This invention relates to a polytunnel arrangement, for example for use in the cultivation of crops to provide enhanced or optimised growing conditions for the crops.

One form of polytunnel in common use comprises a pair of rows of legs and a series of cover support hoop members, each of which is supported at one end by one of the legs of one of the rows, and at its opposite end by a respective one of the legs of the other of the rows. A flexible cover material is stretched over the hoop members and is anchored in position, defining a roof for the polytunnel arrangement.

It is often the case that a number of such polytunnel arrangements are provided side-by-side, in which case the legs may be adapted to support the ends of the hoop members of two of the adjacent polytunnel arrangements. This has the advantage of avoiding unnecessary duplication of component parts, and is also beneficial in that the spacing of the polytunnel arrangements may be reduced.

Where a number of polytunnel arrangements are provided side-by-side in this manner, then achieving a desired level of ventilation within at least some of the polytunnel arrangements can be an issue as ventilation may be achieved only through the ends of the polytunnel arrangements. In order to enhance the ventilation, it is known to provide vent arrangements whereby part of the cover, or a vent flap provided in the cover, can be rolled up, when desired, to form a vent opening in the roof. In some applications, an insect screen or the like may be provided so that when the cover or flap is rolled up, the ingress of insects into the polytunnel arrangement can be restricted despite the increased level of ventilation thereto.

It is an object of the invention to provide an arrangement in which the level of ventilation that can be achieved is enhanced. According to the present invention there is provided a polytunnel arrangement comprising a series of cover support hoop members, a first cover vent section, a drive arrangement operable to allow rolling up of the first vent section, a first securing rail whereby a part of the first vent section is attached to the hoop members, a second securing rail whereby a section of cover material is attached to the hoop members, and an auxiliary securing means whereby an upper edge part of the said section of cover material is secured relative to the hoop members at a position above the second securing rail such that the first vent section, when unrolled, is able to overlie the upper edge part of the said section of cover material.

The said section of cover material may comprise a second cover vent section, conveniently capable of being rolled up independently of the first cover vent section by a second drive arrangement. However, this need not always be the case, and arrangements in which the said section of cover material is non-movably fixed in position, in use, are also envisaged.

Such an arrangement is advantageous in that the level of ventilation that can be achieved is increased by allowing both the first and second vent sections to be rolled up, when desired, the operation of opening and closing the vent sections being relatively straightforward. When the first vent section occupies its closed, unrolled position, as it is able to overlie the upper edge of the said cover material section, for example in the form of the second vent section where provided, rainwater ingress into the tunnel arrangement is minimised. Crop damage through rainwater ingress is thus reduced.

If desired, an insect screen or hail protection netting may be provided beneath the vent section(s) such that when the vent section(s) occupy open position(s), the ingress of insects into the polytunnel arrangement is minimised, or such that crop damage arising from hailstone impacts is avoided.

The auxiliary securing means conveniently takes the form of a wire or cable or the like, extending lengthwise of the polytunnel arrangement, and around which the upper edge part of the said section, for example in the form of the second vent section, is folded. The use of a wire or cable for this purpose allows the upper edge part of the said section to lie upon the hoop members, the first vent section and the drive arrangement associated therewith being able to ride over the upper edge part of the said section with the result that a lower edge of the first vent section, when in its closed position, overlies the upper edge part of the said section. Consequently, drainage of rainwater or the like from the first vent section is onto the said section, little or no rainwater ingress into the interior of the polytunnel arrangement occurring.

It will be appreciated that the presence of the securing rail provides support for the said section, thus the auxiliary securing means is not required to bear significant loadings, in use, but rather it intended simply to locate the upper edge part of the said section in a position at which the lower edge of the first vent section is able to overlie the upper edge part of the said section. The free edge of the upper edge part may be secured to the securing rail associated therewith, if desired.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic representation illustrating a polytunnel arrangement in accordance with an embodiment of the invention; and

Figure 2 is a further diagrammatic view illustrating part of the polytunnel structure of Figure 1 in greater detail.

Referring to the accompanying drawings, a polytunnel arrangement is illustrated that comprises a series of legs 10 arranged in rows. Each leg 10 is screwed or otherwise secured to the underlying ground surface so as to occupy an upstanding orientation. Each leg 10 in one of the rows and a corresponding leg 10 in an adjacent one of the rows support respective ends of a series of cover support hoop members 12. As illustrated, the upper end of each leg 10 is conveniently of forked form to allow each leg 10 to be used in supporting the hoop members 12 of a pair of adjacent polytunnel arrangements.

A cover is positioned upon and supported by the hoop members 12. The cover is of multi-part form, comprising a first, upper section 14 secured in position by a pair of securing rails 16 clamped to the hoop members 12, and a pair of second, lower sections 18 located to each side of the first, upper section 14 and secured in position by respective securing rails 20. Each securing rail 16, 20 is, as mentioned above, secured to the hoop members 12 by being clamped thereto. The securing rails 16, 20 each include an upwardly facing channel into which a fold of the respective cover section 14, 18 extends, a suitable lock member (not shown) also being received within the channel to secure the cover section 14, 18 to the associated rail 16, 20, thus securing the cover sections 14, 18 to the hoop members 12.

