A hoophouse, often referred to as a high tunnel, is an unheated, plastic-covered structure that uses passive solar energy to create a protected growing environment for crops. This structure is a powerful tool for home gardeners and small-scale farmers looking to extend their growing seasons. By protecting plants from wind, heavy rain, and early or late frosts, a hoophouse allows for earlier spring planting and later fall harvesting than traditional open-field gardening. Building a hoophouse involves straightforward construction techniques to secure an arched frame and cover it with specialized film. This guide provides a practical overview of the planning and building process to help you create a durable, functional structure.
Designing Your Structure and Collecting Materials
Planning is necessary to ensure the hoophouse performs optimally in its location. The site should be as level as possible and offer maximum sun exposure, typically running north to south to maximize light distribution. Good drainage is also important, as standing water inside the structure can create overly humid conditions that encourage plant disease.
You must first determine the size of your structure, considering the width and height needed for crop rows and comfortable working space. The frame material is the next major decision, with builders choosing between flexible PVC pipe or stronger, galvanized electrical metallic tubing (EMT) conduit. EMT conduit, while requiring a bender, provides a more rigid and durable frame, offering greater longevity.
For the covering, you will need specialized UV-resistant polyethylene plastic film, which is different from common clear plastic sheeting. This film is typically 6-mil thick and formulated to withstand constant sun exposure, often lasting four to six years before needing replacement. Creating a materials list ensures you have the correct pipe, lumber for end walls and baseboards, and all necessary hardware.
Securing the Base and Foundation
The foundation resists the uplift forces caused by strong winds, ensuring the structure’s long-term integrity. Begin by preparing the site, ensuring the ground is clear of debris and the soil is relatively even. Next, stake out the exact dimensions of the hoophouse, using string lines to establish square corners and straight sides.
Anchor points secure the entire structure to the earth, typically involving driving pieces of rebar or heavy-duty ground posts into the soil at regular intervals. These anchors should be driven 2 to 3 feet deep to provide substantial resistance against lateral movement and wind shear. If using baseboards, which are highly recommended for added stability, they are attached directly to these anchors and must be perfectly level along the perimeter.
Treated wood baseboards provide a solid surface to fasten the hoops and are also used later to secure the bottom edge of the plastic covering. The entire base must be anchored firmly to the ground before the hoops are installed.
Erecting the Hoops and Support Frame
Once the base is anchored, the next step is to raise the arched ribs that form the main structural body of the hoophouse. These hoops are secured to the foundation anchors, typically by sliding the ends of the pipe or conduit over the exposed rebar stakes driven into the ground. The hoops should be consistently spaced, usually between 4 and 6 feet apart along the length of the tunnel.
If using EMT conduit, the material must be bent evenly into a semi-circular shape using a specialized pipe bender jig sized to the conduit’s diameter. Proper bending ensures that each rib is uniform, which is necessary for the plastic covering to lie flat and tension correctly. The hoops are then connected and stabilized by a ridge pole, or purlin, which runs along the highest point of the structure.
The purlin is a length of pipe or wood fastened to the apex of every hoop, acting as a brace to prevent the hoops from swaying or collapsing inward. Securing the purlin with clamps or bolts adds significant rigidity and distributes wind or snow load evenly across the entire frame.
Applying the Covering and Finishing Touches
The final stage involves enclosing the frame and installing components for crop management. Simple end walls are framed first, typically using lumber, to provide rigid support for a door opening and ventilation flaps. This framework is essential for allowing access and controlling the internal climate.
Draping the polyethylene film over the entire structure should be done on a calm, windless day to prevent the large sheet from becoming unmanageable or torn. The plastic must be pulled taut both width-wise and length-wise to achieve proper tension, which prevents flapping that can quickly degrade the material. Securing the plastic is often done by fastening it to the baseboards using specialized channels and “wiggle wire,” which locks the film into place.
Alternatively, the bottom edge of the plastic can be buried in a narrow trench around the perimeter, using the soil weight to create a seal and provide tension. Basic ventilation is established by installing roll-up sides along the length of the house, which are managed manually to control internal temperature and humidity. These roll-up sides allow warm, moist air to escape and facilitate passive cooling, creating a stable environment for plant growth.