The present disclosure relates generally to extruded sheet structures and, more particularly, to a corrugated, polymeric zigzag sheet suitable for implementation in greenhouse roof structures.
Traditional greenhouses are predominately covered by a single layer of glass having a thickness of about 4 millimeters (mm) or more. The glass roof structure offers both a high stiffness and a very high light transmissivity, which is important for the growing process of the various agricultural and horticultural crops found in greenhouses. One disadvantage of using glass as the greenhouse roof material is its heavy weight, which typically requires special devices/equipment during the installation thereof. Furthermore, there is the potential for breakage during installation, as well as from exposure to natural elements such as wind, snow load and hail storms. As a result, certain conventional greenhouse roof structures have implemented laminated glass or polymeric products as a greenhouse glazing.
Thin, transparent polymeric sheets (e.g., a polycarbonate sheet with a thickness of about 1-3 mm) have similar light transmission values to that of glass. However, the lack of stiffness of a flat thin sheet reduces its overall practical use in this particular application since a thin sheet does not withstand an expected wind/snow load. In addition, the lack of stiffness of a thin gauge polymeric sheet renders the installation thereof onto the construction members of the greenhouse problematic at best. Accordingly, rigid clear plastics fabricated by extrusion, roll forming and/or thermoforming processes allow for a corrugated zigzag shape that does provide a desired structural stiffness. Moreover, the zigzag shape can also reduce the amount of light lost through reflection by redirecting some of the reflected light through the roof and into the greenhouse, thereby resulting in an increase of the direct and diffuse light transmission of the roof material.
Still a further consideration is the additional insulation provided by a double walled roof panel, as opposed to the single-plate hardened glass presently used in may greenhouses. While a double-plate flat glass provides an additional measure of insulation, there is a reduction in the amount of light passed therethrough. Accordingly, it is desirable to be able to manufacture a lightweight, stiff panel that both insulates and passes an increased amount of light, but that is also easy to manufacture and assemble upon a roof structure, such as used for a greenhouse.