GB2236775A

GB2236775A - Roof ventilator, e.g. for mono-pitch roof

Info

Publication number: GB2236775A
Application number: GB9019147A
Authority: GB
Inventors: George Molyneux
Original assignee: Radway Plastics Ltd
Current assignee: Radway Plastics Ltd
Priority date: 1989-09-07
Filing date: 1990-09-03
Publication date: 1991-04-17
Anticipated expiration: 2010-09-03
Also published as: GB8920242D0; GB2236775B; GB9019147D0

Abstract

A roof ventilator 70 intended to be used particularly near to the top of a mono pitch roof is made in the form of a plastics extrusion. It has a hollow box section which rests on the top course of slates or tiles 130, with an air inlet arrangement 88 along its lower edge 86 and an air outlet arrangement on its underside 96 at or adjacent to its upper edge 108. The extension has one or more formations 100 on its underside, whereby it is adapted to be attached to the slates or tiles of the roof, e.g. by embedding in mortar 136. Mortar pointing 138 is overlaid by conventional lead flashing which overlies surface 78 and is tucked into the groove between surfaces 78, 76. Baffles 80, 98, provide a sinuous air-flow path. <IMAGE>

Description

A Roof Ventilator The invention is concerned with roof ventilation, particularly in mono pitch roofs, that is to say roofs which have a single pitch or plane where the top edge of the roof terminates by abutting or overlying a wall.

Whereas in the case of the conventional duo pitch roof, the ventilation should permit free airflow from the eaves at one side of the building to the eaves at the other side, it is required with a mono pitch roof to provide for free airflow from the eaves to ventilation at or adjacent the ridge or wall against which the roof abuts.

There are difficulties in providing ventilation at the top end of a mono pitch roof, especially if flashing is used, as is generally the case, where the roof abuts a wall. On the other hand, if the ventilation is provided below any flashing, then there is a part of the roof void above the ventilation which is not properly vented.

It is the object of the invention to provide a roof ventilator which deals with the problems of providing ventilation at the top end of a mono pitch roof. The invention also includes roof structures utilising the ventilator.

According to a first aspect of this invention a roof ventilator comprises a strip of water-resistant, moisture impermeable material, the cross-section of which is such that the strip provides a hollow box element with an air inlet arrangement at or adjacent to one longitudinal edge and an air outlet arranged on its underside at or adjacent to its other longitudinal edge, the strip having one or more formations on its underside, whereby it is adapted to be attached to roof slates or tiles.

Preferably, the air inlet arrangement comprises a slot or slots formed through a wall of the box element which wall is so arranged that it is upstanding from the slates or tiles when the strip is attached to the slates or tiles. It is further preferred that the air outlet arrangement comprises a slot or slots opening through a bottom wall of the box element.

The air inlet arrangement may comprise a series of slots arranged end-to-end the series extending along substantially the entire end of the strip. The air outlet arrangement may comprise a similar series of slots, but alternatively, it may comprise an opening extending along substantially the entire length of the strip. In the latter case, the opening may be formed between a pair of downwardly depending flanges from the box element.

According to a preferred feature of the invention the attachment formation on the underside of the strip may comprise a downwardly depending "hook" formation along the air outlet edge of the strip, whereby the strip can be hooked over the top edges of a course of tiles or slates on a roof.

According to another preferred feature of the imnvention the attachment formation on the underside of the strip may comprise one or more undercut projections adapted to be anchored in mortar laid on the tiles or slates of a roof. For instance, there may be a series of two or more inverted T-section formations extending along the underside of the box element, the stem of each Tsection extending downwardly from the bottom wall of the box element and the cross piece of each T-formation providing a mortar key.

According to yet another preferred feature of the invention, the air outlet longitudinal edge of the strip is provided with one or more projecting lips adapted to engage in mortar pointing between that edge and a part of the roof structure. Each such lip may be a simple straight cross-section lip or it may have an undercut formation to assist in anchoring the strip to the mortar pointing.

In the preferred construction, there is a moisture barrier formation within the box element extending along the length of the strip, this moisture barrier being shaped to inhibit moisture fiow from the air inlet arrangement to the air outlet arrangement.

Preferably there is a moisture barrier upstanding from the bottom wall, but spaced from the top wall of the box element. There may also be a moisture barrier depending from the top wall but spaced from the bottom wall of the box element. It is further preferred that the upstanding and depending barriers are spaced from each other but overlapped in the vertical direction so that the airflow passage in the box element from the air inlet to the air outlet is sinuous. There may be a series of alternating upstanding and depending barriers.

According to another preferred feature of the invention a retaining cantilever flange is provided on the strip projecting in the opposite direction to the general air inlet to air outlet direction to provide a retaining edge around which flashing laid on top of the strip can be engaged. Such a retaining flange may be provided overhanging the wall of the box element in which the air inlet arrangement is formed. Alternatively, or additionally, such a retaining flange may be formed over a longitudinally extending recess in the top of the strip intermediate the air inlet and air outlet arrangements.

