WO2005029941A2

WO2005029941A2 - Greenhouse having an openable and closeable vent

Info

Publication number: WO2005029941A2
Application number: PCT/US2004/030295
Authority: WO
Inventors: Hans Schultz
Original assignee: Sps Corporation
Priority date: 2003-09-24
Filing date: 2004-09-16
Publication date: 2005-04-07
Also published as: WO2005029941A3

Abstract

An inexpensive greenhouse vent is achieved by using a bendable vent panel at the apex of a glazed greenhouse roof and fastening a central portion of the vent panel to a ridge at the apex and bending and bowing opposite sides of the vent panel upwardly or downwardly between the closed and open venting positions. A larger air flow and larger vent opening are achieved when using a raised ridge located above the roof glazing panels and bowing the sides of the vent panel down to a closed position and bowing the sides of the vent panel upwardly to an open position. A gutter may be provided on the raised ridge to collect water infiltrating between overlapped, corrugated ends of adjacent vent panels. Other gutters may be provided on a vent rail and vent header to discharge water into a drain channel that also collects water discharging from the ridge gutter with the drain channel carrying the water down to discharge into a main gutter for the greenhouse. The vent header, vent rail and vent panels may be preassembled together on the ground and raised into position and attached to the greenhouse frame members. Then, the vent rails and vent headers may be detached from one another to allow raising of the vent rails from the vent headers which results in a bending of the vent panel to its open position.

Description

GREENHOUSE HAVING AN OPENABLE AND CLOSEABLE VENT

Field of the Invention This invention relates to a greenhouse and to a venting system for venting the interior of the greenhouse.

