A hoop house, often called a high tunnel, is a simple, unheated structure designed to create a modified microclimate for plants. It operates by trapping solar radiation, which warms the air and soil inside, similar to the greenhouse effect. This passive solar heating allows gardeners to significantly extend their growing season, starting earlier in the spring and continuing later into the autumn or even winter. The structure also provides a physical barrier, shielding delicate crops from harsh weather elements like frost, heavy rain, strong winds, and pests.
Planning Site Selection and Materials
The location of your hoop house directly influences its performance, making a full-sun exposure site the most beneficial choice. Sunlight absorption is necessary for the passive heating mechanism to function effectively. A gentle slope is preferable for natural water runoff, preventing pooling inside the structure that can lead to disease. Proximity to a reliable water source simplifies irrigation, which is necessary in the warmer, contained environment.
The structure requires a robust base, typically constructed from pressure-treated lumber (such as 4x4s or 2x6s) to resist ground moisture and decay. For the curved ribs, galvanized electrical metallic tubing (EMT) conduit is preferred over PVC for its superior strength and longevity, especially where snow loads or high winds are a concern. The covering film must be a UV-stabilized, 6-mil thick polyethylene greenhouse film, formulated to resist degradation and maximize light transmission. Securing hardware includes ground anchors, self-tapping screws, and aluminum wiggle wire channels to hold the film tautly.
Constructing the Frame and Securing the Base
Begin by defining the footprint of the structure, ensuring the corners are square using the 3-4-5 triangle method before installing the base lumber. The pressure-treated wood must be securely fastened together at the corners using heavy-duty galvanized brackets or long structural screws. Ground anchors, such as rebar stakes driven through the inside of the base frame and into the soil, prevent the structure from shifting under external forces.
The hoops, or ribs, provide the curvature and strength for the covering and are typically spaced between four and six feet apart along the length of the base. If using EMT conduit, a specialized hoop bender tool is used to achieve a uniform arch shape. Each hoop is then secured to the base frame, either by inserting the ends over rebar sleeves driven into the ground or by fastening directly to metal base plates screwed to the lumber.
To maintain the structural integrity of the arched frame, a ridge pole or purlin must run along the peak of the hoops. This purlin, often another piece of EMT conduit, connects the tops of all the ribs, preventing lateral sway and collapse. Additional diagonal bracing may be installed at the corners and along the sides to reinforce the frame against wind gusts. Consistent spacing and secure attachment of all components distribute environmental loads evenly.
Applying the Polyethylene Covering
Applying the polyethylene film requires careful execution, ideally on a calm, windless day to prevent uncontrolled billowing. The film is unfolded and centered over the completed frame, ensuring adequate overhang on all sides and ends. This film is designed with anti-drip additives and light diffusion properties to optimize the growing environment by scattering sunlight and minimizing condensation.
The process begins by securing one long side of the film to the base frame using a permanent method, such as batten tape and screws or an aluminum channel system. The wiggle wire channel is a highly effective method where the film edge is held tightly in a track by a spring-steel wire. Once the first side is secured, the film must be pulled tightly over the frame to the opposite side, minimizing wrinkles and slack that could lead to wind damage.
Achieving proper tension is paramount; the film should feel drum-tight to reduce flapping, which prematurely degrades the plastic and stresses the frame. The film is then secured to the second long side using the same channel or batten system, ensuring the tension is maintained. Excess film hanging past the base is typically rolled up tightly and fastened, leaving enough material at the ends to be incorporated into the end walls. If two layers of film are used for insulation, they are sealed around the edges and inflated using a small air pump, creating a thermal barrier.
Creating End Walls and Ventilation Systems
The end walls close off the structure and incorporate necessary access points, typically framed using standard construction lumber like 2x4s. These walls are built as flat frames that match the arch of the hoops and are secured to the end ribs and base frame. Integrating a hinged access door into one end wall is standard practice, allowing for easy entry and equipment movement.
The polyethylene film is stretched over the newly framed end walls, pulled tight, and secured to the lumber using batten strips or staples, which are then covered with thin wood strips for protection. The film must be cut around the door opening, leaving overlap material that can be sealed with specialized greenhouse tape or integrated into the door frame. This creates an airtight seal, maintaining the internal temperature.
Controlling the internal temperature and humidity is necessary, as solar gain can quickly raise the temperature far above desirable levels. Passive ventilation is commonly achieved by installing roll-up sides, which allow the lower third of the film along the long sides to be raised manually or with a crank system. This draws cooler air in at the base and exhausts hot air through the opening, creating a chimney effect. Vents can also be integrated into the upper portion of the end walls to provide cross-ventilation, assisting in the regulation of heat and moisture.