In one construction, the box element is generally of tapered cross-section so that it is wider at the air outlet edge than at the air inlet edge. In another construction, the box element is generally of rectangular cross-section. In yet another construction, the box element is of stepped cross-section rising from the air inlet edge to the air outlet edge.

The strip is preferably formed by an extrusion process, and it may be made in polyvinylchloride of a grade such as that used for the manufacture of plastics window frames, guttering and drain pipes.

According to yet another preferred feature of the invention the strip is fitted with a connector at one of its ends, the connector being of such a cross-section that it is a friction fit in the box element, part of the connector projecting from the strip for reception in the box section of an adjacent strip, whereby the two strips can be connected end-to-end. Preferably at least one end of the connector is closed, so that it can be used alternatively to close an end of the strip.

According to a second aspect of the invention a roof structural assembly includes a top course of slates or tiles and a ventilator in accordance with the first aspect of the invention laid on and attached to the top course of slates or tiles so that the air inlet arrangement is above the slates or tiles and the air outlet arrangement is above the top edge of the course of slates or tiles, the air outlet longitudinal edge abutting or being closely adjacent to a wall or a ridge tile of the structure, there being mortar infill between the air outlet edge of the strip and the wall or ridge tile.

In the preferred arrangement, a bed of mortar is laid on the top course of slates or tiles and the underside of the strip is laid on this bed, any projections on the underside of the strip being embedded in the mortar. If the structure comprises a mono pitch roof the top edge of which lies against the face of a wall, it it preferred to provide a flashing extending from the wall above the roof over at least part of the strip.

The invention will be better understood from the following description of the problems encountered in ventilating some types of roof, and various forms of the invention, which are described here by way of examples only, with reference to the accompanying drawings, in which: - Figure 1 is a section through a cavity wall of a building, showing the upper part of a "lean to" mono pitch roof of conventional construction, Figure 2 is a part perspective part section through a "lean to" roof employing undulating tiles and showing the fitting of a conventional roof ventilator, Figure 3 is a view similar to Figure 2, but showing the use of flat slates, the ventilator being omitted, Figure 4 is a section through a conventional mono pitch roof which overlies the top edge of a cavity wall showing the fitting of a ridge tile and a conventional ventilator, Figure 5 is a view similar to Figure 4, but showing the use of flat slates, Figure 6 is a transverse section through a roof ventilator in accordance with the first aspect of the invention, Figure 7 is a view looking in the direction of either of the arrows VII in Figure 6, Figure 8 is a perspective view showing the crosssection through an alternative form of roof ventilator in accordance with the invention, Figure 9 is a view similar to Figure 8 showing another alternative form of ventilator in accordance with the invention, Figure 10 is a section through part of a wall, with a "lean to" roof, showing the ventilator of Figure 6 in its location on the roof, but not actually secured, Figure 11 is a part section part perspective view of the roof detail shown in Figure 10, excepting that is also shows the method of securing the roof ventilator, Figure 12 is a view similar to Figure 11, but showing the fitting of a lead roof flashing, Figure 13 is another view similar to Figure 11, but to a smaller scale, and showing the completion of the ventilator detail including the flashing, Figure 14 shows an instantaneous cross-section and an end view of a connector, compared with the cross section of a ventilator of the type shown in Figure 6, with which the connector is to be used, Figure 15 is a front view of the connector shown in Figure 14, Figure 16 is an underneath view of the connector shown in Figure 14, Figure 17 is a perspective view showing the connector of Figures 14 to 16 fitted into one end of a ventilator of the type shown in Figure 6, Figure 18 shows a detail at the top end of a wall, where a mono pitch roof overlies the top of the wall, and a ventilator of the type shown in Figure 6 is employed, Figure 19 is a detail section through an alternative form of wall with a coping, showing a mono pitch roof employing a ventilator of the type shown in Figure 6, and Figure 20 is a section through a ventilator similar to that shown in Figure 6, excepting that it is formed with an integral soaker flashing.

Current Building Regulations in the United Kingdom, require certain roofs on buildings to have the void between the roof covering and the ceiling ventilated, in order to discourage condensation forming within the roof void and causing damage to roof timbers and their metal connectors, which are known as gang plates. The ventilation should be created in a manner such that it will create an actual airflow in the roof void; in the case of the conventional duo pitched roof this flow should be across the roof void from the eaves at one side of the building to the eaves at the other side; in the case of some roofs however, the airflow should be between lower and higher levels of the roof e.g. at the eaves and at the ridge.

In Figure 1 there is shown the detail at the junction between a conventional "lean to" roof 10 and a cavity wall comprising an inner leaf 12 and an outer leaf 14. The "lean to" roof is a typical example of a mono pitch roof where the problems which the invention is designed to tackle occur. A timber wall plate 16 is nailed to the wall, and the rafters 18 of the "lean to" roof abut the outer face of the wall plate 16, the rafters being secured to the wall plate. The position of the ceiling joists is indicated at 20.

A timber tile batten 22 is fixed across the top edges of the roof rafters 18, and each of the tiles 24 of a top course of roof tiles is hooked by a depending hook portion 26 onto the tile batten. This holds the top course of roof tiles in the correct location, where their top edges are very close to or abutting the outer face of the outer leaf 14 of the cavity wall.