Background of the Invent ion This invention relates to an improved venting system for a greenhouse such as a thin film greenhouse or the type shown in U.S. Patent No. 6,089,973 wherein the greenhouse was comprised of a frame and. large, flexible panels of semi-rigid plastic such as polycarbonate panels. These panels are usually corrugated and semirigid and are used on greenhouses in some instances for replacing thin films which were supported on a frame. In some greenhouses, these semi-rigid glazing panels are flat, i.e., not bent into a curve, on the roof. In other instances, the polycarbonate, semi-rigid panels are usually bent to fit an arched roof and include an upper portion where there is a central vent . These large flexible roof panels are often supported by a curved structural support comprising curved structural arches and transverse horizontally extending purlins supported on the curved arches . Typically these greenhouses of this construction vary from 20 feet to 40 feet in width. The roofs are usually supported by columns varying in height from 10 to 14 feet. The roof support usually comprises structural arches usually bent within about a 12 foot to 25 foot range of radius. These curved rafter supports are usually round tubes of about 1.5 to 3inches in diameter. Typically, the translucent or transparent glazing panels supported on this curved structural support are about four to six foot wide panels which are corrugated in their longitudinal length direction and may extend up to thirty-nine feet in length. These glazing panels are not brittle or frangible-like glass which can easily shatter. The glazing panels are rigid compared to the very thin, plastic films often used for inexpensive greenhouse constructions . As disclosed in U.S. Patent No. 6,089,973, an inexpensive venting system can be achieved by bending outer ends of such glazing panels to create vent openings at the top of the greenhouse. The inherent flexibility of these panels allows them to bend between their open and closed positions without the use of a separate hinged vent framework at the top of the greenhouse. The bending of the ends of the flexible panels disclosed in the aforementioned panel provides a much cheaper construction for the venting of the greenhouse than a conventional greenhouse ventilating sash formed of a window-like portions which are pivotally hinged and have elaborate constructions for providing the vent. The height of the vent opening is limited due to the minimum bending radius that can be used without risking a cracking of the bent panel . There is also a need for an inexpensive venting system in plastic film greenhouses many of which do not have a vent. Typically, these plastic film greenhouses have only a single longitudinal ridge member at the curved peak of the greenhouse and curved roof arches that are spaced apart in the range of 5 feet to 10 feet and furnish the only support for the roof, i.e., there are no longitudinally extending purlins. The film is typically a polyethylene film that comes in rolls having a width in the range of 15 to 25 feet and a length of several hundred feet. The film is unrolled in the longitudinal direction of the greenhouse and fastened at the four edges in special male and female type plastic profiles. Worldwide, film greenhouses are the most common type of greenhouses and would use an improved and inexpensive venting system. An important aspect of a greenhouse is a proper water drainage system to drain away condensation as well as infiltrating water which may be considerable if the roof vent is open and it is raining. If the roof vent is open above the horizontal when it is raining, rain water will flow down the inside of the raised vent panel and needs to be drained away. Thus, there is a need for an inexpensive vent panel system with a drainage feature for condensation and infiltrating water at the roof vent. Summary of the Invention In accordance with the illustrated embodiment, the greenhouse is provided with a new and improved, inexpensive vent which provides a large vent opening for ventilation of the interior of the greenhouse. In the preferred embodiment, this is achieved by providing a raised ridge at the upper apex of the greenhouse and positioning a flexible vent panel on the raised ridge at a location substantially above the roof so that a vent opening is formed when the ends of the flexible panel are bent upwardly away from the fixed roof glazing panels. In accordance with the preferred embodiment, the greenhouse is provided with a ridge and an integral, semi-rigid panel has its center portion fastened to the ridge and has its panel ends lifted forming an open venting position spaced above the roof panels to allow air flow into or from the greenhouse interior and a closed position blocking air flow into or from the greenhouse. The ends of the glazing panels are connected to an actuator or lifter that pulls or pushes on the panel ends to bow the panels about their center portion which is fastened to the raised ridge. In some instances, the ridge will be a raised ridge raised above the fixed roof glazing panels or film material to provide a raised vent panel which can be bent to provide a larger vent opening. In other instances, the ridge will not be raised, and the bendable vent panel will be secured to the ridge or purlin at the peak of the roof to be bent upwardly therefrom into the open position. Preferably, the ridge supporting the bendable panel is provided with a gutter that collects condensate or infiltrating water when the vent panel is raised at its edges to the open position. The gutter on the ridge carries the water to a space or gap between adjacent ridges through which the water discharges into the curved drain channel which is bent to follow the curvature of arches or arch rafters for discharge into a main gutter. An inexpensive method of assembling and positioning the bendable vent is provided and comprises a temporary securing of the vent rail and vent header together on the ground. The assembly is then lifted into position at the peak of the roof and secured in position. Then, temporary securing of the vent rail and vent header is undone. The preferred temporary securing is done by self-drilling, tapping screws which fasten the vent rail and header together and then removing the screws after the assembly has been lifted and secured in position on the arch members. After the vent rail and vent header have been fastened in place on the arch members, the vent panel is draped over the ridge and