Secured to the lower edges of the first cover section 14 are roller tubes 22. A drive mechanism (not shown) is provided to permit the roller tubes 22 to be drive for rotation to roll the cover material of the first cover section 14 onto the roller tubes 22, causing displacement of the roller tubes 22, the roller tubes 22 riding over a path defined by the profiles of the hoop members 12. It will be appreciated that rotation of the roller tubes 22 results in opening or closing (depending upon the direction of rotation) of vents defined by parts of the first cover section 14.

The drive mechanisms that are operable to drive the roller tubes 22 may be manually operated or may, if desired, be motorised. It will be appreciated that the drive mechanisms in combination with the roller tubes form drive arrangements for driving the first vent cover sections between open and closed positions.

The second cover sections 18 are likewise secured, adjacent their lower edges, to respective roller tubes 24 that are able to be driven for rotation to roll the material of the second cover sections 18 onto or from (depending upon the direction of rotation) the roller tubes 24 to open or close respective vents. Whilst in this arrangement, the second cover sections 18 are able to be rolled up, this need not always be the case, and they could be fixed in position. A netting or mesh screen, for example providing protection against damage by hailstones or providing protection against the ingress of insects, may be supported by the hoop members 12, conveniently supported thereon beneath the cover, securing rails 16, 20 and roller tubes 22, 24.

In accordance with the invention, this embodiment of polytunnel arrangement includes an auxiliary securing means in the form of a wire 26 extending along substantially the full length of the polytunnel arrangement and secured to the hoop members 12 thereof at a position parallel or substantially parallel to a respective one of the securing rails 20 associated with one of the second cover sections 18, but spaced above the associated securing rail 20. The upper edge part of the second cover section 18 extends over the wire 26 and is folded around the wire 26 so as to extend between the wire 26 and the hoop members 12, and is secured to the securing rail 20. As illustrated in Figure 2, the wire 26 and upper edge part of the second cover section 18 form only a very small step in the profile defined by the hoop members 12, sufficiently small that the roller tubes 22 associated with the first vent section 14 are above to ride over the respective steps, resting upon the material of the second vent sections 18, when the first cover sections 14 occupy their closed positions, thereby aiding the drainage of rainwater or the like from the first cover sections 14 onto the second cover sections 18, minimising or reducing the risk of water ingress into the polytunnel arrangement.

In use, the roller tubes 22 may occupy the closed position shown in Figure 2, in which relatively little ventilation of the polytunnel structure is provided. In this position, as mentioned above, rainwater will tend to drain from the first cover sections 14 onto the second cover sections 18. As shown in Figure 2, if desired, the roller tube 24 associated with the second cover section 18 may be rotated to partially (as shown) or fully open that part of the polytunnel arrangement. If desired, rather than increasing ventilation by adjustment of the second cover sections 18, or in additional to increasing ventilation in that manner, the roller tubes 22 associated with the first cover sections 14 may be rotated to increase ventilation in the upper part of the polytunnel cover. When the vents are open, the insect screen and/or hail netting provide protection for the crops located within the polytunnel arrangement. The risk of crop damage as a result of the increased ventilation is thus minimised.

Subsequently, when it is desired to reduce the level of ventilation, the roller tubes 22, 24 may be rotated to result in them moving back towards the position shown in Figure 2, the roller tubes 22 and lower edges of the first cover sections 14 overlying the upper edge parts of the second cover sections 18, thus restoring the ability for rainwater to drain over the cover rather than entering the polytunnel structure.

The polytunnel arrangement is advantageous in that a large vent area can be readily and quickly achieved, if desired, allowing a significant level of ventilation to be achieved, and in that, when desired, venting of just the upper section of the tunnel roof may be achieved without the need to roll up the lower edges of the roof, allowing greater flexibility and control, in use.

Whilst the description hereinbefore is of an arrangement in which vents are provided to both sides of a polytunnel arrangement, it will be understood that this need not always be the case and the invention is also applicable to arrangements in which vents are only provided to one side of a polytunnel arrangement. Furthermore, whilst the description is of the use of a wire as the auxiliary securing means, this integer could take a range of other forms without departing from the scope of the invention. By way of example, it could take the form of a rope, strap, strip of material or the like. Furthermore, the manner in which it is secured in position may take a range of forms.

In the description hereinbefore, the first vent section is able to be moved to a position in which it overlies an upper edge of a second vent section, the upper edge of the second vent section being supported by the auxiliary securing means. It will be appreciated, however, that arrangements are also possible, as mentioned hereinbefore, in which the section of material which the first vent section overlies, when closed, could be fixed rather than movable. Accordingly, the section of material need not always take the form of a second vent section. It is envisaged that it will be clamped to some or all of the hoop members, but other fixing methods may be used. A number of other modifications and alterations may be made to the arrangement described hereinbefore without departing from the scope of the invention as defined by the appended claims.