GB2030193A - A structural assembly comprising a damp-proof course - Google Patents

Abstract

The damp-proof course has a membrane 110 with a rib 114 along one longitudinal edge, the membrane being located between two structural elements 130, 138, and the damp-proof course extends across the full width of at least one of the two elements. The rib 114 provides a location along an edge of one of the structural elements. The damp-proof course may be made of extruded plastics material (e.g. polyethylene) and the rib may be of hollow cross-section. Structural assemblies include vertical damp-proof courses at the ends of cavity walls adjacent to the openings for doors and window frames, and horizontal damp- proof course are also described. <IMAGE>

Description

SPECIFICATION A structural assembly The present invention relates to structural assemblies which incorporate damp-proof courses. It is standard building practice in the United Kingdom and other countries, to provide a damp-proof course, usually in the form of a water-impermeable membrane, between structural elements. The term "structural elements" is used throughout this specification to describe any element which has a load bearing or a cladding or a supporting function in the building, and incudes for example, leaves of cavity walls, individual building bricks or blocks, timber, metal or plastics frames or parts of cast structures such as concrete walls.

Perhaps the most extensive use of a damp-proof course is as a horizontal moisture barrier in a wall between successive courses of building bricks or blocks, or as a similar horizontal moisture barrier in a solid concrete wall. In this position, the purpose of the damp-proof course is to prevent moisture rising through the relatively pervious materials from which the wall itself is constructed. In older buildings, the horizontal damp-proof course is made of slates, but for many years now, bitumen impregnated felt has been used. The felt-type damp-proof course is usually supplied in long lengths precutto the same width as the standard building brick, and if fitted properly provides a quite satisfactory moisture barrier. There are however a number of reasons why the fitting of a horizontal damp-proof course is frequently done incorrectly.

To begin with, the damp-proof course should extend across the full width of the structural element (i.e. the vertical wall) and sometimes it is specififed that the damp-proof course shall project on the outside of the wall. Now clearly if the felt is precut to the width of the bricks and some of it is left projecting on the outside of the wall, the inner edge of the felt must be displaced outwardly with respect to the wall, and therefore it is possible to form a moisture bridge across the inside edge of the felt, because mortar between the courses of bricks can flow around the inside edge. (The terms "indside" and "outside" refer to the outer leaf of a cavity wall for the inner leaf, these terms must be reversed.) It is in any case quite difficult to lay the felt damp-proof course so that its longitudinal edges coincide pre cisely with the edges or faces of the bricks, and there is always the possibility that at some position along the length of a wall, the felt will be so displaced that a mortar bridge can form.

However, perhaps the most serious problem of the known felt-type horizontal damp-proof course is that the outer edge is rarely left projecting (because it would be unsightly) and the bricklayer generally points over the outer edge with mortar, thus deliberately creating a mortar bridge through which moisture can travel upwardly. This is a very common cause of rising damp in buildings.

One of the objects of the present invention is to provide a structural assembly which may incorpo rate a horizontal damp-proof course, which is less prone to the faults previously mentioned.

Vertical damp-proof courses also have to be fitted in cavity walls where the cavity end is closed (e.g. at an opening formed to receive a door or window frame or where there is an end formed on a projecting wall) and again the bitumen impregnated felt strip is commonly used for this purpose. It is possible to employ a sepcially constructed dampproof course and cavity closer in many such positions, such as that described in the Specifications of United Kingdom Patents Nos: 1,302,694;1,302,695 and 1,302,696. Although such specialised cavity closers are being increasingly used, they are radically different from the flexible felt type damp-proof course and they require new building techniques, which some builders and bricklayers are reluctant to adopt.

Another object of the present invention therefore is to provide a structural assembly which may include a vertical damp-proof course and which can be built using almost unaltered conventional techniques.

According to this invention a structural assembly comprises first and second structural elements (as herein defined) arranged close to each other, and a damp-proof course having a memberane with a rib along one longitudinal edge, the membrane being located between the two structural elements and the damp-proof course extending across the full width of at least one of the two elements. Such an assembly can comprise a horizontal damp-proof course (in which case, the first and second structural elements are constituted by parts of the same wall or leaf of a wall) or it can comprise a vertical damp course (in which case, the first and second structural elements may be constituted by one leaf of a cavity wall and the ends of the end closure bricks or blocks, or the end of a wall and the stile of a window or door frame).It is to be understood however, that the invention is not confined to these two specific damp-proof course locations. The structure may for example include part of a wall and the stile or head of a window or door frame.

In the broadest aspect of the invention, as stated above, the only novelty resides in the provision of the rib along the longitudinal edge of the dampproof course membrane. However, this apparently simple expedient provides a means of overcoming some of the serious practical problems which arise in building, some of which have been mentioned above, and others of which will appear in the description of the specific embodiments hereinafter.

It is possible to locate the rib along an edge of a first of the two structural elements and this provides a method of correctly aligning the damp-proof course relatively to the structural elements. Furthermore, the engagement of the rib with a face of one of these elements ensures that part of the dampproof course (i.e. the rib itself) can be seen in the completed structure, thus ensuring that the dampproof course is properly fitted. There may be a second rib along the other longitudinal edge of the membrane, this second rib locating along an opposite edge of the first of the structural elements. This preferred arrangement ensures that there is a com plete alignment of the damp-proof course with the structural element, and is especially useful when the invention is used to provide a horizontal damp-proof course.