the ends of the panel are fastened to the vent rails at opposite ends of the vent panel. Brief Description of the Drawings FIG. 1 is a view of a greenhouse having a flexible, raised ridge vent panel in accordance with one embodiment; FIG. 2 is a view of a greenhouse having a non- raised vent panel constructed in accordance with a another embodiment; FIG. 3 is a cross-sectional view of a curved drain channel; FIG. 3a is a view of a curved rod lifter having a bracket to prevent unwanted lifting of the vent panel; FIG. 3b illustrates the shape of the drain channel; FIG. 4 is an enlarged view of the vent ridge, drain channel and an elevating support post for the raised ridge supporting the vent panel at its center; FIG. 5 is an enlarged view of a purlin vent header, vent rail and vent lifter in accordance with one embodiment; FIG. 6 is a fragmentary, cross-sectional view of a gutter which receives infiltration or condensate water from the vent panel; FIG. 7 is a fragmentary view of a fixed glazing panel supported by a purlin which is mounted on a curved rafter; FIG. 8 is a vent comprised of a vent panel secured to a non-raised, ridge purlin which is supported on a curved arch; and FIG. 9 is an elevational view of a drain channel having an end positioned over the edge of a main gutter. Detailed Description of the Preferred Embodiment A greenhouse 10 is shown in FIG. 2 without a raised ridge at the top of the greenhouse and the greenhouse comprises support columns 12 and a curved roof 14. The roof is formed of glazing panels 15 of semi-rigid, plastic material. These semi-rigid sheets are preferably corrugated as described in U.S. Patent No. 6,089,973, which is hereby incorporated by reference as if fully reproduced herein. Briefly the greenhouse shown in FIG. 2 has a roof support which includes elongated curved arch or rafters 16 and which are typically made of a rounded tube or pipe to define the curvature for the roof of the greenhouse. Typically the width between the support columns for the illustrated greenhouse varies from about 20 to 40 feet with the columns extending about 10 feet to 14 feet; these sizes being given by way of illustration only and not by way of limitation. The. glazing sheets 15 are bent to curve over the curved rafters and are laid on purlins 20 which extend generally horizontally and are supported by the rafters. The glazing panels 15 are usually 3 to 6 feet in width and are usually equally spaced along the roof. Three purlins 20 are shown in FIG. 2 for the respective left-hand side of the roof and for the right-hand side of the roof. Manifestly, the number of purlins or the elimination of purlins can be made as desired depending on the size and the kind of greenhouse. Often a truss support 22 is provided beneath the rafters and includes a central horizontal beam 26 and inclined, triangle defining struts 27, such as shown in FIG. 2. In the greenhouses shown in FIG . 2 , a flexible vent panel 28 is secured to a central ridge 30 at the upper center of the greenhouse curved roof . This non- raised ridge is supported by the curved rafter 16. The vent panel 28 has a pair of opposed ends 32 each of which can be raised from a solid line lower closed position 34 to an upper dotted line open position 36 where the ends 32 are spaced above the upper ends 15a of the glazing panels 15 as shown in FIG. 2. A greenhouse such as shown in FIG. 2 would have about an eighteen inch vent opening between the upper bowed end 32 of the flexible vent panel 28 and the adjacent upper purlin 20a. In accordance with a preferred embodiment of the invention, as illustrated in FIG. 1, a larger opening and better ventilation is achieved for the greenhouse 10 by having a raised ridge 30 (FIG. 1) supporting a central portion of the venting panel 28 at a position located above the roof 14 to provide a larger vent opening 29 than that provided with the constructio shown i FIG. 2 which lacks a raised ridge. This increase in vent opening and air flow therethrough is achieved by fastening the central portion of the flexible vent panel to the raised ridge 30 (FIG. 1) which allows the ends of the venting panels to be bowed downwardly as shown in solid lines to the closed position 34 and then to be bowed upwardly as shown by the dotted line position to provide the larger vent opening. The use of the raised ridge and the bowing up and down of the raised vent panel results in an increase of about 50 percent in the illustrated embodiment over the non-raised ridge embodiment shown in FIG. 2. Of course, the vent opening extends longitudinally for the length of the greenhouse so that the increase height of the fifty percent opening is extended and provides a substantial difference in the volume of air flowing into the greenhouse to provide better ventilation. Manifestly, the amount of opening increase may vary substantially and the fifty percent is given by way of example only. The ends 32 of the vent ends 28 are raised by a lifter 40 (FIG. 5) that may take many forms from a manual pole-like lifter to a common motor driven lifter extending longitudinally of the greenhouse beneath each of the respective vents in the roof. Herein, the lifter comprises a long rod 41 (FIGS. 3A and 5) having a rack 42 thereon which engages a rotatable pinion gear 43 mounted on a drive shaft 44 that is turned to rotate the pinion gear and shift the rack vertically to either raise or lower the vent panel end 32 which is pivotally attached to the upper end of the rack rod by a pivot pin 46. A straight or curved lifter rod 41 (FIG. 3A) may be used to open the ends of the lightweight vent panel. Unlike the heavy frame of the hinged conventional vents used heretofore, the vent panel 28 is very light and carries only a vent rail 50 (FIG. 5) at each of its opposite ends. There are no rigid side rails on the vent panel. High velocity winds and internal pressures may exert forces on racks 41 trying to move them upwardly and to break the seal between the vent rail 50 and the vent header 52 thereby allowing infiltration of water if the racks are at the conventional acute angle. Herein, the vent lifter rod 41 is preferably installed at about 90" to the vent rail, as illustrated in FIG. 5 to may it more difficult for the lifter rod to be pulled upwardly. When the lifter rod is at 90", the entire weight of the rack needs to be lifted straight upwardly while most of the lifting wind force is at a diagonal across the inclined top surface of the vent panel at about 90' to the lifter rod. Alternatively, a retainer bracket 44 (FIG. 3A) or other device (not shown) may be provided to retain an acute angle, curved lifter rod 41 (FIG. 3A) against undesirable upward travel due to high velocity wind flow over the vent that tries to lift the vent panel rail 50 from the vent header 52. Sometimes it is desired to use a curved lifter rod at an acute angle to keep the lower end of the rod from protruding into a horizontally extending, insect screen positioned in the upper peek of the greenhouse. Disposing the lifter rod at about a right angle to the vent header 52 is cheaper than providing and installing a retainer bracket to prevent opening of the vent panel to high velocity air flow thereacross . In accordance with another aspect of the invention, each raised ridge 30 is provided with a ridge gutter 53, as best seen in FIG. 4, to collect water on or forming condensation on the underside of the panels . When the vent is open and it is raining or condensation is collecting on the inside surface of the vent panel, particularly where the vent panel is raised to the open position, water or condensation will flow down the interior surface of the vent panel toward the ridge where it is collected in the ridge gutters 53. Herein, the ridge gutters 53 may be inexpensively formed from a bent metal or extruded metal piece that has upturned lower edges defining channels 53a. The water being collected in the channel 53a flows longitudinally to discharge at the end of the ridge member. Herein, the ridge members are usually ten to thirty feet in length and are spaced at their ends from one another by a small space, e.g., 1/8 to 1/4 inch and the water flowing in the channel to its end drops and discharges into an underlying curved drain channel 48 that is on the underside of the roof. The curved drain channel 48 is shown in FIGS. 3 and 4 as being very lightweight, inexpensive, channel-shaped, members that can be bent and curved to follow the curvature of the roof. The drain channels 48 have upper ends 48a at the ridge gutters 53 and carry the water downwardly to discharge into main gutter 60 for the greenhouse. The main gutter 60 carries away the water collected from a series of curved drain channels 48. The main gutter 60 is primarily a primary member that functions as a horizontal structure to which lower ends of the fixed roof panels 15 are attached and secondarily serves as a gutter. As best seen in FIGS. 9 and 10, a lower end 48b of the drain channel 48 extends beyond lower ends 15a of the glazing panels 15 which are screwed to upper end flange end 60a of the main gutter. This lower drain channel end 48b extends over the gutter 60 to discharge water into this main gutter 60. Plastic filler strips 49 fill the spaces on the underside of the corrugated glazing panel 15 and rest on the main gutter flanges end 60 and are notched out (FIG. 10) to allow the drain channel 48 to rest directly on the upper flange end 60a of the main gutter. Because the drain channels 48 are fastened to the underside of the supporting purlins 20 by screws or the like, the drain channel ends 48a need not be fastened to the main gutter flange end 60a. Turning now in greater detail to the illustrated raised ridge shown in FIG. 4, the raised ridge 30 is supported on an upstanding post 55 which is attached to the truss curved rafter 16. The vent panel 28 is simply fastened to the raised ridge by means of threaded fasteners 56 or other means of fastening. The posts 55 support a short upper or top plate 57 to which the raised ridge is fastened by fasteners 58. In existing greenhouses without a venting system, the ridge elevating post 55 may be bolted or otherwise attached at each of the curved rafters 16 located beneath a vent panel 28. Herein, the ridge elevating post has a bottom flat plate 55a (FIG. 4) secured by fasteners 58a to the top of the ridge post to raise the ridge and the vent panel substantially above the existing curved rafter to provide a higher volume of air flow into and from the greenhouse interior. The height of the post is usually 8 to 12 inches to which must be added the height of the ridge 30 to which the vent panel is secured by the fasteners 56. The height of the raised ridge and vent panel may be as required, but it is usually limited by the fact that the bending of the vent panel 28 about too small a radius may stress, crack or break the flexed vent panel . To provide an inexpensive ridge 30 and gutter 50, the ridge 30 may be an inverted channel member (FIG. 4) having top, horizontal web 30a disposed between a pair of vertical legs 30b which are integrally attached to and carry the two gutters 50. The gutters 50 are defined by a bottom channel wall 50a integrally attached to lower ends of the vertical legs 30b and upturned vertical flanges 50b integral with the channel wall 50a. The ridge 30 and gutter 50 can be made in other ways that are more expensive such as by an upper extruded part to which the vent panel 28 is secured and a separate gutter extrusion part located below the upper extruded part. In any event, it is preferred to provide a longitudinally extending ridge 30 that is merely a purlin located at the ridge to support the vent panel 28 as the purlins 20 support the glazing panels 15. As explained and illustrated, it is preferred that the purlins 20 and ridge 30 be inexpensive, hollow, metal members usually having a rectangular cross-section. To provide an inexpensive venting system without the expensive and heavy frame of conventional hinged venting systems, a universal vent header 52 (FIG. 5) is provided that is mounted and secured to the top purlin 20a by a suitable fastener 65. More specifically, the preferred vent header has a horizontal leg 66 overlying the top wall of the purlin and fastened thereto by the fastener 65. A downward flange 67 is positioned against the vertical leg of the upper purlin to resist lateral downward pulling by the stationary glazing panels 15 which have their upper ends mounted in a channel defined by a pair of integral, inclined spaced header flanges 68 and 68a. The illustrated glazing panels are corrugated and a block of filler material 70 is positioned over the exterior side of the corrugations to extend to and to abut the underside of an upper header flange 68 which projects over the glazing panel ends positioned in the channel defined by the flanges 68 and 68a. The vent header 52 also serves to support and seal with the vent ends 32 at the vent rail 51. To this end, the body of the vent header has an upper portion 72 that is abutted by a portion 51a of the