GB2531796A

GB2531796A - A geotextile

Info

Publication number: GB2531796A
Application number: GB1419440.1A
Authority: GB
Inventors: Oliver Andrew Dunderdale David
Original assignee: Cha Tech Group PLC
Current assignee: Cha Tech Group PLC
Priority date: 2014-10-31
Filing date: 2014-10-31
Publication date: 2016-05-04
Also published as: GB201419440D0

Abstract

A geotextile for use in green-roof systems is formed as a unitary mat having fibres defining a first region 301 and a second region 302. The inter-fibre separation in the second region is greater than that of the first region. The number of fibres in the second region may be less than the number of fibres in the first region and the inter-fibre separation may be graduated throughout the thickness 303 of the fabric or just in a transition portion (702, Figure 7) between the regions. Alternatively, the interface between the regions may be abrupt. The fibres may be hydrophilic and may have a round or multi-lobal cross-section. The fibres may comprise a core with a sheathing of lower melting point than the core, and the textile may be consolidated by melting the sheathing. Alternatively consolidation can be by needle punching. The first region may comprise fibres of 0.1 to 20 decitex, and the second region may comprise fibres of 40 to 300 decitex. The first region may be a water retaining and distribution region and the second region a drainage and support region.

Description

A GEOTEXTILE

The present invention relates to a geotextile for use in a green roofing system.

A roof upon which plant growth is encouraged is referred to as a "green roof". Buildings are the most common location for a green roof, although other roofs may be suitable, for example the roof of a boat. A roof may be designed from the outset to be a green roof, or alternatively may be retrofitted with a green roof arrangement. In both cases, a green roof comprises plants growing in a growing medium, the growing medium being located on the roof along with other functional layers. Typically, the growing medium is placed on top of other layers of the green roof, making the plant growing medium the outermost layer of a green roof. There are generally two types of green roof installations: extensive and intensive. Extensive green roofs require little to no maintenance, however they also have much less biodiversity than intensive green roofs. In general, extensive green roofs are not accessible to the public. In contrast, intensive green roofs require substantially greater maintenance, but is allow a much wider biodiversity than extensive green roofs. In general, intensive green roofs form roof-top gardens or other public-accessible areas.

The implementation of a green roof, either intensive or extensive and either by design or having been retrofitted, has a number of benefits for both owners of the building it is installed on and for people living or working in the surrounding area. These benefits are multifactorial, including environmental, financial, aesthetic, or combinations thereof.

In implementing green roof systems, a feature of particular importance is how the green roof manages the flow of rain water. Due to the water retentive properties of a green roof, particularly of the water-management layers, the flow rate of rain water from a green roof to the ground is retarded. As a consequence of this, the quantity of water entering a drainage system is more evenly distributed over time. This retardation of flow rate reduces the risk of the drainage system being overwhelmed by a large amount of water in a short period of time (e.g. particularly heavy bouts of rain). This reduction of risk reduces the possibility of flooding or damage. This water retention (and so retardation of flow rate) must, however, be balanced with construction constraints, for example the load bearing limits of the roof. An additional advantage of the water management performed by a green roof relates to the filtering of pollutants by the growing-medium. A green roof may reduce the quantity of these pollutants entering the drainage system and the water system in general.

In addition to the advantageous water management properties, a green roof also provides thermal insulation to the roof of a building. This insulating property reduces heat loss through the roof of the building, thus reducing heating costs. In addition to the heat loss minimisation, an additional feature of green roofs are their ability to deflect incident solar energy, thus decreasing undesirable temperature increases inside the building to which the green roof is fitted. Clearly the additional heat management properties of a green roof reduce energy consumption in general, and so give both environmental and economic benefit.

Furthermore, green roof structures protect the underlying roof from damaging effects of the environment. For example, ultra-violet sunlight has a significant detrimental effect on the long term integrity of many traditional building materials. A green roof blocks ultra-violet sunlight from impinging on the underlying roof structure, and so avoids this detrimental effect.

Another advantage from green roof structures is the mitigation of the "heat island effect". This is effect can be summarised as the significant temperature increase measured within urban centres. Structures made of traditional building materials absorb solar radiation and then re-emit it as heat; this can lead to temperature increases on the order of several degrees Celsius. In contrast, solar radiation incident on a green roof will often be converted, via photosynthesis, into glucose or other organic compounds, by the vegetation present on the green roof and thus decreases the temperature of the surroundings.

For these and other reasons, green roofs are becoming an increasingly popular option for environmentally conscious development.