The higher level intersection between the roof 10 and the outer leaf 14 has to be capable of preventing the ingress of water into the roof void, and the most common method of achieving this is to fit a lead soaker flashing 28, part of which extends over the top part of each of the top course of roof tiles 24, the other part extending up the outer surface of the wall 14 above the top edge of the roof, and being doubled over at the top. The waterproofing is completed by a lead cap flashing 30, part of which is set in the mortar between two courses of bricks above the top edge of the soaker flashing 28, the remainder extending downwardly over part of the soaker flashing which rests against the outer leaf 14 of the wall.

Figure 2 illustrates an arrangement very similar to that shown in Figure 1, and it shows the use of conventional undulating tiles 24. The fitting of the flashing 28 and 30 is a very time consuming process, in particular, because the plumber who fits the soaker flashing is required to "beat" the lead flashing to the undulating profile of the tiles. Of course, this leaves a somewhat unsightly lead flashing extending over the top marginal portions of the tiles, and besides being very labour intensive, it can easily result in cracks appearing in the lead causing water to enter the roof space. Moreover, severe weather conditions can result in the lead flashing lifting away from the top surface of the tiles, again permitting water to enter the roof void.

It will be apparent, that with the conventional construction illustrated in Figures 1 and 2, it is difficult to fit high level roof void ventilation, and as illustrated in Figure 2, this is usually achieved by perforating the roof covering and fitting a series of individual roof vents 32. It is not necessary to describe these vents in detail, because they do not form part of the present invention. However, current Building Regulations are that in the case of a single pitch roof, the roof vents are of such size and numbers, that the ventilation area they provide is equal to a continuous 5 millimetres wide air gap along the full length of the roof/wall intersection.However, whilst the current British Standard 5250 (which supplements the Building Regulations concerning roof void ventilation) clearly allows the fitting of vents through the roof as illustrated at 32 in Figure 2, it makes it clear that the use of individual vents must not result in local stagnant pockets of air in the roof void. In order to comply with this, it is not possible to use a small number of large ventilators, and therefore the builder has to fit a larger number of relatively small ventilators which, in the case of that illustrated in Figure 2 for instance, have to be fixed at 900 millimetres spacing to provide the required total ventilation gap.

Apart from the time and expense of fitting the individual ventilators 32, it will also be appreciated, that because these have to be fitted below the flashing, and generally in the course of tiles below the top course, there is still an appreciable void at the top of the roof, above the ventilator openings, which is not properly ventilated. Warm air may rise into this void and the moisture in it condense, and it is in this area that some of the important metal gang plates such as that illustrated at 34 in Figure 2 are used.

Figure 3 illustrates a lean to roof detail similar to that shown in Figure 2, excepting that instead of the undulating roof tiles, flat roof slates 36 are employed. However, it is still necessary to fit the flashing 28, and as a result, any roof vents such as that shown at 32 in Figure 2, have to be located well below the top of the roof structure.

In Figure 4, there is illustrated a conventional structure where a mono pitch roof 40 extends over the top of a cavity wall comprising an outer leaf 42 and inner leaf 44. In this construction, a timber roof plate 46 is fitted on top of the inner leaf 44, and the roof rafters 48 are secured to this roof plate. The battens extend to a position over the outer leaf 42, and ridge tiles 50 are secured by nails to a timber plate 52 secured across the upper ends of the rafters 48. The ridge tiles 50 have a downwardly curved portion 54 the lower edge of which overlies the top course of roof tiles 56. With this construction, mortar filling 58 is provided between the top sides of the roof tiles 56 and the curved portion 54 of the ridge tiles, but again any ventilation is provided by separate ventilators 60, which perforate the roof.It will be seen that as with the construction illustrated in Figure 2, the ventilators 60 have to be located well below the top end of the roof structure, so that this part of the roof void is not properly ventilated.

Figure 5 shows an arrangement similar to Figure 4, excepting that in this case, there is no cavity wall, and instead there are slates or tiles 62 secured to trusses 64 of the roof structure. Again, the ventilators 66 have to be fitted below the top of the roof structure.

Figure 5 also illustrates the use of flat slates instead of the tiles shown in Figure 4.

Turning now to Figure 6 and 7, there is illustrated a roof ventilator 70 which is made as a long length of extruded plastics material, such as unsaturated polyvinylchloride, of the grade used for the manufacture of plastics window frames, gutterings, drainpipes and the like. This material is of course water-resistant and moisture impermeable which is of value in building construction, and moreover, it is capable of being extruded, which distinguishes it from traditional building materials.The extrusion provides in effect a box element 72 having a flat bottom 74 and a top which is constituted by a lower portion 76, and an upper portion 78, which are parallel to each other, there being a downwardly depending wall or barrier 80 which joins the two top portions 76 and 78 so that there is a step at the position of the barrier element 80, the top portion 78 having a bottom flange 82 which extends over the upper marginal portion of the bottom portion 76, thus creating a deep channel 84 between the overlying flange 82 and part of the bottom portion 76.