vent rail. Herein the upper portion 72 is an inclined wall section sloped at the same slope as the inclined vent rail portion 51a resting thereon. The header 52 has a upstanding center body section 52a which is integrally joined to the lower end of the inclined wall section 72 as well as to the flanges 68 and 68a and to the horizontal leg 66 attached to the top purlin 20a. To provide an inexpensive vent rail 51 on the vent panel 28, it is preferred to provide a one-piece member that has a first portion which is attached to the lifter rod 41 by the pivot pin 46 and that has a second portion 51a that seals with the vent header 52. The vent rail is structurally stiffened by having a vertical portion 51b and a lower channel-shaped end 51c. The illustrated vent rail 51 is fastened to the underside of the vent panel ends 32 with these ends resting on top of the inclined vent rail portion 51a projecting upwardly from this inclined portion 51a is a block supporting legs 76 which carries a block 78 of solid plastic that fills the corrugations on the upper side of the vent panel 28. These header block supporting legs 76 having a pair of depending bracket supports 79 to which is fastened a pivot pin bracket 80 by fasteners 81. The pivot pin bracket may be U-shaped with a pair spaced depending sidewalls 82 which support opposite ends of the pivot pin 46 with the upper end of the vent lifter 41 pivotally mounted on the pivot pin 46 and positioned between the bracket depending sidewalls 82. The top purlin 20a may also be provided with a pair of channel-shaped portions 90 and 90a, as best seen in FIG. 5 to stiffen and strengthen the top purlin. The bottom walls of these web-shaped portions 90 and 90a are secured by fasteners 91 to underlying curved arches or rafters 16. The use of the lightweight, bendable vent panel is also applicable to inexpensive greenhouses that usually have only one long ridge at the peak of the greenhouse and lack any purlins and use thin films of plastic such as polyethylene film rather than glazing panels of rigid polycarbonate or the like. In such a film greenhouse, if no ridge purlin is present, a ridge purlin would be added and fastened to the curved rafters 16, as shown in FIG. 8. The latter illustrates the vent panel 28 being used without an elevating post 55 as used in the above-described raised ridge environments. The vent panel 28 is shown as being a corrugated, polycarbonate sheet in FIG. 8. It is to be understood that the vent panel may be a non-corrugated, flexible panel of solid plastic which bends between the open and closed positions. Indeed, the vent panel could be a plastic, non-corrugated, flat flexible and bendable sheet, in any of the embodiments of the invention. The vent panel 28 of FIG. 8 bends between the open and closed positions. Top purlins 20a would be added to and fastened to the curved arches 16 to which would be attached the vent header 52 for cooperation with a vent rail 51 secured to ends 32 of the vent panel. The plastic film could be attached to these top purlins 20 or to the vent header 52. Suitable lifters 40 would be attached to the vent rail 51 to bend the plastic vent panel 28 between its open and closed positions. The curved arches 16 are typically bowed and are spaced about 5 to 12 feet apart in a film type of greenhouse. Manifestly, the roof may be made of various other materials than the described polyethylene film that comes in rolls of long length and the described long length polycarbonate sheets of corrugated plastic and still fall within the purview of the appended claims. In the embodiment illustrated in FIG. 2, a greenhouse is shown without a raised ridge 30 and an elevating post 55, as shown in FIGS. 1 and 4. The non- raised vent panel wall will be attached to the peak roof purlin 30. In the embodiment of FIG. 2, the existing peak purlin, that is the same as the other existing purlins, can be retained or a ridge purlin 30 with attached gutters may be substituted for the existing purlin on the arched rafters 16. In the embodiment of FIG. 2, purlins 20 support the glazing panels 15 and there is a roof truss support 22 having struts 27 and a horizontal beam 26 at the bottom of the truss support. In the embodiment of FIG. 2, the roof and truss support are supported on the upper ends of vertical columns 12 at the sides of the greenhouse. The greenhouse roof supporting structures described herein are only typical and numerous other kinds of supporting structures could be used. In the non-raised ridge greenhouse, the vent panel does not open as far as the vent panel does in the raised ridge greenhouse because the non-raised vent panel does not bend down as far to get to the closed position as does the raised ridge vent panel. Because a large volume of air flow is often desired, greenhouse owners may prefer to spend more money to add elevating posts 55 and raise the ridge 30. In both the non-raised and the raised ridge venting systems, ridge 30 will preferably have the gutters 50 to collect condensate or infiltrating water and suitable drain channels 48 will be used to remove the water collected by the ridge gutters. Thus, the venting as well as the water removal are preferred to be used, although the venting system may be provided with a ridge purlin that is not associated with a gutter to provide only air venting without water removal. In accordance with another important aspect, the method of assembly of the venting may be improved. In the conventional installation process, two or more people climb around and over the roof structure several times and at a considerable height and on a minimum of framework to support them. This is relatively time- consuming and expensive'. ,In the preferred process, the vent rail 51 is temporarily secured to the vent header 52 on the ground as, for example, by self-threading screws that are later unscrewed and taken out. That is, the assembler on the ground assembles the vent rail 51 and vent header 52 and joins them by the temporary screw fasteners. Then, the assembled vent panel assembly of the vent rail and vent header are lifted and secured to the ridge purlin 30 and to the upper purlin 20a. Then, the screw fasteners can be removed allowing the vent rail to be separated away from the vent header when bending the bendable vent panel to the open position. The bendable vent panel is secured to the ridge by fasteners and the opposite ends of the bendable are fastened to the vent rails. Thus, there is provided a new and improved method of assembling of a venting system.