Conventional green roof arrangements comprise a number of layers, each fulfilling a different function. As is well known in the art, drainage and water-management is often provided in the form of a cuspate layer formed of durable plastic. Fig. 1 illustrates a traditional green roof water management system, having such a cuspate layer in addition to a filter layer and a protection mat. The filter layer is provided so as to ensure that the cuspate layer does not become clogged with soil or other elements of growth-medium and also to prevent the growth-medium from washing-away. The protection mat is provided so that the relatively hard cuspate layer does not abrade or puncture any layers below it. In installing a conventional green roof generally two methods are used. The cuspate, filter, and protection layers are either combined prior to installation or during installation. In combining the layers prior to installation the layers are generally un-wound from a rolled form, glued together at contact points between the layers, and then rolled back up ready for transport. However, doing this causes increased processing costs to manufacture a finished product. Alternatively, combining the layers during installation would incur additional costs, for example crane costs, as additional layers must be transported to the roof. In addition to this, additional installation time is required which is an increased health and safety risk.

It is an object of the present invention to provide an improved geotextile for use in a green roof.

According to the present invention, there is provided a nonwoven geotextile for use in a green roof, the geotextile being formed as a unitary mat comprising a plurality of fibres, and wherein in cross-section it has: a first region having a first average inter-fibre separation; and a second region having a second average inter-fibre separation; wherein the second inter-fibre separation is greater than the first inter-fibre separation.

Optionally, the first region of the geotextile has a first density of fibres per unit volume and the second region of the geotextile has a second density of fibres per unit volume, wherein the first number of fibres per unit volume is different to the second number of fibres per unit volume.

Conveniently, the first number of fibres per unit volume is larger than the second number of fibres per unit volume.

Advantageously, the geotextile has a graduated transition in inter-fibre separation between said first and second regions.

Optionally, the graduated transition is present through substantially the whole cross-section of the geotextile.

Advantageously, the graduated transition is present through a part of the cross-section of the geotextile between the first region and the second region.

Optionally, the geotextile has an abrupt interface in inter-fibre separation between the first inter-fibre separation of the first region and the second inter-fibre separation of the second region.

Conveniently, a portion of the fibres are selected from: round cross section fibres, hydrophilic fibres, bi-component fibres, multilobal fibres, or any combination thereof.

Advantageously, 30% by weight of the fibres in the geotextile are bi-component fibres.

Conveniently, the bi-component fibres include an inner core and an outer sheath, the sheaths of said bi-component fibres being fused to one another.

Optionally, the inner core of said bi-component fibre has a first melting point, and said outer io sheath of said bi-component fibre has a second melting point, the second melting point being lower than the first melting point.

Advantageously, 35% by weight of the fibres in the geotextile form the first region. Conveniently, 35% by weight of the fibres in the geotextile form the second region.

Optionally, the fibres within the first region are multi-lobal fibres, hydrophilic fibres, or round cross-section fibres.

Advantageously, the fibres within the second region are round cross-section fibres.

Conveniently, the geotextile has an uncompressed thickness within any one of the following ranges: 5mm and 50mm; 25mm and 35 mm; 10mm and 45mm; 15mm and 40mm; 20mm and 35 mm; 25mm and 30mm; 20mm and 45mm; and 25mm and 45 mm; or any combination of any two limits of any of the disclosed ranges.

Conveniently, the first region comprises fibre having a linear mass density within any one of the following ranges: 0.1 -20 decitex; 1 decitex -20 decitex; 2 decitex -18 decitex; 5 decitex -10 decitex; 2 decitex -7 decitex; 1 decitex -10 decitex; or any combination of any two limits of any of the disclosed ranges.

Advantageously, the second region comprises fibre having a linear mass density within any one of the following ranges: 40 decitex -300 decitex; 40 decitex -100 decitex; 50 decitex -decitex; 60 decitex -90 decitex; 70 decitex -90 decitex; or any combination of any two limits of any of the disclosed ranges.

Optionally, the geotextile has a basis weight within any one of the following ranges: 400 2000 g/m2; 800 -1200 g/m2; 500 -900 g/m2; 500 -1500 g/m2; 500 -900 g/m2; and 800 -900 g/m2.

Advantageously, the first region is a water retaining and distribution region of the geotextile. Optionally, the second region is a drainage and support region of the geotextile.

Conveniently, the fibres are polymeric fibres and at least some of the fibres are fused to one another.

Advantageously, the geotextile is installed within a green roof structure.

Optionally, the geotextile is installed between a growth substrate layer and an underlying roof structure.

Conveniently, the geotextile is installed between a growth substrate layer and an insulation layer.

is Advantageously, the water retaining and distribution region of the geotextile is adjacent to the growth substrate.

