for scouring old pots. An electrical supply can regulate the thermostat for temperature, provide heat, and power fans. Two 15-amp circuits can power an electric heater, lights and fans.
- Design a back-up plan in case of power outage or severe weather conditions.
- If using wood, build your greenhouse from cypress, cedar, or redwood, though regular wood painted and maintained will suffice. Pressure treated wood for framing is a cost-effective option.
- Glass-paned windows are traditional, but fiberglass, polycarbonate plastic, acrylic, and plastic film can be used. Each material has its relative advantages and disadvantages, so research your selection. Polycarbonate is particularly energy efficient and reduces the need for lots of additional heat. Glass is aesthetic, but subject to breakage.
- Permanent foundations to support the building are suggested, but flooring is not. A gravel floor several inches deep allows adequate drainage. A concrete, stone, or gravel walkway between benches provides stable footing. Pressure-treated wood works for small greenhouses; larger structures benefit from poured concrete.
- Open coated wire shelving allows a free flow of air around plants. If you use wood for shelving, leave about a half-inch gaps between boards to facilitate ventilation.
- Use thermally-activated vents that open and close without electricity.
- Plan to accommodate half to two-thirds of your plants on benches. Leave some floor space for large containers and very tall plants.
Resources
Books
Building Your Own Greenhouse: Greenhouse Basics
Greenhouse Gardener's Companion: Growing Food & Flowers in Your Greenhouse or Sunspace
Hire a carpenter to help frame your greenhouse. ContractorNexus can help you locate a qualified pro in your city.
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