Claims

What Is Claimed Is; 1. A greenhouse having an openable and closeable vent for venting air to and from a greenhouse interior; a frame; a roof supported on the frame and being formed of light admitting, glazing material; a vent for the greenhouse located substantially centrally and above an upper portion of the roof; a ridge on the frame for supporting the vent of the ridge of the greenhouse roof; a bendable vent panel on the vent having a central portion mounted on the ridge and bendable between an open position to allow air ingress and egress and a closed position; and an actuator for flexing ends of the panel between the closed position to close the vent opening and the open venting position which allows air flow into or from the interior of the greenhouse.

2. A greenhouse in accordance with Claim 1 comprising: the ends of the vent panel being bowed downwardly from a central position to the closed position and being^" bowed upwardly above the central position to the open venting position.

3. A greenhouse in accordance with Claim 2 wherein the vent opening is defined when the ends of the vent panels are bent to the open position and is at least about 27 inches in height.

4. A greenhouse in accordance with Claim 1 comprising: a gutter associated with the ridge to collect condensate or water infiltrating through the vent.

5. A greenhouse in accordance with Claim 4 comprising: a condensate removal system having drain channels for collecting water from the gutters associated with the ridge.

6. A greenhouse in accordance with Claim 5 wherein the gutters are attached to the ridge; the ridge gutters delivering water to the ends of the ridges at which the water flows from the gutters into the drain channels.

7. A greenhouse in accordance with Claim 5 wherein the drain channels are curved, plastic channels bent downwardly to follow the roof to its lower end.

8. A greenhouse in accordance with Claim 1 comprising: arch frame members in the frame; an elevating post secured to the top of arcri frame members and having the ridge secured to the upper end of elevating post.

9. A greenhouse having an openable and closeable vent for venting air into and from an interior of a greenhouse, the greenhouse comprising; a roof formed of light admitting glazing members; a raised ridge on the frame for supporting the vent above the greenhouse roof; a flexible vent panel formed of semi-rigid plastic material having a central portion mounted on the raised ridge portion to be positioned substantially above the roof; outer edge portions on the vent panel being bowed downwardly from the raised ridge to a closed position with the roof therebeneath and bowed upwardly to a position extending and positioning the ends above the raised ridge to enlarge the vent opening.

10. A greenhouse in accordance with Claim 9 comprising: an actuator for flexing the ends of the vent panel to bend the same about the raised ridge between the downwardly bowed closed position and the bowed upwardly bowed open position.

11. A greenhouse in accordance with Claim 9 comprising: a gutter associated with the raised ridge to collect condensate and infiltrating water through the vent .