The or each rib may be of hollow cross-section, and in a preferred form of the invention, the rib is in the form of a tube of substantially circular crosssection. It is still further preferred, that the membrane extends tangentially to the circular crosssection of the rib, so that the rib projects only from one face of the membrane. With this preferred construction, the membrane can lie against a face of the first structural element, with the rib or ribs engaging against edge faces of that structural element, and mortar can then be applied to the face of the membrane opposite to that from which the rib(s) projects.In the case of a horizontal damp-proof course, it is thus possible for the outside of the mortar joint to be pointed, to give a finished appearance to the joint, whilst leaving the rib itself on the outside of the outer leaf of the wall, clearly visible, but at the same time presenting a detail of good appearance.

According to a preferred feature of the invention, at least one flange projects from the membrane at a position intermediate its ends, and is engaged with a face of one of the structural elements, at right angles to the face of that element which faces the other element. According to another preferred feature of the invention, the membrane is bent through a range angle so that a first part of it lies contiguous with one face of the first of the structural elements and the other part lies contiguous with an adjacent face of that element at right angles to the first face.

In some forms of the invention, there may be a third structural element, arranged in close juxtaposition to the first element, facing the said adjacent face of the first element, so that the said other part of the membrane is located between the first element and the third element, this other part of the membrane extending across the full width of one of the facing surfaces of the first and third elements.

The invention is particularly useful at the end of a cavity wall, where the frame of a window or door is to be fitted, and according to a preferred feature of the invention, a structural assembly comprises a cavity wall having inner and outer leaves, a stile, head or sill of a window or door frame arranged close adjacent to an end of the cavity wall, and a damp-proof course having a membrane located between the end of the one of the leaves of the wall and the stile, head or sill, the damp-proof course having a rib extending along one edge of the membrane and engaging in a corner formed between the said one leaf of the cavity wall and the stile, head or sill, and the damp course having a part bent through a right angle from the membrane at the opposite side of the stile, head or sill to the rib, so as to locate against either a face of the stile, head or sill or against a face of the said one leaf which is in the cavity. Whereas the oridinary damp-proof course which is fitted between the outer leaf of the wall and the closure bricks or blocks lies in a single plane, and the window or doorframe is frequenclyfitted so that it abuts the outer leaf of the wall, and therefore the frame is not protected from moisture in the outer leaf, in the preferred construction just outlined, the damp-proof course provides a moisture barrier between the end of the wall and the window or doorframe itself. This is particularly useful if the window or doorframe is made of timber which is subject to rotting, or metal which is subject to corrosion.In one instance, the part of the membrane which is bent at right angles lies against the inside face of the stile of the frame, and therefore provides a moisture barrier between the plaster which is generally applied to the inside reveal of the window or door opening and the frame, and in the other case, where it is bent into the cavity, it provides the usual cavity closure damp-proof course.

According to yet another preferred feature, there is a second part of the damp-proof course bent at right angles from the membrane in the opposite direction to the first bent part, so that one bent part locates on a face of the stile, head or sill and the other locates against a face of the said one leaf which is in the cavity. It will be appreciated that with this construction, the damp-proof course fulfills all three functions referred to in the preceding paragraph.

According to another preferred feature of the invention, a structural assembly comprises a cavity wall having inner and outer leaves, a stile, head or sill of a window or door frame arranged closely adjacent to an end of the cavity wall, there being closure means closing the end of the cavity and a damp-proof course which cmprises a membrane having a rib along one longitudinal edge, a first part of the membrane being located between the end of the cavity wall and the stile, hed or sill and extending completely across the joint between the stile, head or sill and the cavity wall, and a second part of the membrane bent at right angles to the first part and being located between the closure means and one of the leaves of the cavity wall, this second part of the membrane extending completely across the joint between the closure means and the leaf, the dampproof course also having a rib extending along a longitudinal edge of the membrane and located in the corner between the stile, head or sill and the end of the cavity wall. Preferably a second rib is formed along the other longitudinal edge of the membrane and rests against the face of the leaf of the wall which faces the closure means on the inside of the closure means. Aflange may project from the membrane and engage with the inner end face of the closure means.

According to yet another feature of the invention, the rib which engages in the corner between the stile, head or sill and the end of the cavity wall bridges any space between the stile, head or sill and the end of the cavity wall to form a water seal therebetween. In the conventional arrangement, it is always necessary to apply mastic sealing to the joint around the outside of a frame and the brick or blocks from which the wall is constructed. This is in an attempt to prevent ingress of moisture through the joint. Mastic pointing is an expensive operation one reason being that it has to be carried out after all other building operations except painting, have been completed, and this generally involves ladder or scaffolding work. Further, the application of the mastic pointing is a specialised job.However, if the rib of the damp-proof course is arranged as just described, then it replaces the mastic pointing, and as it is automatically fitted by the bricklayer during the building of the wall, the entire operation of mastic pointing can be obviated.

According to a still further preferred feature of the invention, there are one or more intermediate flanges projecting from the membrane of the dampproof course intermediate its rib and the right-angle bend, which flange or flanges engage(s) in mortar squeezed out from the leaf of the cavity wall against which it is located. In the case where the membrane is formed into a right-angle bend, there may be one or more intermediate flanges projecting from the membrane intermediate the right-angle bend and the end of the membrane which is located in the cavity.