Optionally, the drainage and support region of the geotextile is adjacent to the insulation layer.

Advantageously, said plurality of fibres may comprise natural fibres.

So that the invention may be more readily understood, and so that further features thereof may be appreciated, embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a cross-sectional view of a green roof structure known from the prior art; Figure 2 is an exploded perspective view of the cuspate, filter, and protection layers of the green roof structure of Figure 1; Figure 3 is a perspective view of a geotextile in accordance with the present invention; Figure 4 is a schematic drawing showing an arrangement of fibres forming a first region of the geotextile having a first average inter-fibre separation Figure 5 is a schematic drawing similar to that of figure 4, but which shows an arrangement of fibres of a second region of the geotextile having a second average inter-fibre separation Figure 6 is a cross-sectional view of a geotextile in accordance with the present invention; and Figure 7 is a cross-sectional view of a geotextile in accordance with the present invention as installed within a green roof.

Turning now to consider the drawings in more detail, there is shown in figure 1 a green roof system as known in the prior art. This system has a growth medium layer 101, a filter layer 102, a cuspate layer 103, a protection mat 104, a waterproof membrane 105, an insulation layer 106, a vapour control layer 107 and a plywood deck 108. These layers all perform varying functions, as denoted by their names. The growth medium layer 101 is placed on the is outermost surface of the green roof system such that plant life has space to grow. The filter layer 102 is placed directly underneath the growth medium layer 101 so as to prevent soil or other fine particles being transmitted to layers below. Underneath the filter layer 102 is the cuspate layer 103, which is discussed in more detail below, but which functions as a water retaining and drainage layer. The cuspate layer 103 is directly atop a protection mat 104, which is in turn directly atop the waterproof membrane layer 105. This waterproof membrane layer 105 is provided to ensure that water does not ingress to the insulation layer 106 which is directly below the waterproof membrane layer 105. Below the insulation layer 106 is a vapour control layer 107, and below the vapour control layer 107 is the plywood deck 108. The entire system would be installed atop a roof of a building or other suitable structure with the plywood deck in contact with the roof of the structure. Of particular note in figure 1 is the filter 102, cuspate 103 and protection 104 layers of the system which will be discussed in more detail and with relation to figure 2.

The filter layer 102, as shown in figure 2, is generally a water-porous material used to allow water to drain to the cuspate layer 103 whilst ensuring that fine particles such as soil or other elements of the growth medium do not clog or block the cuspate layer 103. A further feature is that the filter layer 102 prevents the growth medium from being washed away as water progresses through the green roof system.

The cuspate layer 103, as shown in figure 2, traditionally comprises an array of cups 201 or recesses formed into a sheet of plastic. These cups 201 act to retain water which has drained through the filter layer 102 and also to drain away excess water once the cuspate layer 103 has reached capacity. It is important that the cuspate layer 103 retains sufficient volume of water so that plant life may grow in the growth medium layer 101. This water retention also gives rise to the advantageous effects discussed above, namely the retardation of water flow to any drainage systems downstream from the green roof. The cuspate layer 103 is generally formed of a hard durable plastic, as it must be able to withstand the load of the layers above it whilst maintaining the cups 201 in a usable shape.

Considering the protection mat 104, as shown in figure 2, this is conventionally a felt or other fibrous layer which is used to protect the waterproof membrane 105 below from the hard cuspate layer 103 by cushioning the cups 201. This is important in such systems, because if the cuspate layer 103 were allowed to rest directly on the waterproof membrane there is a substantial risk of point-loading which could result in puncture of the waterproof membrane. Undesirably, this would allow water draining through the system to ingress towards the insulation 106 or vapour control 107 layers and inevitably to the roof structure below.

To install the green roof system shown in figure 1, the layers would generally be laid down sequentially, starting with the plywood layer 108, across the roof of the structure.

Turning now to figure 3, this is a perspective view of a geotextile mat 300 in accordance with the present invention, and which comprises a plurality of nonwoven fibres. The geotextile mat 300 has a first region 301 and a second region 302. In the orientation of the mat shown in figure 3 the first region is located towards the top of its cross-sectional thickness, and the second region is located towards the bottom of its cross-sectional thickness. Both of the regions 301, 302 comprise nonwoven fibres. In some embodiments of the present invention, the geotextile may have an uncompressed thickness between 5mm and 50mm and in particular examples the uncompressed thickness of the geotextile may be between 25mm and 35mm.