12. A greenhouse in accordance with Claim 9 comprising: an elevating post secured to an underlying frame to raise the vent panel above the remainder of the roof.

13. A greenhouse in accordance with Claim 9 comprising: a vent rail secured to outer edge portions of the vent panel; and a vent header secured to the roof frame for cooperating with the vent rail when the vent rail is in the closed position.

14. A greenhouse having an openable and closeable vent for venting air to and from a greenhouse interior; a frame; a roof supported on the frame and being formed of light admitting glazing panels; a vent for the greenhouse located substantially centrally and at an upper portion of the roof; a ridge on the frame for supporting the vent above the greenhouse roof; a series of bendable, corrugated vent panels of semi-rigid plastic each having a portion secured to the ridge; an end of the vent panels being bendable about the secured portion between a closed position and an open position to define the vent for the greenhouse; and a gutter system associated with, the ridge to collect infiltrating water or condensate.

15. A greenhouse in accordance with Claim 14 wherein the corrugated vent panel comprises an integral sheet which has a minimum bending radius of at least 10 feet.

16. A greenhouse in accordance with Claim 14 comprising: a gutter associated with the ridge; and a vent rail secured to the ends of the vent panels and having gutters associated therewith.

17. A greenhouse in accordance with Claim 16 comprising: spacing adjacent ridges to provide a gap to discharge collected water from the gutters; and a drain channel having an upper end positioned to collect the discharging water.

18. A greenhouse in accordance with Claim 17 comprising: a gutter associated with the vent purlin to convey water to the drain channel.

19. A greenhouse having a roof and a roof ventilating system comprising: a frame; a roof frame supported by tlie frame; rigid roof panels of plastic supported by the roof frame to form a roof covering for the greenhouse; a raised ridge supported by the roof frame; a vent panel of rigid bendalole plastic supported at a central portion by the raised ridge; fasteners securing a central portion of the vent panel to the raised ridge; free ends on the vent panel on the opposite side of the central portion; and an actuator for lifting the free ends of the vent panel to bend and curve about its central portion fastened to the raised ridge to allow air to flow into the greenhouse to ventilate the greenhouse.

20. A greenhouse in accordance with Claim 19 wherein the actuator pulls the outer free ends of the vent panel to bend and curve downwardly to a closed position and pushes the outer free ends of the vent panels to bend and curve upwardly to a vent open position.

21. A greenhouse in accordance with Claim 20 wherein the actuator comprise: a rack and a pinion gear for shifting the rack vertically.

22. A greenhouse in accordance with Claim 19 comprising: a drain associated with the raised ridge to carry away water infiltrating between adjacent vent panels .

23. A greenhouse in accordance with Claim 19 wherein a series of vent panels are secured to the raised ridge, each of the vent panels being corrugated and having overlapping corrugations at longitudinal edges of the panels .

24. A method of providing ventilation in a greenhouse comprising: providing a roof with fixed, rigid plastic glazing panels and a raised central ridge; securing a central portion of a vent panel made of bendable rigid plastic to the raised ridge; and bending the opposite ends of the bendable vent panel about a central portion thereof between a closed position and an open venting position to allow air to flow through a vent opening into the interior of the greenhouse .

25. A method in accordance with Claim 24 wherein the bending of the opposite ends of the vent panel comprises bending the ends to bow downwardly to a closed position with, respect to the fixed roof panels and bending the ends to bow upwardly to an open position spaced with respect to the fixed panels.

26. A method in accordance with Claim 24 comprising: providing a gutter system at the raised ridge; and collecting in the gutter system water infiltrating through overlapped ends of adjacent, vent panels .

27. A method of constructing a greenhouse having a vent system with a bendable vent panel at the ridge of a greenhouse roof comprising: providing a pair of vent rails; providing vent headers for securing to purlins; temporarily fastening the vent rails and vent headers together into an assembly; raising the assembly into position and attaching the same to the roof of the greenhouse; securing a vent panel at its opposite edges to the vent rails of the assembly; and removing the temporary fastening of vent panels and the vent rails together to allow the vent panel to be bent between open and closed positions.

28. A method in accordance with Claim 27 wherein the temporarily fastening of the vent rails and headers together comprises tack welding of the header and rails together.

29. A method in accordance with Claim 27 comprising: providing a ridge to be secured in a raised position relati-ve to fixed glazing panels of the roof; and securing a center portion of the vent panel to the ridge.