According to a preferred feature of the invention, the damp-proof course is made in plastics material, and it is preferably so constructed, that the membrane is flexible. Hence, the damp-proof course which is used in the strutural assemblies in accordance with the invention, has physical characteristics closely resembling those of known damp-proof courses made of bitumen impregnated felt or plastics materials, and hence can be manipulated and fitted by the bricklayer in much the same way as he is used to fitting conventional damp-proof courses.

The damp-proof course may in fact be produced by an extrusion process.

Various constructions in accordance with the invention, will now be described by way of examples only, with reference to the accompanying drawings, in which :- Figure 1 is a horizontal cross-section through the end of a cavity wall adjacent to a window frame showing the conventional construction, Figure 2 is a perpsective view of the end of a cavity wall adjacent to a window or door frame opening, showing the conventional construction, Figure 3 is a detail perspective view of one of the courses illustrated in Figure 2, Figure 4 is a transverse section through a dampproof course in accordance with the invention, Figure 5 is a detail sectional view showing an alternative form of rib, Figure 6 is a view similar to Figure 5, but showing another form of rib, Figure 7shows in horizontal cross-section a structural assembly in accordance with the invention, where a timber window frame is fitted to the end of a cavity wall, Figure 8 is a view similar to Figure 7, but showing the fitting of a timber door frame to the end of a cavity wall, Figure 9 is a transverse section through an alternative form of damp-proof course, Figure 10 is a view similar to Figure 8, but showing the use of the damp-proof course illustrated in Figure 9, with a timber window frame, Figure 1 is a view similar to Figure 10, but showing the use of the damp-proof course with a timber door frame, Figure 12 is a vertical cross-section through a cavity wall of conventional cross-section, showing problems which can arise in fitting a horizontal damp-proof course, Figure 13 is a vertical section through a leaf of a cavity wall illustrating the use of a damp-proof course in accordance with the invention.

Figure 14 is a view similar to Figure 13, but illustrating an alternative use of the damp-proof course shown in Figure 13, Figure 15 is a view similar to Figure 13, but showing the use of a slightly modified form of damp-proof course, Figure 16 is a view similar to Figure 13, but showing a preferred damp-proof course, and Figure 17 is a vertical section through a cavity wall, over a timber window frame opening.

Referring to Figures 1,2 and 3 of the drawings, the outer leaf of a cavity wall is shown at 10, and the inner leaf at 12. For present purposes, it is assumed that both leaves of the wall are built from standard metric sized building bricks, and in accordance with standard building practice, there is a cavity 14 approximately 50 millimetres wide between the two leaves 10 and 12. At the end of the cavity wall, where there is an opening for a window frame (the stile of which is shown at 16) it is necessary to close the cavity end, so as to provide an end surface over which the plaster 18 of the inside reveal of the window opening can be applied.As illustrated in Figures 2 and 3, in order to close the end of the cavity, bricks have to be cut, to form three-quarter bricks 20 used in one course of the inside leaf 12, the quarter bricks 22, used on the succeeding course of the inside leaf 12. Thus, there is an end face indicated at 24 in Figure 1 - of the closure threequarter and quarter bricks, which is of the same width as a standard building brick, and which abuts the inside (cavity) face 26 of the outer leaf 10 of the wall. Since the purpose of the cavity is to prevent moisture travelling through the wall from the outside to the inside, it is clearly necessary to provide a moisture barrier between the outer leaf 10, and the closure bricks 20 and 22. In the conventional construction therefore, a bitumen impregnated felt strip 28 is laid vertically between the faces 24 and 26, during construction of the wall.Hence, there should be a complete moisture barrier provided by the the damp-proof course strip 28, between the outer leaf 10, and the inner leaf 12.

In practice, mortar squeezed out from between the courses of bricks sometimes bridges the inner longitudinal edge 30 of the damp-proof course 28, and since this is inside the cavity, it is not only inaccessible, but is also rarely observed. Any such mortar bridge across the inner edge of the dampproof course provides a potential moisture path from the outer leaf to them inner leaf of the wall, and this can result in damp patches appearing on the plaster work on the inside of the wall. If this happens, it is necessary to dismantle part of the wall, and re-build it correctly.

Referring to Figure 1, it will be seen that the stile 16 of the window frame is located so that it bridges the outer longitudinal edge of the damp-proof course 28, and extends just on to the closure bricks 20 and 22.

This is to ensure that the plaster 18 does not extend over the damp-proof course, to a position where it could be in contact with the outer leaf 10 of the wall, since that would provide another path for moisture from the outer leaf into the plaster 18.

Many architects consider it desirable to have a damp-proof course between the window frame and the end 32 of the outer leaf 10 of the wall, but such damp-proof courses are hardly ever fitted, except when using the special cavity closers described in the Specifications of Patent Nos: 1,302,694; 1,302,695 and 1,302,696. Consequently, the window frame is always exposed to the outer leaf 10, and this sometimes leads to deterioration of the frame. For completeness, it will be mentioned that the joint formedm between the end 32 of the outer leaf 10 and the stile 16 is covered on the outside by mastic pointing 34 which is applied in the corner formed by the outer leaf 10 and the outer face of the stile 16.

The purpose of the mastic pointing 34 is to prevent the ingress of moisture between the leaf 10 and the stile 16, but this does not deal with the problem created by the fact that the outer leaf 10 is frequently very damp, and moisture from that leaf can pass directly into the stile 16 if there is no damp-proof course provided between the wall and the frame.

