The initial decision regarding greenhouse placement, known as orientation, determines its relationship with the sun and surrounding environment. Proper orientation is the foundation for a successful growing operation, directly impacting the amount of solar energy captured and retained. This planning maximizes the light available to plants throughout the year, which is necessary for photosynthesis and healthy growth. A well-oriented structure can also significantly reduce the need for supplemental heating and cooling, lowering operational costs.
Optimal Axis Alignment for Solar Gain
For growers in the Northern Hemisphere, the standard recommendation for maximizing solar gain is to align the greenhouse’s longest dimension, or ridge line, along an East-West axis. This alignment ensures the maximum surface area is presented toward the low-angle winter sun. Since the sun’s path is lower in the sky during colder months, this orientation allows sunlight to penetrate deep into the house. This maximizes passive solar heating when external temperatures are lowest, reducing reliance on fossil fuels for warmth.
When the ridge runs East-West, the sun traces a path across the long, south-facing side of the structure from morning until afternoon. This extended exposure provides the greatest energy benefit, especially in regions with short winter days. The internal growing surfaces are warmed by the sun’s energy, which can delay or eliminate the need to activate heating systems.
While East-West alignment prioritizes winter heat gain, a North-South orientation offers a different light profile. An N-S ridge line provides a more uniform distribution of light throughout the day and across the width of the greenhouse. This alignment prevents intense hot spots and shading, making it suitable for crops requiring consistent, diffused light levels. It is often preferred in southern, high-heat climates where the priority shifts to minimizing summer overheating and managing light intensity.
Regardless of the chosen axis, the end walls will face North and South. To maximize heat retention, the North-facing wall should be designed with minimal or opaque glazing. Reducing the glass area on the North side prevents heat from radiating out, acting as an insulated barrier.
Protecting the Structure from Prevailing Winds
High winds pose a threat to a greenhouse structure by subjecting the frame to physical stress and accelerating heat loss. Wind moving across the surface increases the rate of convection, stripping away warmth and rapidly cooling the interior air. This effect increases heating demands and can strain the structural integrity of the frame and glazing panels.
To mitigate the force of high winds, the structure should be oriented so its narrowest dimension, the end wall, faces the strongest prevailing winds. This positioning presents the smallest possible surface area to the oncoming airflow, reducing the total wind load. In many locations, the strongest winter winds approach from the West or Northwest, making this the primary direction to consider.
Strategic placement of windbreaks can further protect the structure and reduce localized wind speed. A dense hedge or shelterbelt placed upwind can diffuse the force of the air before it reaches the greenhouse. The windbreak must be placed far enough away so that its shadow does not fall upon the greenhouse, particularly during low-sun winter months. A common guideline is to position the windbreak at a distance of two to five times its mature height to ensure proper wind deflection without creating shade.
Wind flow also affects the ventilation system. Vents should be positioned to utilize prevailing air currents to draw stale air out efficiently. Positioning intake vents on the windward side and exhaust vents on the leeward side ensures a gentle, consistent flow of air for effective cooling and humidity control.
Choosing the Best Physical Location
The physical location chosen must account for proper water management beneath the foundation. A site that is level or slightly elevated above the surrounding terrain is preferred to ensure effective runoff and prevent water pooling. Poor drainage can lead to damp soil around the base, increasing the risk of foundation decay, mold, and root diseases.
A primary consideration is ensuring the chosen site is free from obstruction-caused shade. Tall trees or adjacent buildings can block the sun, nullifying the benefits of proper axis alignment. It is important that no shadows fall on the greenhouse between 9 AM and 3 PM, especially in winter when the sun’s arc is lowest. The site should offer an unobstructed view of the southern sky to maximize light exposure.
Practical operational concerns influence site selection, specifically regarding utility access. Placing the structure close to a reliable water source simplifies irrigation and maintenance tasks. Proximity to an electrical connection is necessary for powering supplemental lighting, circulation fans, and heating systems.