The first region 301 is of different configuration to, and distinct from the second region 302 in that the fibres 401 of the first region 301 are more densely packed than the fibres 501 of the second region 302. This packing density is discussed in more detail below, but by more densely packed it is meant that there is substantially less space between the fibres 401 of the first region 301 than there is between the fibres 501 of the second region 302. In the illustrated embodiment there is a graduated transition 303 between the first and second region, which extends substantially throughout the cross-sectional thickness of the geotextile. This graduated transition is formed by the change of the packing density of the fibres with respect to depth of the geotextile mat 300. In some embodiments of the geotextile, 35% by io weight of the fibres in the geotextile form the first region, but in other embodiments it is possible for 35% by weight of the fibres in the geotextile to form the second region.

It will be appreciated that in order to form a geotextile as described above, the material from which it is constructed should have certain desirable qualities such as certain water retention and drainage rates, as well as being of a suitable weight and density. It has been found that, as discussed above, a suitable material for a preferred embodiment of the invention is a nonwoven textile. Nonwoven textiles and their production are described below. Further described are a number of properties of a nonwoven textile material that are beneficial to a geotextile constructed therefrom. In some embodiments, the fibres which form the geotextile are polymeric fibres, and at least some of the fibres are fused to one another to form a unitary mat.

A nonwoven textile is a material in which a number of generally randomly orientated fibres are interlinked and/or connected to form a sheet-like textile. The fibres are not woven together in an orderly fashion (e.g. as warp and weft) as in conventional woven textiles, but are instead interlinked and/or connected randomly. This is depicted schematically by the randomly-laid nature of the fibres 401, 501 shown in figure 3. A nonwoven textile material may include a plurality of interlinked natural and/or synthetic fibres. In the present invention, it is envisaged that these synthetic fibres may be polymeric fibres such as, for example, polyester or polyactide (PLA) fibres. However, it is to be understood that other materials may be suitable, including polypropylene, polyethylene terephthalate etc. Notably, fibres suitable for a geotextile according to the present invention are include: fibres which are round in cross section; fibres which are multilobal (for example trilobal or pentalobal) in cross section; fibres which are hydrophilic and so attract water; bi-component fibres as described below; or any combination of these. In some embodiments, the fibres in the first region are trilobal fibres, hydrophilic fibres, or round cross-section fibres, and in some embodiments the fibres in the second region are round cross-section fibres.

Alternatively, the fibres may be naturally occurring, either from animals (for example wools), or from vegetable matter (for example bast fibres). The fibres may also be semi-synthetic in their manufacture, for example viscoses/rayon, as are known in the art. These fibres may be used to produce a nonwoven textile in the manner described below.

Figure 4 is a schematic drawing which represents the fibres 401 of the first region 301. The fibres 401 in this region are relatively closely packed (and so have a high packing density) and therefore the average separation between fibres of the first region 301 is relatively low. This is represented in the schematic by the average inter-fibre separation "x". The voids or gaps 402 between the fibres 401 in figure 4 are thus relatively small.

Figure 5 is a schematic drawing corresponding generally to figure 4, but which shows the is distribution of fibres in the second region 302 of the mat. Here "y" denotes the average inter-fibre separation of the second region 302. As will be noted, "y" in figure 5 is clearly larger than "x" in figure 4. Thus the packing density of the second region 302 is substantially lower than that of the first region 301. As will also be appreciated, in the embodiment represented by figures 4 and 5, the second region 302 is configured so as to have a lower number of fibres per unit volume than the first region 301. The voids or gaps 502 between the fibres 501 of the second region 302 as shown in figure 5 are relatively large as compared to the first region 301.

The packing density or average inter-fibre separation of fibres can be controlled via a number of means. Preferably the number of fibres per unit volume may be increased or decreased so as to respectively increase or decrease the packing density of fibres, as indicated above and shown in figures 4 and 5. Alternatively, however, it is envisaged that the diameter of the individual fibres could be increased or decreased, which would of course respectively decrease or increase the inter-fibre separation between individual fibres. Generally the diameter of a fibre with a given density is measured by decitex (mass in grams per 10,000 metres) or linear mass density and so this value could be controlled in order to determine the average inter-fibre separation. In some embodiments, the linear mass density of fibres within the first region is selected to be between 1 decitex and 20 decitex. Likewise, in similar or other embodiments the fibres within the second region are selected to have a linear mass density within the range 40 decitex -300 decitex, although it is envisaged that in some embodiments the preferred range of linear mass density will be 40 decitex to 100 decitex.

The space or voids 402, 502 between fibres 401, 501 (determined in part by the inter-fibre separation x and y) of the respective regions, and preferably the first region 301, is used to retain water. Notably, the first region 301, or indeed both regions, can be seeded with hydrophilic fibres. An example of a hydrophilic fibre which could be used is the Cirrus 0 fibre.