Turning now to Figure 4, there is illustrated a special damp-proof course 40 which is extruded in long lengths, the cross-sectional shape of the extrusion being shown in Figure 4. It will be observed that the damp-proof course 40 comprises essentially a membrane 42, ribs 44 and 45 extending respectively along the longitudinal edges of the membrane 42. In addition, there is a series of flanges 46,48, 50, 52,54, 56,58,60,62,64,66 and 68 each of which extends outwardly from a respective face of the membrane 42. It will be observed from Figure 4, that these flanges are in fact arranged in pairs, such as 46 and 58, and that as the damp-proof course is extruded, some of these flanges are inclined towards one side of the membrane, and others towards the opposite side of the membrane.

The membrane 42 and the various flanges are all approximately 1 millimetre thick, but the ribs 44 and 45, which as illustrated in Figure 4, are of cylindrical tube form, are approximately 2.5 millimetres thick.

Hence, it will be appreciated that the damp-proof course 40 is generally quite flexible, and that the flanges can be folded flat against the membrane 42, or bent from the position which they occupy as extruded. Clearly, it is also possible to coil the damp-proof course 40 on itself as with conventional damp-proof courses, although the size of the coil will be governed by the outside diameter of the ribs 44 and 45, which effectively determined the overall thickness of the damp-proof course when it is coiled.

It will be appreciated, that during coiling, the flanges tend to be compressed towards the membrane 42.

By virtue of the extrusion method of manufacture, the damp-proof course can be produced quite cheaply. It must be made in a water impervious plastics material, and polyethylene of the type which is commonly used for damp-proof courses is quite adequate.

The spacing between some of the pairs of flanges is significant. Thus, between the roots of the flanges 48 and 60 on the one hand and the rib 44 on the other hand, there is a distance of approximately 70 milimetres, which corresponds to the width of the stile of a standard window frame as conventionally used in the United Kingdom. Similarly, the flanges 54 and 66 on the one hand and the rib 45 on the other hand are spaced by a distance equal to the width of a standard window frame stile. The distance between the roots of the flanges 50 and 62 on the one hand and the rib 44 on the other hand, is approximately 82 millimetres, that is to say it is equivalent to the width of the standard door frame stile used in the United Kingdom. Similarly the distance between the roots of the flanges 52 and 64 on the one hand and the rib 45 on the other hand is approximately 82 millimetres.The distance between the rib 44 and the roots of the flanges 46 and 58 is approximately 12 millimetres, and similarly the roots of the flanges 56 and 68 are spaced by 12 millimetres from the rib 45.

An important feature of the damp-proof course 40 is that it is entirely symmetrical about the plane of the membrane 42, and also about a plane perpendicular to the membrane 42, and passing through the damp-proof course along its longitudinal axis. This is a useful feature of the invention, because it means that no special precautions have to be taken in fitting the damp-proof course, since it is in no way handed.

Figure 7 illustrates the end of a cavity wall comprising an outer leaf 70 and an inner leaf 72, with a cavity 74 between them, the end of the cavity being closed by three-quarter bricks and quarter-bricks indicated at 76. The stile 78 of a standard timber window frame is shown applied to the end 80 of the outer leaf 70 of the wall, and it is to be noted that in this instance, the inside face of the stile 78 is in alignment with the inner face 82 of the outer leaf 70 (that is the face of the outer leaf which is in the cavity 74). Many builders would prefer this position for the window frame, because it allows the sill of the window frame to overhand the outer face of the outer leaf 70 by a slightly greater distance, than if the window frame is required to bridge the joint between the outer leaf 70, and the closure bricks 76.

The damp-proof course 40 which has been described with reference to Figure 4, is shown fitted between the stile 78 and the end face 80 of the outer leaf 70, and also between the inside face 82 of the outer leaf and the facing end of the closure bricks 76.

During construction of the building, when the courses of the wall reach the level at which the window frame can be fitted, a length of the dampproof course 40 equal to the total height of the window frame is cut off, and secured to the stile 78 and to the ends of the head and sill of the frame which form continuations of the end face of the stile 78, so that the entire end face of the frame is protected by part of the damp-proof course 40. The rib 44 is pressed against the outer face of the stile 78, and this provides a means of locating the dampproof course 40 relatively to the window frame, this in itself ensuring that fitting can be carried out neatly and accurately. The damp-proof course is secured to the stile 78 by nails 84 driven through the membrane 42 of the damp-proof course.The "free" edges of the flanges 46 and 58 will be splayed to some extend from the membrane 42, as is illustrated in Figure 7.

The flange 60 is located in such a position, that it can be bent at right angles to the portion of the membrane 42 which extends along the side of the stile 78, so that it locates on the inside face of the stile 78, where it can be secured by nails 86 driven into the stile. Now this not only ensures that the damp-proof course is effectively secured to the window frame, it also provides a moisture barrier, between the window frame, and the plaster 88, which is eventually applied inside the reveal of the window opening.

It will be appreciated, that when the damp-proof course is secured to the stile of the window frame, the remainder of the damp-proof course will extend inwardly from the stile 78, in continuation of that part of the damp-proof course which has been secured to the stile. The window frame is then placed in position, and the end of the wall is built up in the conventional manner, butthe part of the damp-proof course 40 which was extending inwardly from the stile is bent through 90 , and laid against the inside face 82 of the outer leaf 70. The cavity closing bricks 76 hold the damp-proof course in this bent condition, and mortar squeezed out from between the courses of the bricks in the outer leaf 70 and in the closure bricks 76, will tend to enter the slightly splayed formations provided by the flanges 52,64 and 54, 66.This assists in keying the mortar to the damp-proof course.