At its bottom edge, the box element 72 is closed by a wall 86, but as is shown in Figure 7, after the extrusion has been formed, a series of rectangular slots or openings 88 is formed in the bottom wall 86, these openings 88 being arranged in end-to-end fashion, and separated from each other by relatively narrow struts 90.

At the top end of the box element 72, there is a vertical top wall 92, which descends to a position below the bottom 74 of the box element; the bottom 74 terminates short of the wall 92, and there is a parallel depending wall 94 at the top end of the bottom 74, the bottom ends of the parallel walls 92 and 94 being closed by an end wall 96. This end wall 96 is formed with rectangular slots in the same arrangement as that illustrated in Figure 7 for the end wall 86. In effect, the part of the box element consisting of the wall 94, the lower part of the wall 92 and the bottom wall 96 forms a hook depending from the main part of the box element 72, for a purpose which will hereinafter appear.

Within the box element, it will be noted that the barrier element 80 stops well clear of the bottom 74.

There is also an upstanding barrier element 98 spaced from the barrier element 80, the barrier element 98 being connected to the bottom 74 but spaced well clear of the top 78. It is to be noted that the lower part of the barrier 80 and the top part of the barrier 98 overlap each other in the vertical direction. It will already be apparent therefore, that there is an airflow path through the box element 72, entering through the slots 88 in the bottom wall 86, travelling upwardly along the interior of the box element (i.e. to the right as seen in Figure 6); circumventing the barriers 80 and 98 in a sinuous path, travelling upwardly through the upper part of the box element, and then downwardly through the hook portion, and out through the slots 88 formed in the end wall 96.

In addition, the extruded ventilator strip 70 has attachment means on the underside of the bottom wall 74, comprising a series of four inverted T-section strips 100; an L-shaped strip 102 one wall of which is in extension of the front face of the wall 86, and a straight strip or lip 106 extending downwardly from the front face of the wall 94. The horizontal flange of the strip 102 and the flange 106 are in the same horizontal plane as the cross pieces of the T-strips 100. It is to be noted that the top portion 78 of the top wall projects at 108 beyond the top face of the end wall 92, and in addition, there is a rib 110 projecting from the top face of the wall 92. Finally, a series of three small ribs 112 projects from the top face of the bottom portion 76 of the top wall within the channel 84.

By way of illustration only, the length of the box element 72 between its bottom wall 86 and the top wall 92 may be 150 millimetres, the depth of the box section measured from the top of the lip 108 to the bottom wall 96 may be 50 millimetres, and also in a typical example, each of the slots 88 in the walls 86 and 96 may be 15 millimetres wide and 8 millimetres deep.

Although it has been stated that the plastics extrusion will be made in long lengths, it is to be understood that the expression "long" relates to a comparison with traditional roofing elements such as tiles and slates, and there will be practical limitations to the length of strip which can be manipulated.

Typically, the sections may be supplied in lengths of 5 metres. It will be appreciated however, that it is possible to cut the strip to the length required on site.

The location of the ventilator strip provided by the invention in a typical "lean to" roof situation is illustrated in the detail shown at Figure 10. Part of the outer leaf 120 of a cavity wall is shown, and the "lean to" roof terminates against the outer face of the outer leaf 120. A timber wall plate 122 is nailed to the outer leaf 120 and the roof rafters, one of which shown at 124 extend upto and are secured to the wall plate 122. The usual sarking or roof felt 126 is fitted over the rafters 124, and a tile batten 128 is then nailed to the rafters 124, in a position where it projects above the top ends of the rafters as shown in Figure 10. A top course of roof tiles one of which is shown at 130 is hooked over the tile batten 128 by means of the depending ribs 132 provided along the top edges of the tiles. All this is conventional, excepting that the gap 134 between the top edges of the top course of tiles 130 and the outer face of the outer leaf 120 of the cavity wall may be somewhat wider than in a conventional construction.

The extruded strip 70 is placed on top of the top course of tiles 130, with its hook portion provided by the walls 92 and 94 abutting against the top edges of the tiles. Consequently, the extruded strip 70 is retained in this position, in exactly the same manner that a course of tiles is retained on the tile batten 128, or in the case of lower courses, on similar tile battens (see for example Figures 4 and 5). Therefore, the major portion of the extruded ventilator strip 70 overlies the top part of the top course of tiles 130, and the corner at the junction of the walls 92 and 96 touches or is in juxtaposition with the outer face of the outer leaf 120 of the cavity wall. It will also be seen, that the wall 92 forms a V-shaped cavity between the outer face of the wall and the wall 92 at the top end of the ventilator strip 70.It will be appreciated, that the strip 70 will be laid along the top of a number of tiles arranged endto-end.

Figure 11 shows the actual detail of the ventilator strip, when it has been .completely fitted.

Once the top course of tiles 130 has been hooked onto the tile batten 128, a layer of mortar 136 is applied over the portion of the tiles which will be covered by the ventilator strip. This layer of mortar must also fill the undulations in the tiles - if any - and leave a substantial thickness of mortar projecting above the tops of the tiles.