This choice of fibre, in combination with the relatively low average inter-fibre separation allows the water retaining properties of at least the first region 301 to be substantial in comparison to the prior art. Indeed, in comparison to the cuspate layers of the prior art, substantially all of the first region 301 may be used for water retention as opposed to only the cups 201 of the cuspate layer 103 in the prior art arrangements.

As discussed above, the inter-fibre separation substantially defines voids 402, 502 between the fibres. Liquid may remain temporarily trapped in these voids, making the textile substantially porous and retarding the flow of water through it. In the context of the present invention, liquid inside the geotextile does not simply flow through the geotextile, but instead this flow is delayed as some liquid becomes retained in the voids 402, 502.

Figure 6 is a cross-sectional view of a green roof system utilizing the present invention, and thus shows the geotextile described above installed within the green roof system. In this system, growth medium 101 is placed atop the geotextile mat 300 invention, the geotextile mat having a first region 301 and second region 302 as described above. The geotextile mat 300 is placed atop the waterproof membrane 105, which is in turn atop the insulation layer 106, vapour control layer 107, and plywood deck 108.

In this embodiment, it is not necessary to install a separate filter 102 or protection layer 104 such as those shown in figure 1. This is because the average inter-fibre separation, as determined by the number of fibres per unit volume or the diameter of fibres, of the first region 301 is sufficient to act both as a filter and as a water retention and distribution means.

Further, as the second region 302 comprises a relatively soft fibre, in comparison to the hard cuspate layer 103 of figure 1, it may rest directly atop the waterproof membrane 105 without risk of point-loading or puncturing the waterproof membrane 105. It is envisaged then that in embodiments of the present invention, the first region 301 acts as a water retaining and distribution region which, due to its fibrous structure, provides a capillary action to permit the distribution of retained water to the growth medium above. This offers advantages over the prior art cuspate arrangement which can provide insufficient water distribution to the growth medium in the event that an air gap forms between the growth medium and water retained in the cuspate layer during relatively dry periods. In the arrangement of the present invention it has been found that the above-mentioned capillary action still occurs in relatively dry periods io so long as there is at least some water moisture still remaining in the first region 301 of the geotextile.. In the same or other embodiments, the second region 302 functions as a drainage and support region of the geotextile.

Another advantage of the system of figure 6 in contrast to the prior art arrangement of figure 1, is the reduction of the number of layers that need to be installed. Further, the method of producing the geotextile 300 of the present invention allows units of greater area to be produced and so a reduced number of units need to be transported to the installation site of the green roof system. Related to how easy the geotextile is to install, in embodiments such as that shown in figure 6, and in others, the basis weight of the geotextile (i.e. weight per unit area) is selected to be between 400 g/m2 and 2000 g/m2. In the same or other embodiments, the basis weight of the geotextile is selected to fall within the range 800 g/m2 and 1200 g/m2.

The geotextile 300, as discussed above, is utilised as a water retaining and draining layer. The water will eventually slowly flow from the geotextile and the roof module, and the resulting flow would be accelerated by an increased weight above the geotextile (such as that provided by excess water build up). In the meantime however, this temporarily retained liquid may be utilised by the growing plants and or seeds inside the green roofing system.

The impeded flow of water from the geotextile to the ground may also be of significant benefit to the drainage system, as described earlier.

The inter-fibre gaps may also give the textile filtering properties, and so the geotextile 300 is utilised as a filter layer. Solid particles larger than the inter-fibre gaps are unable to pass between the fibres and through the textile. Because the textile is liquid permeable, such solids are effectively filtered from the liquid. A geotextile according to the present invention may have a growing medium placed atop it that may include solids, for example soil, aggregate, and/or other fine particles. The textile material inhibits the passage of soil and/or aggregate from the inside of the roofing module to the outside of the roofing module, filtering it from any liquids. Such filtering may reduce the depletion of the soil and plant nutrients from the green roofing system through being washed away by water flow, thereby reducing soil replenishment requirements during the lifetime of the green roofing system.

Figure 7 is a cross-sectional view of an alternative embodiment of the invention, being a nonwoven geotextile mat 700. As with the embodiment shown in figure 3, there exists a first region 701 of the geotextile mat 700 being formed of fibres 401, and having a first average inter-fibre separation 'x'. There is also, as in figure 3, a second region 703 of the geotextile mat 700 being formed of fibres 501, and having a second average inter-fibre separation 'y'. In similar manner to the embodiment shown in figure 3, the two regions 701, 703 are connected via a graduated transition 702. However, in this embodiment the graduated transition 702 is present in only a part of the cross-section of the geotextile mat 700, so that there are clearly distinct first and second regions 701, 703. In contrast, in the embodiment of figure 3 there is a less distinct boundary between the first and second regions.

