A hoop house, often called a high tunnel, is an arched structure typically covered with plastic sheeting that provides a protected growing environment for crops. This structure extends the growing season by buffering plants from harsh weather and allowing for warmer, more controlled conditions. PVC pipe is a favored material for building these structures due to its affordability, widespread availability, and relative ease of manipulation. Selecting the correct size and type of PVC is a foundational decision that directly impacts the structure’s stability and longevity. This choice must balance material cost with the necessary strength to withstand environmental pressures specific to the structure’s planned size.
Understanding Structural Forces and Span
The determination of the appropriate PVC diameter is a direct response to the structural forces the hoop house must endure. The two primary external forces acting on the arched frame are wind load and snow load. Wind load exerts lateral stress, attempting to push the structure sideways or lift it entirely, with greater force applied when the structure is covered tightly with plastic sheeting. Snow load applies vertical compression, which is a significant downward force that can cause the arch to buckle or collapse, particularly with heavy, wet snow. The “span,” or the total width of the hoop house, is the primary factor dictating the required strength. A wider span necessitates a larger diameter pipe to maintain rigidity and resist these concentrated loads at the apex of the arch.
Recommended PVC Diameter by Hoop House Width
The width of the hoop house determines the necessary diameter of the PVC pipe to prevent failure under load. For small, temporary structures which span less than six feet wide, a smaller diameter pipe like 3/4-inch PVC is generally sufficient. These smaller pipes are highly flexible and provide enough support for the cover material over a short distance, though they offer minimal resistance to heavy snow.
Medium-sized walk-in hoop houses, typically spanning between 8 and 10 feet wide, require an increase in pipe size for adequate structural integrity. For this span, 1-inch PVC pipe is a common recommendation, offering a balance of necessary strength and ease of bending. This size provides a more robust frame suitable for taller arches that allow for comfortable access.
For larger, more permanent hoop houses measuring 12 feet wide or more, the required diameter must be increased further to manage the greater span and resulting forces. Builders often choose 1.25-inch or 1.5-inch PVC for spans up to 18 feet. Some robust designs for larger structures, especially those in high-load environments, even recommend using 2-inch PVC pipe. Regardless of the pipe diameter, any hoop house exceeding 12 feet in width should incorporate purlins or center bracing running the length of the structure to connect the arches and prevent lateral racking and apex collapse.
Selecting the Correct PVC Schedule for Durability
In addition to the pipe’s diameter, the PVC “Schedule” is a specification that defines the wall thickness and, consequently, the pipe’s strength and durability. The schedule number, such as Schedule 40 or Schedule 80, is an industry standard where a higher number indicates a thicker pipe wall for a given nominal size. Both Schedule 40 and Schedule 80 pipes share the same outer diameter, but the Schedule 80 pipe has a smaller inner diameter because of its thicker wall.
Schedule 40 PVC is widely considered the minimum standard for structural applications like hoop houses due to its balance of cost and strength. It provides a wall thickness that can resist the bending stress of the arch and the pressure from external loads. Schedule 80 pipe is significantly thicker and more rigid, but it is also more expensive and less flexible for forming arches. Thin-walled electrical conduit PVC should be avoided for permanent structural frames, as it often lacks the necessary wall thickness and UV resistance for long-term outdoor use.
Practical Tips for Bending and Arch Installation
Forming the arches requires a pipe length that is significantly greater than the width of the final structure, estimated by considering the desired height and span. A simple rule of thumb for calculating pipe length is to add the desired height to the width of the structure and then multiply that sum by a factor of 1.5. It is generally recommended to purchase standard 20-foot lengths of pipe and join them with couplers for wider spans, ensuring the stress of the bend is not placed directly on the joint.
For cold bending PVC, the process is less prone to cracking on warmer days, as the material is more pliable. To install the arches, the pipe is bent over anchor points, typically rebar stakes driven into the ground at an angle or into a wooden baseboard. The inner diameter of the PVC arch pipe must be large enough to slide over the rebar anchors, or a slightly larger diameter pipe section can be used as a sleeve for the arch pipe to slide into, providing a secure and stable connection to the ground.