The strip 70 is then lowered into the position shown in Figure 10, and pressed downwardly, so that the anchoring strips 100, 102 and 106 become embedded in the mortar as is clear in Figure 11. It will be appreciated, that the mortar flows to the top sides of the horizontal flanges of these strips, and consequently, when the mortar sets, the strip 70 becomes firmly achored to that mortar. The mortar will naturally adhere to the tiles 130, and therefore the ventilator strip 70 is effectively anchored to all the tiles 130 of the top course over which it extends. Finally, mortar pointing 138 is applied in the gap between the outer face of the outer leaf 120 and the wall 92 at the top end of the ventilator strip.

This mortar pointing fills the gap and becomes anchored to the ventilator by virtue of the flange 108 and the rib 110.

Figure 12 shows the next stage of fitting during which a conventional lead soaker flashing 140 is laid against the outer surface of the outer leaf 120 above the extruded ventilator strip 70, and part of the soaker flashing is then laid over the top portion 78 of the top wall of the box element 72. Along its bottom edge, the soaker flashing 140 is turned around the bottom edge of the flange 82 and turned back into the channel 84, where it can be wedged if necessary, with lead wedges 142.

Figure 13 shows how the detail is completed, by the fitting of the conventional capped flashing 144, part of which enters the mortar between two courses of the outer leaf 120 of the cavity wall.

When the ventilator strip 70 is thus fitted, it completes the joint between the sloping tiled "lean to" roof and the cavity wall against which the roof abuts.

Moreover, it provides the essential roof top vent, because as previously explained there is an airflow path through the inlet holes 88, thence through the interior of the box element 72, and out through the outlet holes 88 in the wall 96. It is to be noted, that this outlet hole arrangement is at the very apex of the roof void, so that there -are no stagnant areas above the vent outlet within the roof void. Consequently, the ventilator provided by the invention is more effective than the conventional ventilation arrangements for mono pitch roofs such as those illustrated in Figure 2, 4 and 5.

Moreover, even with the relatively small inlet and outlet holes 88, there is an adequate ventilation which complies with current United Kingdom Building Regulations, because the holes are provided along the entire length of the roof. There are however some subsidiary advantages.

The first of these is that there is an appreciable saving in the width of the lead required for the soaker flashing 140. Because the ventilator itself is made of waterresistant and moisture impermeable material, it constitutes part of the effective flashing, so that the lead soaker flashing 140 only has to be brought down to the position where it is tucked into the channel 84, whereas in order to comply with Building Regulations, it would otherwise have to be brought over the tiles to approximately the same position as the lower end wall 86 of the ventilator strip. A considerable economy can be effected by reducing the amount of lead required for the flashing.Another advantage is because the bottom edge of the soaker flashing is tucked into the channel 84 (and if necessary secured there by wedges) there is no danger that the lower edge of the flashing will be lifted by strong winds, which is a common occurence with conventional flashing. A further advantage occurs if the roof is covered with profile tiles such as the undulating tiles illustrated in Figures 2 and 4. When this type of roof structure is used, the conventional lead flashing has to be beaten by the plumber to the profile of the tiles. This is not only time consuming, it frequently results in cracks being formed in the flashing, which in turn gives rise to damp problems in the roof void.Figure 13 actually shows the ventilator strip fitted to flat roof slates, but it will be appreciated that in the case of the profiled tiles, the mortar bed 136 has to fill the valleys of the undulations in the tiles, and provide a coat over the ridges of those tiles, since the attachment strips 100 must cross over the tops of the ridges. It should be mentioned, that costings show that this method of providing a top ventilation for a mono pitch roof will show great economy over the conventional method of venting, in addition to the improved venting by the avoidance of stagnant areas and areas within the roof void above the traditional roof vents.

Figures 14, 15 and 16 show a connector 150, which is useful for joining together two sections of the ventilator 70 in end-to-end fashion, and which can also be used for closing the ends of the ventilator strip. The connector 150 essentially comprises a relatively short length of plastics extrusion, made of the same material as the ventilator strip itself, this extrusion being illustrated at the top of Figure 14. One or both ends ot the extrusion are closed by an end plate 152 shown at the bottom of Figure 14.

It will be seen that the extruded part of the connector 150 has a top wall comprising a lower portion 154 and a an upper portion 156 joined by a channel section 158. In addition, it has a short vertical bottom wall 160 and a longer vertical top wall 162. The arrangement and dimensions of all these walls are such, that the extruded section can slide into the boxed section 72 of the ventilator, with its various walls in frictional contact with the insides of the walls 86, 76, 78 and 92 of the ventilator strip. The channel portion 158 of the connector extrusion accomodates the barrier 80 within the ventilator strip. It will be seen that the closure plate 152 is profiled so that it fits into the end of the ventilator strip 70, and indeed in end view, it follows exactly the same outline as the interior cross-section of the ventilator strip.

Reference to Figure 15 shows that there are two large cut-outs 164 in the front wall 160 of the connector extrusion, leaving only end portions and a central divider portion 166.

When it is required to connect two lengths of the ventilator strip together end-to-end (and of course the joint must be watertight) then approximately one half of the connector extrusion 150 is pushed into the end of one of the ventilator strips. It is located by holding it through one of the holes 88 in the bottom wall 86 of the ventilator strip into which it has been pushed, so that only part of the central pillar 166 enters that strip.