It will be appreciated therefore, that the dampproof course 40 provides the usual vertical dampproof course required between the outer leaf 70 and the closure bricks 76, and since the membrane 42 extends completely across the width of the closure bricks 76, this damp-proof course should prove very effective. Furthermore, the rib 45 rests against the inside face 82 of the outer leaf 70, and any moisture attempting to cross the cavity 74 from the face 82 of the outer leaf, would have to creep around the rib 45.

This is a further barrier to the travel of moisture across the cavity. In addition, the flange 68 is engaged against the inside face 90 of the closure bricks 76, and this provides yet another location for the damp-proof course.

Besides providing the usual vertical damp-proof course, the arrangement also provides a damp-proof course between the stile 78 and the outer leaf 70 of the wall, which as has been previously mentioned is highly desirable. The rib 44 bridges the outer edge of the joint between the outer leaf 70 and the stile 78, and prevents water entering that joint. If any mois ture does pass the rib 44, it can then only travel inwardly, by capillary action. If moisture manages to travel between the damp-proof course membrane 42 and the stile 78, it will have to pass the region where the damp-proof course is nailed to the stile, which represents a severe barrier, and it will than have to pass the region where the flange 58 is pressed against the stile 78. Following that, the moisture will have to traverse the usual groove 92 formed in the stile 78.Any moisture which manages to evade the rib 44 on the wall side of the membrane 42, can do no harm, because it is prevented from reaching the stile 78, or the plaster 88, or the closure bricks 76, by the damp-proof course itself.

It is also to be noted, that the flanges 48, 50 and 62 provide reinforcing to the damp-proof course, at the position where the latter is bent through 90 in order to provide the three moisture barriers previously described.

As a result of the construction which is shown in Figure 7, the following advantages have been achieved over the traditional construction methods: (a) The elimination of expensive and inconvenient mastic pointing at the joint between the stile and the end of the outer leaf.

(b) The prevention of cavity bridging by mortar crossing the inner longitudinal edge of the vertical damp-proof course.

(c) The provision of protection for the window frame itself from moisture contained in the outer leaf of the wall.

(d) The provision of three moisture barriers, namely (i) that between the outer leaf and the stile, (ii) that between the inner and outer leaves, and (iii) that between the outer leaf and the plaster in a single damp-proof course.

In Figure 8, there is illustrated a construction which includes a wall having an outer leaf 100 and an inner leaf 102, with a cavity 104 between them.

The end of the cavity is closed by three-quarter and quarter bricks 106 as previously described. In this case however, the end of the wall occurs at the opening for a door, and the stile of a standard timber door frame is illustrated at 108. The damp-proof course 40 is fitted in a very similar manner to that described with reference to Figure 7, but because the stile 108 is thicker than the stile 78, a wider part of the membrane 42 of the damp-proof course has to be used between the stile 108 and the end of the outer leaf 100. In this construction, the flange 62 is bent at right angles and secured to the inside face of the stile 108, and the flange 68 is bent at right angles to engage with the inner face of the closure bricks 106.In all other ways, the construction resembles that illustrated in Figure 7, and the damp-proof course functions in exactly the same manner as that described with reference to Figure 7.

In some instances, the architect may wish to employ a conventional bitumen impregnated felt damp-proof course to provide the vertical moisture barrier between the outer and inner leaves of the wall, and to cater for this possibility, a damp-proof course of somewhat different construction is illustrated in Figure 9. This damp-proof course 110 is formed as an extrusion in plastics material, in a similar fashion to that in which the previously described damp-proof course 40 is produced. In this construction, there is a membrane 112, formed with a tubular rib 114 along one longitudinal edge, but the membrane 112 has an overall width of only some 82 millimetres. There are six flanges 116, 118, 120, 122, 124 and 126 arranged in three pairs as illustrated, and it will be noted that the flanges 124 and 126 have their roots coinciding with the longitudinal edge of the membrane 112 which is opposite to the rib 114.

Referring now to Figure 10, there is illustrated a wall comprising an outer leaf 130 and an inner leaf 132 with a cavity 134 between them, there being the usual closure bricks 136. The stile 138 of a standard window frame is illustrated, in the conventional position, i.e. the position illustrated in Figure 1 of the drawings. Furthermore, a conventional bitumen impregnated felt damp-proof course 140 is fitted between the inside face of the outer leaf 130, and the end face of the closure bricks 136. All this therefore represents the traditional method of closing the cavity at the end where there is a window opening.

However, during the construction of the building, a length of the damp-proof course 110 equal to the total height of the window frame is cut off, and secured to the end of the stile 138 as illustrated in Figure 10. The rib 114 is engaged with the outer surface of the stile 138, and thereby provides a location for the damp-proof course, and nails 116 are used to secure the damp-proof course to the stile.

The flange 122 is bent at right angles, and nailed to the inside face of the stile 138, and the flange 120 is also bent at right angles and fitted into the joint between the outer leaf 130 and the closure bricks 136. The portion of the damp-proof course on the inside of the flanges 120 and 122 simply extends inwardly of the window frame, and becomes embedded in the plaster 142, when that is applied to the inside of the window reveal.