It is also possible to provide substantially no graduation between the inter-fibre separations of the first and second regions, such that there exists an abrupt interface between the inter-fibre separation of the first region and the inter-fibre separation of the second region.

In manufacturing a geotextile mat according to the present invention, the fibres forming the mat may be combined and mixed in a carding process. Carding produces a tenuous, generally sheet-like, web of fibres. One way to produce the first and second regions having different average inter-fibre separations, may involve dividing the hopper of the carding machine into two regions using a 'fin' like panel to enable fibres to be fed into the carding machine either side of this panel. Thus as fibres are fed into the carding machine either side of this panel, a portion of the fibres on one side are blended into a portion of the fibres on the other side during the carding process to form a geotextile according to the present invention. The difference between the average inter-fibre separation of each region 301, 302 can be achieved in a number of ways.

For example, as discussed above, fibres of a first diameter may be fed into one region of the hopper whilst fibres of a second diameter may be fed into a second region of the hopper on the opposite side of the dividing panel. The fibres having the first diameter, being fed into one region of the hopper, form a web of fibres which will become the first region 301. Similarly, the fibres having the second diameter, being fed into the second region of the hopper, form a web of fibres which will become the second region 302. In being processed through the carding machine, a portion of the fibres having the first diameter are blended into a portion of the fibres having the second diameter. This blending gives rise to the graduation between the first and second regions 301,302.

To form the geotextile discussed in figure 7, or indeed any of the geotextiles discussed as being embodiments of the present invention, the web produced by the carding process described above may be subjected to a process of "needle-punching". The needle-punching process involves pushing a plurality of barbed needles through the web of fibres. The needles and the barbs thereon, push and pull fibres substantially past one another in the web, and generally through the sheet-like fibre web. These pushed and pulled fibres provide cross-links substantially through the fibre web, thereby mechanically interlocking the fibres, thereby increasing strength. Furthermore, during the needle-punching process, the web of fibres is compressed and the textile is therefore thinner and denser than its foregoing fibre web. This process can also be used to determine the average inter-fibre separation of a geotextile.

There are alternatives to needle-punching, for example a plurality of core-sheath bicomponent fibres can be included in the fibre web. These fibres have an inner core of a first polymer with a first melting point, and an outer sheath of a second polymer with a second melting point, the second melting point being lower than the first melting point.

After needle-punching, the nonwoven web may be subjected to a so-called convection-air-through bonding process in which the web is passed through a convection oven, during which the web is moved through several zones in which hot air is blown through the web. In this manner the low melt fibres are melted, before the web is then passed through a cooling zone such that the fibres become permanently bonded to one another.

Alternatively, heat may be applied via a calender roll to the textile web, whereupon the material of the outer sheath of the bi-component fibres melts. The melted outer sheaths of adjacent bi-components fibres then fuse with one another, becoming permanently fused upon cooling. In this way, at least some of the fibres of the nonwoven textile may be fused to one another, forming an interconnected matrix of fibres and increasing the rigidity and strength of the textile.

An alternative to using a heated calender roll to bond the fibre web may be point bonding. In this case, the calender roll may be embossed with a pattern. When heat is applied to the fibre web via such a calender roll the embossing pattern is imprinted into the nonwoven fabric, bonding the fabric according to the pattern on the roll. Again, pressure and/or heat is applied to the fabric web by calender rollers in the embossed region, causing melting of at least some of the fibres in the web. These melted fibres then fuse with one another, becoming permanently fused upon cooling.

Alternatively, the fibres of the nonwoven textile may be fused to one another by a binder agent. A binder agent may be applied wet to the fibre web, or to the fibres themselves before the fibres are formed into the fibre web. A binder agent could alternatively be applied to the fibres after the fibre web has been formed. Subsequently, the binder agent may be allowed to dry, thereby fusing at least some of the constituent fibres to one another. A suitable binder agent may be synthetic, for example synthetic glues or latex, acetates, or synthetic resins. Alternatively, a suitable binder may be naturally occurring, for example natural glues or latex.

There are of course other suitable methods of bonding nonwoven textiles as are known in the art. For example, ultrasonic bonding in which rapidly alternating compressive forces causes stresses in the textile which in turn cause heating and melting of at least some of the fibres. These fibres melt and fuse with one another, becoming permanently fused after the removal of the ultrasonic source, and subsequent cooling of the fibres.