The then projecting part of the connector 150 is then introduced into the end of the other length of ventilator strip, until the ends of the two ventilator strips abut each other. In this position therefore, the extrusion of the connector provides a watertight connection between the ends of the two ventilator strips, and because the interior of the extruded connector is open, there is a free flow of air through it. Moreover, the large cut-outs 164 in the wall 160 of the connector align with two or more of the inlet holes 88 in the bottom wall 86 of each of the two ventilator strips which have thus been joined together.

Where the connector extrusion is used to close the end of a ventilator strip 70, the end wall 152 is secured to the end of the extrusion 150 using plastics adhesive, and therefore, when the extrusion is pushed into the end of the ventilator strip, the end plate 152 (the outside dimensions of which coincide with the interior dimensions of the box element 72) completely fills the end of the box element. The fitting of the connector with the end plate 152 into one end of a length of the ventilator strip 70 is illustrated in Figure 17.

This figure also shows the correct location of the connector, with one half of its length located inside one of the lengths of ventilator strip, ready to receive the end of the other ventilator strip.

Although the connector 150 is described as a relatively short length of plastics extrusion, it will be appreciated that it could also be manufactured in the form of a plastics injection moulding.

Turning now to Figure 18, there is shown a structural detail where a mono pitch roof 170 rests on top of a wall 172. When this type of structure is employed, a special form of ridge tile illustrated at 174 is used. The ridge tile has a vertical part 176 and an arcuate or bull-nosed part 178 which overlies the top edge of the roof structure. In this construction, the rafters 180 of the roof rest on the outer leaf of the wall 172, and on a wall plate 182 fastened to the top of the inner leaf of the wall. In addition, a second wallplate 184 is attached to the top ends of the rafters 180 over the outer leaf 172, and the vertical parts 176 of the ridge tiles 174 are nailed to the second wallplate 184.

The usual sarking 186 is laid across the rafters 180, and a tile batten 188 is stretched across the top ends of the rafters 180. The tiles or slates 190 of the mono pitch roof are hooked to the tile batten 188 in the conventional manner. After that, the ventilator strip 70 is fitted to the top course of slates or tiles, in the same manner as previously described, so as to provide ventilation at the apex of the roof void. Before the ridge tiles 174 are secured in position, mortar 192 is applied to the top wall and the top end wall of the ventilator strip, so that after the ridge tile is fitted, it closes the gaps between that tile and the upper part of the ventilator strip as illustrated in Figure 18. It will be appreciated, that with this type of construction, no flashing is required.

Another cavity wall and mono pitch roof construction is illustrated in Figure 19. In this construction, the two leaves 194 and 196 of the cavity wall are topped by coping stones 198. The construction is quite similar to that shown in Figure 18, excepting that the rafters 200 of the roof in this case are shown resting on a wall plate 202 nailed to one of the leaves of the cavity wall. It will be appreciated however, that other arrangements for supporting the rafters of the roof are possible.

The ventilator strip 70 is fitted to the top course of slates or tiles 204 as previously described.

The construction is completed by a lead flashing 206 set in the mortar under the coping stone 198, laid across the top part of the ventilator strip, and tucked into the channel 84 in that strip.

An alternative construction of the ventilator strip is illustrated in Figure 8. Again, the strip 210 is formed as a plastics extrusion, and it may be made in unsaturated polyvinylchloride of the grade used for plastics windows, drainpipes, guttering and the like. In this construction, the extruded strip has a generally rectangular cross-section box element 212, having a bottom wall 214 constructed in the same manner as the bottom wall 86 in the example illustrated in Figure 6, and having ventilation inlet holes 216. At the top edge of the ventilator strip however, there are two parallel vertical walls 218 and 220, but these are not closed by an end wall, but the space between them is simply open at the bottom.This still provides for a free flow of air through the box element of the ventilator strip from the inlet holes 216 along the main rectangular portion of the box element, and then down and out through the space between the walls 218 and 220. The strip also has various features which are similar to features of the strip described with reference to Figure 6. For instance, there are attachment ribs 222, 224 and 226, which are similar to the ribs 102, 100 and 106, and there are attachment flanges or ribs 228, 230 and 232 on the top end wal] 222 of the extrusion, which perform the same functions as the equivalent flanges and ribs 108 and 110 on the ventilator strip 70 shown in Figure 6.

One of the main differences between the construction shown in Figure 8 and that in Figure 6, is that the bottom and top portions of the top wall of the box element are in the same plane, but there is a channel portion 234 between these two top wall portions, and there are lips 236 and 238 projecting from the bottom and top portions of the top wall over the channel 234. In addition, a T-section rib 240 stands up from the bottom of the channel 234 in the centre of the width of that channel, the cross piece of the T-rib being in the same plane as the top wall of the extrusion. Another difference from the previous construction is that the bottom portion of the top wall of the box element projects beyond the bottom wall 214 to provide a protective flange 242. Finally, there is an upstanding barrier wall 244 within the box element, which cooperates with the depending barrier provided by the channel formation in the top wall of the box element, in the same way that the barriers 80 and 98 co-operate, to provide a water barrier, so that any rain driven into the bottom part of the box element through the inlet holes 216, cannot reach the outlet formed between the walls 218 and 220.