It will be appreciated that the damp-proof course 110 illustrated in Figures 9 and 10, is not so versatile as that illustrated in Figure 4, but it does provide an effective damp barrier between the outer leaf 130 and the window frame, and a further damp barrier between the outer leaf and the plaster 142. Furthermore, the rib 144 eliminates the necessity for mastic pointing. Turning now to Figure 11, there is illustrated a structure comprising an outer leaf 150 and an inner leaf 152 with a cavity 154 between them. The end of the cavity adjacent to a door opening is closed by the usual three-quarter and quarter closure bricks 156, and in this construction, a bitumen impregnated felt damp-proof course 158 provides the vertical moisture barrier between the outer leaf 150 and the closure bricks 156. Up to this point therefore, the construction is entirely conventional.The stile 158 of a standard timber door frame is shown in position against the end of the outer leaf 150, and it will be observed that the inner face of the stile 158 is in the same plane as the inside face of the outer leaf 150. The damp-proof course 110 is fitted to the stile 158, in similar fashion to the fitting of that damp-proof course to the window frame stile 138 described with reference to Figure 10. Ho ever, because the stile of the door frame is wider than that of the window frame, the outer flange 126 has to be bent at right angles and engaged against the inside face of the stile 158, and the corresponding flange 124 has to be bent at right angles and fitted into the joint between the outer leaf 150 and the closure bricks 156.Otherwise, the damp-proof course 110 is fitted to the stile 158 in the same manner as has been described with reference to Figure 10, and it functions in exactly the same manner as that described with reference to Figure 10.

Both the damp-proof courses illustrated in Figures 4 and 9, are provided with ribs which are of hollow cylindrical cross-section. However, referring to Figure 5, it will be seen that an alternative rib cross-section 160 could be employed along one or both of the longitudinal edges of the membrane.

This rib 160 is of hollow cross-section, but it has two flat sides at right angles to each other, one being a continuation of the membrane 42, joined by a curved section, so that it forms a quarter circle rib. It will be appreciated, that when the membrane 42 is pressed against the end 80 of the outer leaf of a wall, then the rib 160 can provide a particularly neat cover for the joint between the outer leaf and the stile of the window frame.

Figure 6 illustrates another possible construction, in which again there is a rib 170 of circular crosssection, but this is joined to the main portion of the membrane 42 between the flanges 46 and 58 on the one hand and the flanges 56 and 68 on the other hand, by a tapered section 172, which provides a smooth transition from the relatively thick rib section, to the thin membrane section.

Figure 12 illustrates some of the problems which can arise in cavity wall construction, when attempting to provide a horizontal damp-proof course. One brick of an outer leaf is shown at 180, and this is superimposed by a brick 182 of the next succeeding course. It is required to provide a damp-proof course between the bricks 180 and 182, but it is also necessary for aesthetic reasons, to have a mortar joint 184 between the two courses of bricks. A strip of conventional damp-proof course 186 is used, and this may be made of bitumen impregnated felt, or plastics material. The damp-proof course strip 186 is precut to the same width as the bricks 180 and 182 before the strip arrives at the building site, and therefore the bricklayer has no choice over the width of this strip.Ideally, the longitudinal edges of the damp-proof course 186 should be vertically aligned with the outer and inner faces of the brickwork, so that the damp-proof course provides a damp barrier extending across the full width of the outer leaf of the wall. However, the damp-proof course 186 is frequently fitted as illustrated in Figure 12, that is to say offset somewhat inwardly, so that its inside longitudinal edge projects very slightly into the cavity. This means that the outer longitudinal edge is set back from the outer face of the wall, and in addition to the mortar 188 which lies below the damp-proof course 186 and the motor 190 which lies above that damp-proof course, the bricklayer applies pointing mortar at the position 192 so that the outer longitudinal edge of the horizontal damp-proof course is concealed.

Now clearly, this pointing of the join between the courses 180 and 182 provides a better appearance, particularly since the longitudinal edges of the damp-proof course are sometimes damaged during transport, storage, or on the building site itself, and hence present at somewhat unsightly appearance, if they are visible on the outside of the wall. However, this pointing at 192 largely defeats the object of providing the damp-proof course in the first place, since it creates a moisture path from the brick 180, around the outer longitudinal edge of the damp proof course, into the mortar 190, and the brick 182 above the damp-proof course. In addition, because the damp-proof course is entirely concealed from the outside of the building, it is impossible to verify that the damp-proof course has been fitted at all places where it is required.

The inner leaf of the wall as shown in Figure 12 has a brick 194, superimposed by a brick 196 of the next succeeding course. Again, it is required to provide a horizontal damp-proof course, and for this purpose a strip of damp-proof course 198 is used, this being identical to the strip 186 used in the outer leaf of the wall. In the case of the inner leaf, there is no question of pointing over the edge of the damp-proof course, because the sheet damp-proof membrane positioned below the internal floor slab is tucked into the same horizontal brickwork joint as the horizontal damp-proof course in the wall. Any cladding such as plaster on the inside leaf is therefore above the horizontal damp-proof course.However, it is often difficult to align the damp-proof course precisely with the bricks of the inner leaf, and if the dampproof course is offset inwardly, as illustrated in Figure 12, then it is possible for mortar forming the joint between the courses 194 and 196 to accidentally form a bridge around the outside longitudinal edge of the damp-proof course as indicated at 200. It will be appreciated, that if a relatively long length of the damp-proof course is being laid, then once some bricks have been laid on top of it, it is virtually impossible to adjust the direction of the damp-proof course, and this may vary slightly from the direction of the wall itself, thus creating the possibility of some offsetting of the damp-proof course relatively to the wall as indicated in Figure 12.

