A greenhouse is a significant investment, especially when planning to grow in an environment subject to high winds. The primary challenge is the structure’s high surface area relative to its weight, making it vulnerable to wind forces and uplift. Preparing the structure to resist these forces is more effective than reacting to damage after a storm. Structural preparation begins at the ground level, ensuring the assembly remains firmly planted, and extends through the frame design.
Foundation and Ground Anchoring Systems
The foundation is the first defense against high winds, as uplift is the primary cause of structural failure, essentially turning the greenhouse into a large kite. A permanent foundation is superior when dealing with significant wind loads. The most robust solution involves pouring concrete footings or a perimeter stem wall, providing substantial mass and a secure point to bolt the frame down. For heavier, glass-glazed structures, the footing must extend below the local frost line to prevent seasonal shifting from undermining the anchor points.
For lighter structures, or where a full concrete pour is impractical, heavy-duty earth anchors offer high-strength tie-down capabilities. Auger anchors screw deep into the ground, while duckbill anchors are driven in and toggle into undisturbed soil, both providing excellent holding power against vertical pull-out forces. The required depth and rating depend on the greenhouse’s size and the local wind speed rating. The connection point between the frame’s base rail and the foundation is equally important, requiring galvanized steel brackets, anchor bolts, or high-strength cables.
Structural Frame Design and Reinforcement
Once the connection to the ground is secured, the frame must be engineered to withstand wind pressure and suction. The structure’s shape significantly impacts its wind resistance, with curved designs generally outperforming straight-walled, peaked roofs. Quonset or gothic arch greenhouses allow wind to flow smoothly over the structure, shedding the force and distributing pressure evenly. Straight-walled designs create flat surfaces perpendicular to the wind, resulting in high pressure on the windward side and damaging suction on the leeward side.
Selecting the right material and gauge is important, with heavy-gauge galvanized steel being a common choice for its strength and corrosion resistance. The tubing’s diameter and wall thickness directly correlate to the frame’s ability to resist flex and fatigue under sustained wind loading. Reinforcement is accomplished through internal bracing, such as knee braces that diagonally connect the vertical posts to the roof rafters, and cross bracing that forms “X” shapes along the end walls and roof sections. All connections should utilize robust hardware, such as bolts and specialized gussets, rather than simple screws, to maintain structural integrity.
Passive Wind Mitigation and Site Selection
Reducing the force of the wind before it hits the structure is a cost-effective strategy. Site selection plays a large role, as placing a greenhouse in a naturally sheltered location, like the lee side of a hill or a stand of mature trees, minimizes exposure. If a naturally sheltered spot is unavailable, the structure’s orientation should be adjusted so the narrowest end, or gable end, faces the prevailing high wind direction. Presenting the smallest possible surface area reduces the overall force applied to the frame.
Windbreaks, either natural or artificial, can significantly reduce wind speed. An artificial windbreak, such as a sturdy fence or a wall of shade cloth, should be constructed with slight porosity, ideally around 50% open, to slow the wind without causing damaging turbulence. The effective zone of protection extends downwind for approximately eight to ten times the height of the windbreak. Positioning the greenhouse within this protected zone, but not too close to the windbreak, prevents the severe turbulence that occurs immediately behind a solid wall. Before a predicted storm, all vents, doors, and louvers must be securely closed and sealed to prevent wind from entering the structure, which can cause internal pressure and catastrophic roof failure.