The ventilator strip 210 illustrated in Figure 8, can be used in all the situations previously described in place of the ventilator strip 70. Moreover, it functions in exactly the same manner. However, it is possible to fit the soaker flashing (if such a flashing is used) over only the upper part of the top wall of the ventilator strip, tucking the lower edge of the flashing under the lip 238; alternatively, the flashing can be continued further down, to a position where it can be tucked under the bottom edge of the T-rib 240, or indeed it can be brought to the bottom edge of the ventilator strip, where it can be tucked under the flange 242. The alternative fixing position enable different widths of soaker flashing to be employed, for example, a steeply sloping roof does not require as wide a soaker flashing as does a shallow pitch roof.In addition, the flange 242 provides some weathering protection for the ventilation holes 216.

It will be appreciated, that the channel 234 of the arrangement shown in Figure 6, or the flange 242 of that arrangement, could be employed on a ventilator strip having a cross-section similar to that shown in Figure 6.

Figure 9 illustrates another alternative extruded ventilator strip, the general construction of which is similar to that of the strips previously described.

However, in this construction, the box element 250 has steps at 252 and 256 whilst the top wall of the box element has a step at 258. The arrangement of the air outlet at the top end is similar to that shown in Figure 8, that is to say there is simply an opening between two top walls 260 and 262.

Also, in this construction, there is a channel 264 in the top wall of the box, element, but the rib 240 is omitted, and instead, a deep flange 266 at the lower end of the upper portion of the top wall extends over approximately half the width of the channel 264. Again, the ventilator strip 250 can be fitted in any of the situations where the strip illustrated in Figure 6 could be employed. One of the advantages of the top channel construction, is that in the case of a ridge tile such as that shown in Figure 18, the mortar at 192 will flow into the channel, and will become keyed to the ventilator strip, by engagement under the cross piece ot the T-section rib 240 or the lips 236 and 238.

In Figure 20, there is illustrated a ventilator strip 270 which is the same cross-section as the strip shown in Figure 6, excepting that there is an additional wide extension flange 272 extending in upward continuation of the top wall 78 of the extrusion. A rebate or weakening groove 274 extends along the entire length of the extrusion, and therefore it is possible to turn the flange 272 through 900 from its original position, to that illustrated in Figure 20. In this condition, the ventilator strip 270 provides its own soaker flashing. The flange 272 is simply laid against the outer face of the outer leaf of the wall, and water collecting on the outer face of the flange 272 then runs down the top wall of the ventilator itself, in the same way that it would run down the top face of a soaker flashing made of lead.It will of course be necessary to close the top edge of the plastics soaker flange by means of a lead cap flashing, but this can be done in the conventional manner. Obviously, this construction is much cheaper than one which employs conventional lead flashing, because only the relatively narrow cap flashing has to be made in lead.

One of the additional advantages of the constructions shown in Figures 8 and 9 is that the undercut recesses or channels 234 or 264 in the top of the box element of the ventilator strip, will act as anti-capillary traps, that is to say they will help to prevent water migrating upwardly across the top surface of the ventilator and under any lead flashing.

Furthermore, if the lead flashing is hooked around the rib 238 or the lower edge of the cross piece of the T-rib 240, they also provide an area for the lead to expand into in hot weather, and this will assist in preventing buckling of the lead flashing. The advantage of the step 252 in the construction illustrated in Figure 9, is that it will largely conceal the underside mortar joint on the slates or tiles when the ventilator is viewed from the ground adjacent to the building. It will be appreciated, that the aspect of the ventilator strip which is seen from the ground is simply the bottom edge with its perforations, and as this is of quite shallow depth, the overall effect will be aesthetically pleasing.

Claims

1. A roof ventilator comprising a strip of water resistant, moisture impermeable material, the cross section of which is such that the strip provides a hollow box element with an air inlet arrangement at or adjacent to one longitudinal edge and an air outlet arranged on its underside at or adjacent to its other longitudinal edge, the strip having one or more formations on its underside, whereby it is adapted to be attached to roof slates or tiles.

2. A roof ventilator as claimed in Claim 1, in which the air inlet arrangement comprises a slot or slots formed through a wall of the box element, which wall is so arranged that it is upstanding from the slates or tiles when the strip is attached to the slates or tiles.

3. A roof ventilator as claimed in Claim 1 or Claim 2, in which the air outlet arrangement comprises a slot or slots opening through a bottom wall of the box element.

4. A roof ventilator as claimed in any one of Claims 1 to 3, in which the air inlet arrangement comprises a series of slots arranged end-to-end, the series extending along substantially the entire length of the strip.

5. A roof ventilator as claimed in any one of Claims 1 to 4, in which the air outlet arrangement comprises a series of slots arranged end-to-end, the series extending along substantially the entire length of the strip.

6. A roof ventilator as claimed in any one of Claims 1 to 4, in which the outlet arrangement comprises an opening extending along substantially the entire length of the strip.