In Figure 13, there is illustrated a special horizontal damp-proof course 202 which is extruded in plastics material, in similar fashion to the damp-proof courses which have been described with reference to Figures 4 and 9 of the drawings. This damp-proof course 202 has a membrane 204, ribs 206 and 208 of hollow circular cross-section extending along its longitudinal edges, and flanges 210,212,214 and 216. The overall width of the damp-proof course 202 is approximately the same as that of a brick. In Figure 13, a brick forming part of an outer leaf of a wall is shown at 218 and a superimposed brick 220 forms part of the next succeeding course of the wall.

It is required to provide a horizontal damp-proof course between the bricks 218 and 220, and this is achieved by laying the damp-proof course 202 in the mortar 222 between the two courses of bricks. If the damp-proof course is correctly fitted, then its ribs 206 and 208 will just close the ends of the mortar joint, and the outer rib 206 will prevent mortar pointing over the damp-proof course.

The practical difficulty with the construction illustrated in Figure 13, is that bricklayers rarely lay a layer of mortar under the damp-proof course. The result is illustrated in Figure 14, where it will be seen that the membrane 204 is lying almost flat on the brick 218, but the ribs 206 and 208 would not then be centralised over the mortar joint.Another difficulty with the damp-proof course illustrated in Figures 13 and 14, is that where it is necessary to joint two pieces of damp-proof course end-to-end, it would be necessary to produce butt joints between the ends of the ribs (since it would be impracticable to provide a lap joint comprising one rib on top of another), and butt joints are not permissible in damp-proof courses In Figure 15 there is illustrated a slightly modified damp-proof course 224 the membrane 226 of which has a width equal to the width of a brick, so that when in position as illustrated, the ribs 228 and 230 of the damp-proof course lie outside the respective faces of the leaf of the wall. It is then possible where a joint has to be made between two pieces of damp-proof course, to cut off part of the ribs on one of the pieces of damp-proof course in order to provide butt joints.Since these butt joints will be on the outside of the wall itself, they are acceptable. It will be appreciated however, that this construction does not overcome the problem of the bricklayer laying the damp-proof course directly on to the lower brick.

A better solution is therefore provided by the damp-proof course 240 which is illustrated in Figure 16. This again is produced by a similar method to that described with reference to Figures 4 and 9 of the drawings, and essentially comprises a membrane 242 having hollow circular cross-section ribs 244 and 246 along its respective longitudinal edges, but in this construction, the membrane 242 is slightly wider than a brick, and is joined tangentially to the ribs 244 and 246, so that each rib projects from only one face of the membrane 242.In fact, the distance between the insides of the ribs 244 and 246 is made equal to the width of a brick, and hence, the damp-proof course 240 can be simply pressed down on to the top of the brick course 218, the ribs 244 and 246 engaging respectively with the inside and outside faces of the brickwork in this course and thus locating the damp-proof course 240 precisely with respect to the course of bricks beneath it. This provision for precise location of the damp-proof course is extremely important, since in itself it helps to avoid some of the problems which have been discussed with reference to Figure 12 of the drawings.

It is then possible for the bricklayer to apply mortar 248 on top of the membrane 242, before laying the next course of bricks 220, and if desired, the mortar joint can be pointed on the outside. There is no possibility of any such mortar pointing bridging around the outside edge of the damp-proof course, because the membrane 242 extends across the full width of the joint between the two courses of bricks, and because the rib 244 presents a barrier, to which the mortar could not effectively adhere. Furthermore, the rib 244 will appear on the outside of the wall, giving an indication to anyone inspecting the building, that the damp-proof course has been correctly fitted, and since this rib is relatively small in .cross-section and will lie tightly against the outer surface of the wall, it will present quite a neat detail of the building which need not be concealed.

Incidentally, the ribs 244 and 246 on the horizontal damp-proof course need not be so large as those provided on the vertical damp-proof courses previously described. It will be appreciated that the ribs provided on the horizontal damp-proof course could have the cross-section illustrated at 160 in Figure 5, although it is thought desirable to use the circular cross-section rib.

Finally, Figure 17 illustrates an external leaf 250 and an internal leaf 252 of a cavity wall, with a cavity 254 between them. The detail which is illustrated occurs over the top of a window opening, and a concrete lintel 256 is fitted in the internal leaf of the wall. The lintel has a tapering cross-section as illustrated, so that at its lower end, it almost touches the inside face of the outer leaf 250, whereas at its upper end, it is aligned with the brickwork of the inner leaf 252. Plaster 258 is applied under the lintel 256, to clad the top of the window reveal.

The head 260 of a standard timber window frame is illustrated, in the position corresponding to that of the stile shown in Figure 7, that is to say, with the inside face of the head in alignment with the inside face of the outer leaf 250 of the wall. A conventinal angle iron 262 is secured to the brickwork of the outer leaf 250, so that one flange of the angle iron extends into the cavity, and the other extends over the head 260.In addition, a special damp-proof course 40, excepting that it is considerably wider, the distance between the roots of the flanges 50 and 62 on the one hand and 52 and 64 on the other hand, being such that it is possible to bend the damp-proof course into the configuration shown in Figure 17, where it provides a so-called cavity tray, part of the damp-proof course providing a moisture barrier between the outer leaf 250 and the window frame 260, the flange 60 providing a moisture barrier between the head 260 and the plaster 258, and the remainder of the damp-proof course providing a moisture barrier between the cavity and the inside of the lintel 256. It will be noted that the rib and the inner end of the damp-proof course is trapped in the joint between the top side of the lintel 256 and the next succeeding course of bricks 252, in order to ensure that the damp-proof course is held taut.