Finally it may be suitable to include a mixture of the above bonding methods, for example the use of needle-punching and calendering, depending on the required properties of the geotextile.

Whilst the present invention has been described above with reference to specific examples and embodiments, it is to be appreciated that various changes or modifications could be made without departing from the scope of the claimed invention. For example, it is envisaged that in some embodiments and for certain applications it might be appropriate to coat or otherwise treat the fibres of the geotextile with chemicals such as wetting agents or ultra-violet absorbers. It is also possible for the fibres of the geotextile to container fillers such as ultra-violet absorbers or colour bodies. And of course, the fibres may simply be white, or any other convenient colour depending on the particular application or installation in which the geotextile is to be used.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or integers.

The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

Claims

CLAIMS1. A nonwoven geotextile (300) for use in a green roof, the geotextile (300) being formed as a unitary mat comprising a plurality of fibres, and characterized in that in cross-section it has: a first region (301) having a first average inter-fibre separation; and a second region (302) having a second average inter-fibre separation; wherein the second inter-fibre separation is greater than the first inter-fibre io separation.
2. The geotextile according to claim 1, wherein the first region has a first number of fibres per unit volume and the second region has a second number of fibres per unit volume, wherein the first number of fibres per unit volume is different to the second is number of fibres per unit volume.
3. The geotextile according to claim 2, wherein the first number of fibres per unit volume is larger than the second number of fibres per unit volume.
4. A geotextile according to claim 1, having a graduated transition (303, 702) in inter-fibre separation between said first and second regions.
5. A geotextile according to claim 4 wherein the graduated transition (303) is through the whole cross-section of the geotextile.
6. A geotextile according to claim 4 wherein the graduated transition (702) is present through a part of the cross-section of the geotextile between the first region and the second region.
7. A geotextile according to claim 1 having an abrupt interface in inter-fibre separation between the first inter-fibre separation of the first region and the second inter-fibre separation of the second region.
8. A geotextile according to any preceding claim wherein the fibres are selected from: io round cross section fibres, hydrophilic fibres, bi-component fibres, multilobal fibres, or any combination thereof.
9. A geotextile according to any preceding claim wherein 30% by weight of the fibres in the geotextile are bi-component fibres. 15
10. A geotextile according to claims 8 or 9 wherein the bi-component fibres include an inner core and an outer sheath, the sheaths of said bi-component fibres being fused to one another.
11. A geotextile according to claim 10 wherein said inner core of said bi-component fibre has a first melting point, and said outer sheath of said bi-component fibre has a second melting point, the second melting point being lower than the first melting point.
12. A geotextile according to any preceding claim wherein 35% by weight of the fibres in the geotextile comprise the first region.
13. A geotextile according to any preceding claim wherein 35% by weight of the fibres in the geotextile comprise the second region.
14. A geotextile according to any preceding claim wherein the fibres within the first region are multi-lobal fibres, hydrophilic fibres, or round cross-section fibres.io 15. A geotextile according to any preceding claim wherein the fibres within the second region are round cross-section fibres.16. A geotextile according to any preceding claim having an uncompressed thickness within the range 5mm and 50mm, 17. A geotextile according to any preceding claim having an uncompressed thickness within the range 25mm and 35mm.18. A geotextile according to any preceding claim wherein the first region comprises fibre having a linear mass density within the range of 0.1 decitex -20 decitex.19. A geotextile according to any preceding claim wherein the second region comprises fibre having a linear mass density within the range of 40 decitex -300 decitex.20. A geotextile according to any preceding claim having a basis weight selected from the range 400 -2000 g/m2.21. A geotextile according to any preceding claim having a basis weight selected from the range 800 -1200 g/m2.22. A geotextile according to any preceding claim wherein the first region is a water retaining and distribution region of the geotextile.23. A geotextile according to any preceding claim wherein the second region is a drainage and support region of the geotextile.24. A geotextile according to any preceding claim wherein the fibres are polymeric fibres, and at least some of the fibres are fused to one another.25. A geotextile according to any preceding claim installed within a green roof structure.26. A geotextile according to claim 25 wherein the geotextile is installed between a growth substrate layer and an underlying roof structure.27. A geotextile according to claim 26 wherein the geotextile is installed between the growth substrate layer and an insulation layer.28. A geotextile according to claim 27 as dependent on claims 22 and 23, wherein the water retaining and distribution region of the geotextile is adjacent to the growth substrate.29. A geotextile according to