How to Attach a Greenhouse Plastic to Metal Frame

A greenhouse isn’t complete yet without the plastic being attached to the greenhouse frame which could either be metal, wooden or PVC frame. Therefore, it is important to know how greenhouse plastics are being attached to the greenhouse frame securely in order to avoid the plastic being pulled off the frame during windy or snowy weather conditions. This text explains how greenhouse plastic is being attached to a metal frame.

Basically, there are 4 ways/methods of attaching a greenhouse plastic to a metal frame, the methods are as follows:

  • Rope-and-pressure method.
  • Snap clamps method.
  • Single-channel poly lock and wiggle/spring wire method.
  • Double channel poly lock and wiggle/spring wire method.

Rope-and-pressure method

In this method, metal components are being provided at the bottom of a metallic hoop frame at specified distances apart and at both sides of the greenhouse structure to enable ropes to be fastened to them. After the plastic is being placed over the structure to cover it, the rope is being woven back and forth from the metal component at one side of the structure, then taken over the top of the structure (securing the plastic), pulled properly to ensure the rope exerts pressure (not too much) on the plastic and then fastened to the component at the other side of the structure. This procedure is being repeated until the plastic is properly secured to the structure. This method is a low-cost method of attaching plastic to a metal frame and mostly used for smaller greenhouse structures such as a caterpillar tunnel. It can only be used for a temporary greenhouse as it will be risky to hold the plastic permanently to the frame using this method. Since there are no attachments for roll-up sides using this method, the greenhouse is vented by just pushing the plastic up the side of the tunnel in order to allow air circulate in and out of the structure.

Snap clamps method

How to Attach a Greenhouse Plastic to Metal Frame

Snap clamps are attachments used to secure plastics to round metallic pipes or tubes. They are can only be used for greenhouse structures having a set outer diameter to their metal tubing, also these clamps are manufactured in standard sizes that are suitable for 1.315 OD, 1.66 OD and 1.90 OD outer diameter tubing. They are just like round clips used to attach the greenhouse plastic to round metallic pipes or tubes, they are the most applicable where low stress and wind pressure will be applied to the greenhouse plastic e.g. making an interior partition in a greenhouse with plastic will be easily secured to the frame using a snap clamp. Using snap clamps is also one of the best attachment for fixing the greenhouse plastic to the metal roll-bar in order to make roll-up sides for venting the greenhouse. However, these clamps are not advisable to be used for installing greenhouse plastic for the top cover of a greenhouse structure because snap clamps cannot secure the plastic contiguously the entire length of the metal tube as they come in small lengths of about 4 inches as compared to the length of the tube. Snap clamps are affordable but they are only of temporary use in securing plastic to a greenhouse structure before the use of another permanent securement method as in the case of installing the corner wind panels. The only cases where snap clamps are the best option is in the case of roll-up sides and also in cases where low stress and low wind pressure will be applied to the greenhouse plastic such as an interior partition in a greenhouse.

Single-channel poly lock and wiggle/spring wire method

Attach a Greenhouse Plastic to Metal Frame

The single-channel poly lock also called C-channel, U-channel, lock channel or zig-zag wire is a component used for the permanent attachment of plastics to a greenhouse metal or wooden frame. This plastic attachment method can be used on a section of a curved metal frame. The channel is made of aluminum or galvanized steel; it has to be attached to the greenhouse frame at first in order to secure the plastic. The channel is attached to the metal framing at the points where the plastic is to be secured by using self-tapping screws (TEK screws). These self-tapping screws will drill through the channel and the metal frame underneath the channel and then secure the channel to the frame almost effortlessly, the single-channel takes shape of any metal frame that is beneath it as the TEK screws are being placed along its entire length on the frame. After the channel has been attached to the metal frame, the plastic is then secured to the channel with the wiggle/spring wire. The wiggle wire derives its name from the wiggling motion that takes back and forth over the greenhouse plastic and right into the channel. The wiggle wire completes the action of firmly attaching the plastic to the channel. The single-channel method has the advantage of creating a contiguous seal from weather and wind because the channels are installed on the metal frame one right after the other causing them to line up at their meeting ends (i.e. forming a butt up end) without any break in their span. It is a good permanent plastic securement method because the wiggle/spring wire enables the plastic to be installed and taken out without causing damage to the greenhouse plastic, this makes it possible to make an adequate adjustment to a greenhouse top cover if it was not squared with perfection at the first instance or for any other adjustment on the greenhouse. The channels are typically manufactured in 4 feet, 6 feet, 8 feet, and 12 feet pieces.

Double channel poly lock and wiggle/spring wire method:

This is simply a 2-in-1 single channel that provides twice the securement potential for greenhouse plastic, it is more rigid and robust in width compared to the single channel. The double channel poly lock serves more as a structural member of a greenhouse than a single channel poly lock. It is mostly used as a stand-alone hip rail of a greenhouse and also being a two separate channel, it permits the separate removal and replacement of plastic pieces. Double channels are produced in 6 feet, 8 feet and 12 feet sections. There are two methods by which the double channel hip rails can be attached to a metal frame for the securement of the greenhouse plastic, these are the self-tapping screw (TEK screw) method and the bolt and nut method. The self-tapping screw method is similar to that of the single-channel poly lock.

Greenhouse Plastic

For the bolt and nut method, other accessories will be needed such as two-hole straps, tension bands, channel connection plates, bolts and nuts, and self-drilling TEK screws. The tools that will be needed for this method are channel locks, vice grips, impact driver or socket wrench, drill driver, torpedo level and 5/6-inch hexagonal head driver bit. The procedures for this are as follow:

  • At first, the tension band is attached to the extreme frames of the greenhouse structure with the flat side of the tension band on the exterior of the tunnel. The ends of the tension band are being crimped with a channel lock to make it easy to get the bolts through the holes when connecting the channel.
  • Locate the slots at the back of the double channel to receive the bolt heads for the connection between the tension band and the two-hole strap. The bolt must be slide into the slot before holding the double channel in place.
  • Place the double channel on the frame securely with vice grips or clamp which serve as extra hands
  • Line up the double channel into the tension bands at the extremes with the bolts and nuts to secure the channel to the tension bands. After doing this, you must ensure the double channel ends right at the edge of the frame/hoop and then tighten the nuts to the bolts.
  • Secure the channel partially along the rest of its length to the frame using the two-hole straps and bolts and nuts, then adjust until it levels side to side on the frame/hoop with the aid of the torpedo. After it levels, the bolt and nut are being tightened.
  • Connect where two double channels meet with a splice plate. The double channel ends are screwed into the frame/hoop and are not fastened with two-hole straps. The double channels are being aligned to plumb using the torpedo.
  • Finally, for firm support of the double channel to the frame/hoop, the self-tapping screw is being used at the exterior contact between the frame/hoop and the channel while the two-hole strap with bolt and nut compensate for the interior contact between them.

After installation of the double channel to the metal frame of the greenhouse, the plastic is being secured to the double channel with the aid of the wiggle/spring wire. A finished double-channel hip rail holds the plastic to the structure with the spring wire and it is also where the roll-up side is attached to.

In conclusion, to securely attach greenhouse plastics to a metal frame permanently, the best attachment method is using a single or double channel poly lock with wiggle/spring wire, the double channel is basically the best for attaching the greenhouse plastic as a hip rail as it can replace lumber and easy to work with while for temporary attachment of plastics or interior greenhouse partitions, snap clamps will definitely fit. It should be noted however that the wiggle wire to be used in the single/double channel method of attaching greenhouse plastic to metal frames must be a PVC coated wire in order not to cut the plastic.

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