Claims (21)

1. A structural assembly comprising first and second structural elements (as herein defined) arranged close to each other, and a damp-proof course having a membrane with a rib along one longitudinal edge, the membrane being located between the two structural elements, and the dampproof course extending across the full width of at least one of the two elements.

2. A structural assembly as claimed in Claim 1, in which the rib locates along an edge of a first of the structural elements.

3. A structural assembly as claimed in Claim 2, wherein there is a second rib along the other longitudinal edge of the membrane, this second rib locating along an opposite edge of the first of the structural elements.

4. A structural assembly as claimed in any one of Claims 1 to 3, in which the or each rib is of hollow cross-section.

5. A structural assembly as claimed in Claim 4, in which the rib is in the form of a tube of substantially circular cross-section.

6. A structural assembly as claimed in Claim 5, in which the membrane extends tangentially to the circular cross-section of the rib so that the rib projects only from one face of the membrane.

7. A structural assembly as claimed in any one of Claims 1 to 6, in which at least one flange projects from the membrane at a position intermediate its ends, and is engaged with a face of one of the structural elements at right angles to the face of that element which faces the other element.

8. A structural assembly as claimed in any one of Claims 1 to 7, in which the membrane is bent through a right angle so that a first part of its lies contiguous with one face of the first of the structural elements and the other part lies contiguous with an adjacent face of that element at right angles to the first face.

9. A structural assembly as claimed in Claim 8, in which there is a third structural element, arranged in close juxtaposition to the first element, facing the said adjacent face of the first element, so that the said other part of the membrane is located between the first element and the third element, this other part of the membrane extending across the full width of one of the facing surfaces of the first and third elements.

10. A structural assembly comprising a cavity wall having inner and outer leaves, a stile, head or sill of a doororwindowframe arranged closely adjacent to an end of the cavity wall, and a damp-proof course having a membrane located between the end of one of the leaves of the wall and the stile, head or sill, the damp-proof course having a rib extending along one edge of the membrane and engaging in a corner formed between the said one leaf of the cavity wall and the stile, head or sill, and the damp-proof course having a part bent through a right angle from the membrane at the opposite side of the stile, head or sill to the rib, so as to locate against either a face of the stile, head or sill or against a face of the said one leaf which is in the cavity.

11. A structural assembly as claimed in Claim 10, in which there is a second part of the damp-proof course bent at right angles from the membrane in the opposite direction to the first bent part, so that one bent part locates on a face of the stileheador sill, and the other locates against a face of the said one leaf which is in the cavity.

12. A structural assembly comprising a cavity wall having inner and outer leaves, a stile, head or sill of a window or door frame arranged closely adjacent to an end of the cavity wall, there being closure means closing the end of the cavity and a damp-proof course which cmprises a membrane having a rib along one longitudinal edge, a first part of the membrane being located between the end of the cavity wall and the stile, head or sill and extending completely across the joint between the stile, head or sill and the cavity wall and a second part of the membrane bent at right angles to the first part and being located between the closure means and one of the leaves of the cavity wall, this second part of the membrane extending completely across the joint between the closure means and the leaf, the damp-proof course also having a rib extending along a longitudinal edge of the membrane and located in the corner between the stile, head or sill and the end of the cavity wall.

13. A structural assembly as claimed in Claim 12, in which a second rib is formed along the other longitudinal edge of the membrane and rests against the face of the leaf of the wall which faces the closure means on the inside of the closure means.

14. A structural assembly as claimed in Claim 12 or Claim 13, in which a flange projects from the membrane and engages with the inner end face of the closure means.

15. A structural assembly as claimed in any one of Claims 10 to 14, in which the rib which engages in the corner between the stile, head or sill and the end of the cavity wall, bridges any space between the stile, head or sill and the end of the cavity wall, to form a water seal therebetween.

16. A structural assembly as claimed in any one of Claims 10 to 15, in which there are one or more intermediate flanges projecting from the membrane of the damp-proof course intermediate its rib and the right angle bend, which flange or flanges engage(s) in mortar squeezed out from the leaf of the cavity wall against which it is locted.

17. A structural assembly as claimed in any one of Claims 11,12,13,14, (so far as it depends from one of Claims 11 to 14) and 16, in which there are one or more intermediate flanges projecting from the membrane of the damp-proof course intermediate the right angle bend and the end of the membrane which is located in the cavity.

18. A structural assembly as claimed in any one of Claims 1 to 6, in which the two structural elements are parts of a vertical wall one above the other, the damp-proof course providing a barrier to rising damp.

19. A structural assembly as claimed in any one of Claims 1 to 18, in which the damp-proof course is made in plastics material.

20. A structural assembly as claimed in any one of Claims 1 to 19, in which the damp-proof course membrane is flexible.

21. A structural assembly constructed and arranged substantially as herein described with reference to Figure 7, Figure 8, or Figure 10, or Figure 11, or Figure 13, or Figure 14, or Figure 15, or Figure 16, or Figure 17, or any of those figures as modified by either of Figures 5 and 6, of the accompanying drawings.