claim 27 as dependent on claims 22 and 23, wherein the drainage and support region of the geotextile is adjacent to the insulation layer.30. A geotextile according to any preceding claims, wherein said plurality of fibres comprise natural fibres.31. A geotextile substantially described herein with reference to the description and io Figures 3 -7.32. A geotextile as installed in a green roof substantially described herein with reference to the description and Figures 3 -7.Amendments to the claims have been filed as followsCLAIMS1. A nonwoven geotextile (300) for use in a green roof, the geotextile (300) being formed as a unitary mat comprising a plurality of fibres, and characterized in that in cross-section it has: a first region (301) having a first average inter-fibre separation and defining a first surface of the mat; and a second region (302) having a second average inter-fibre separation and defining a second surface of the mat; wherein the second inter-fibre separation is greater than the first inter-fibre separation.2. The geotextile according to claim 1, wherein the first region has a first number of fibres per unit volume and the second region has a second number of fibres per unit CO volume, wherein the first number of fibres per unit volume is different to the second number of fibres per unit volume. Cn3. The geotextile according to claim 2, wherein the first number of fibres per unit volume is larger than the second number of fibres per unit volume.4. A geotextile according to claim 1, having a graduated transition (303, 702) in inter-fibre separation between said first and second regions.5. A geotextile according to claim 4 wherein the graduated transition (303) is through the whole cross-section of the geotextile.6. A geotextile according to claim 4 wherein the graduated transition (702) is present through a part of the cross-section of the geotextile between the first region and the second region.7. A geotextile according to claim 1 having an abrupt interface in inter-fibre separation between the first inter-fibre separation of the first region and the second inter-fibre separation of the second region.8. A geotextile according to any preceding claim wherein the fibres are selected from: round cross section fibres, hydrophilic fibres, bi-component fibres, multilobal fibres, or any combination thereof.9. A geotextile according to any preceding claim wherein 30% by weight of the fibres in the geotextile are bi-component fibres.LO 10. A geotextile according to claims 8 or 9 wherein the bi-component fibres include an inner core and an outer sheath, the sheaths of said bi-component fibres being fused to one another.CDOCO11. A geotextile according to claim 10 wherein said inner core of said bi-component fibre has a first melting point, and said outer sheath of said bi-component fibre has a second melting point, the second melting point being lower than the first melting point.12. A geotextile according to any preceding claim wherein 35% by weight of the fibres in the geotextile comprise the first region.13. A geotextile according to any preceding claim wherein 35% by weight of the fibres in the geotextile comprise the second region.14. A geotextile according to any preceding claim wherein the fibres within the first region are multi-lobal fibres, hydrophilic fibres, or round cross-section fibres.
15. A geotextile according to any preceding claim wherein the fibres within the second region are round cross-section fibres.LO
16. A geotextile according to any preceding claim having an uncompressed thickness within the range 5mm and 50mm, CD
17. A geotextile according to any preceding claim having an uncompressed thicknessOCOwithin the range 25mm and 35mm.
18. A geotextile according to any preceding claim wherein the first region comprises fibre having a linear mass density within the range of 0.1 decitex -20 decitex.
19. A geotextile according to any preceding claim wherein the second region comprises fibre having a linear mass density within the range of 40 decitex -300 decitex.
20. A geotextile according to any preceding claim having a basis weight selected from the range 400 -2000 g/m2.
21. A geotextile according to any preceding claim having a basis weight selected from the range 800 -1200 g/m2.
22. A geotextile according to any preceding claim wherein the first region is a water retaining and distribution region of the geotextile.
23. A geotextile according to any preceding claim wherein the second region is a drainage and support region of the geotextile.LOCDOCO24. A geotextile according to any preceding claim wherein the fibres are polymeric fibres, and at least some of the fibres are fused to one another.25. A geotextile according to any preceding claim installed within a green roof structure.26. A geotextile according to claim 25 wherein the geotextile is installed between a growth substrate layer and an underlying roof structure.27. A geotextile according to claim 26 wherein the geotextile is installed between the growth substrate layer and an insulation layer.28. A geotextile according to claim 27 as dependent on claims 22 and 23, wherein the water retaining and distribution region of the geotextile is adjacent to the growth substrate.29. A geotextile according to claim 27 as dependent on claims 22 and 23, wherein the drainage and support region of the geotextile is adjacent to the insulation layer.30. A geotextile according to any preceding claims, wherein said plurality of fibres comprise natural fibres.31. A geotextile substantially described herein with reference to the description and Figures 3 -7.32. A geotextile as installed in a green roof substantially described herein with referenceto the description and Figures 3 -7.CD