7. A roof ventilator as claimed in Claim 6, in which the opening is formed between a pair of flanges depending downwardly from the box element.

8. A roof ventilator as claimed in any one of Claims 1 to 7, in which the attachment formation on the underside of the strip comprises a downwardly depending "hook" formation along the air outlet edge of the strip, whereby the strip can be hooked over the top edges of a course of tiles or slates on a roof.

9. A roof ventilator as claimed in any one of Claims 1 to 7, in which the attachment formation on the underside of the strip comprises one or more undercut projections adapted to be anchored in mortar laid on the tiles or slates of a roof.

10. A roof ventilator as claimed in Claim 9, in which each undercut projection comprises an inverted T section formation extending along the underside of the box element, the stem of the T-section extending downwardly from the bottom wall of the box element and the cross piece of the T-formation providing a mortar key.

11. A roof ventilator as claimed in any one of Claims 1 to 10, in which the air outlet longitudinal edge of the strip is provided with one or more projecting lips adapted to engage in mortar pointing between that edge and a part of the roof structure.

12. A roof ventilator as claimed in Claim 10, in which each lip is a simple straight cross-section lip.

13. A roof ventilator as claimed in Claim 10, in which each lip has an undercut formation to assist in anchoring the strip to the mortar pointing.

14. A roof ventilator as claimed in any one of Claims 1 to 13, in which there is a moisture barrier formation within the box element extending along the length of the strip, this moisture barrier being shaped to inhibit moisture flow from the air inlet arrangement to the air outlet arrangement.

15. A roof ventilator as claimed in Claim 14, in which the moisture barrier upstands from the bottom wall, but is spaced from the top wall of the box element.

16. A roof ventilator as claimed in Claim 15, in which there is also a moisture barrier depending from the top wall but spaced from the bottom wall of the box element.

17. A roof ventilator as claimed in Claim 16, in which the upstanding and depending barriers are spaced from each other but overlapped in the vertical direction so that the airflow passage in the box element from the air inlet to the air outlet is sinuous.

18. A roof ventilator as claimed in Claim 17, in which there is a series of alternating upstanding and depending barriers.

19. A roof ventilator as claimed in any one of Claims 1 to 18, in which a retaining cantilever flange is provided on the strip projecting in the opposite direction to the general air inlet to air outlet direction to provide a retaining edge around which flashing laid on top of the strip can be engaged.

20. A roof ventilator as claimed in Claim 19, in which the retaining flange overhangs the wall of the box element in which the air inlet arrangement is formed.

21. A roof ventilator as claimed in Claim 19, in which the retaining flange is formed over a longitudinally extending recess in the top of the strip intermediate the air inlet and air outlet arrangements.

22. A roof ventilator as claimed in any one of Claims 1 to 21, in which the box element is generally of tapered cross-section so that it is wider at the air outlet edge than at the air inlet edge.

23. A roof ventilator as claimed in any one of Claims 1 to 21, in which the box element is generally of rectangular cross-section.

24. A roof ventilator as claimed in any one of Claims 1 to 21, in which the box element is of stepped cross section rising from the air inlet edge to the air outlet edge.

25. A roof ventilator as claimed in any one of Claims 1 to 24, in which the strip is formed by an extrusion process.

26. A roof ventilator as claimed in Claim 25, in which the strip is made in polyvinylchloride of a grade such as that used for the manufacture of plastics window frames, guttering and drain pipes.

27. A roof ventilator as claimed in any one of Claims 1 to 26, in which the strip is fitted with a connector at one of its ends, the connector being of such a cross-section that it is a friction fit in the box element, part of the connector projecting from the strip for reception in the box section of an adjacent strip, whereby the two strips can be connected end to-end.

28. A roof ventilator as claimed in Claim 27, in which at least one end of the connector is closed, so that it can be used alternatively to close an end of the strip.

29. A roof ventilator constructed and arranged substantially as herein described with reference to Figures 6 and 7, or Figure 8 or Figure 9, or Figures 14, 15 and 16, or Figure 20 of the accompanying drawings.

30. A roof structural assembly which includes a top course of slates or tiles and a ventilator in accordance with any one of Claims 1 to 29 laid on and attached to the top course of slates or tiles so that the air inlet arrangement is above the slates or tiles and the air outlet arrangement is above the top edge of the course of slates or tiles, the air outlet longitudinal edge abutting or being closely adjacent to a wall or a ridge tile of the structure, there being mortar infill between the air outlet edge of the strip and the wall or ridge tile.

31. A roof structural assembly as claimed in Claim 30, in which a bed of mortar is laid on the top course of slates or tiles and the underside of the strip is laid on this bed, any projections on the underside of the strip being embedded in the mortar.

32. A roof structural assembly as claimed in Claim 30 or Claim 31, in which the roof is mono pitch, the top edge of the roof lying against the face of a wall, there being a flashing extending from the wall above the roof over at least part of the strip.

33. A roof structural assembly constructed and arranged substantially as herein described with reference to Figure 11; or Figure 13 or either of Figures 11 and 13 modified by Figures 15 and 16 or Figure 18 or Figure 19 of the accompanying drawings.