DRAINAGE AND VENTILATION SYSTEM FOR BUILDING WALL ASSEMBLIES

Abstract: A continuous fluid conducting medium (20) establishes and maintains an air space (14) and occupies substantially all of the air space (14) between the exterior wythe (12) and the interior wythe (15) of a building wall to provide a drainage and ventilation conduit for removing moisture that enters the wall system. The fluid conducting medium (20) may be made of non-woven polymer textiles. Different grades of the non-woven textile can be installed in a masonry cavity wall (10) air space (14), serve as a non-woven polymer mesh (27) for installation in the weeps at the lowermost level of the wall so that the weeps (28) will not become obstructed, as vent mesh (29) at the uppermost level of the wall. Another grade forms a non-woven mat (68) for installation between the structural wall assembly (98) and the stucco (62) or EIFS (64) in a veneer wall assembly (60).

Description: DRAINAGE AND VENTILATION SYSTEM FOR BUILDING WALL ASSEMBLIES TECHNICAL FIELD The embodiment relates to several common types of building wall assembly systems used in commercial and residential buildings Specifically, the embodiment may be used in masonry cavity walls, cement plaster finish systems (stucco) and Exterior Insulation Finish Systems (EIFS) Stucco and EIFS are referred to in this disclosure as typical "veneer" wall assemblies A cavity wall generally has a structurally significant inner 'wythe" made of concrete block or other framing materials, and an exterior wythe, which is typically non-load bearing, made of brick, stone, or other masonry material Between the wythes is a cavity which provides an air space which must be kept open for the lifetime of the building to allow any accumulation of water to drain and air to circulate The embodiment prevents mortar and debris from entering the cavity, bridging the ties, obstructing the air space and blocking the drainage weeps In addition, a new ventilation system for head joint vents and wall cap vents is described Pressure equalization within the cavity is assured by application of this embodiment The likelihood of premature failure of the cavity wall is greatly reduced by using the construction system disclosed herein which prevents the air space and weeps from becoming obstructed during or after building construction Stucco walls generally have a structurally significant masonry wall or a sheathed framing system that supports metal lath embedded in wet stucco Stucco is cement plaster applied to the outside of a wall, usually in several layers, to create a weather-resistant finished surface or exterior layer The sheathing is typically covered with a protective air infiltration barrier such as building felt or other material that resists water penetration but allows water vapor to escape Metal lath is mechanically fastened over the air infiltration barrier to secure the stucco to the structure Cracks may develop in the stucco finish due to shrinkage of the cementitious materials, movement of the building or other causes Such cracks create a potential for water infiltration through the stucco barrier to the structural components of the building Water accumulation may cause rotting of wooden materials, corrosion of metallic components, degradation of interior finishes, and damage to electrical devices located in a wall Traditionally, stucco has been installed in direct contact with the air infiltration barrier and sheathing without including specific methods for drainage and ventilation to remove accumulated moisture The embodiment provides drainage to remove water that penetrates the stucco finish and ventilation to dry the wall assembly The embodiment removes water by allowing any water that penetrates the stucco to flow through a non-woven mat layer interposed between the air infiltration barrier and the stucco Gravity moves the water through the non-woven mat to weep holes installed at the bottom of the finished wall The weep holes allow air to circulate through the non-woven mat and vent water vapor to the atmosphere An additional benefit of the present embodiment is that the resilience of the non-woven mat allows more thorough penetration and encapsulation of the metal lath by the cementitious coating An EIFS wall system has an exterior layer made of an acrylic-modified, Portland cement containing material that is customarily applied directly to expanded polystyrene board insulation or to a cementitious structural sheathing material EIFS is applied to the outside of a wall in a thin exterior layer, approximately Vβ," whereas the thickness of traditional stucco is %" to % " EIFS manufacturers may specify that the finished exterior layer is actually made from multiple layers of coating materials EIFS typically includes a separate reinforcing product such as glass fiber fabric The appearance of an EIFS wall is similar to traditional stucco systems As originally introduced, EIFS was considered a barrier system because it was believed that it would reliably prevent water penetration Experience has shown that EIFS, like stucco, can develop cracks that allow water to penetrate and damage the building components in all of the same ways that water damages stucco walls The EIFS industry has responded to the problem of water damage to the system by introducing the concept of water management This concept recognizes that a wall can seldom be constructed in a way that guarantees water will never penetrate the completed assembly However, the materials and methods used in attempts to adequately manage water penetration present undesirable limitations The embodiment provides drainage to remove water that penetrates the EIFS and ventilation that dries the wall assembly The embodiment removes water by allowing any water that penetrates the EIFS to flow through a fibrous mesh, or non-woven mat, interposed between the EIFS substrates and the polymer based coating Water moves through the non-woven mat to weep holes installed at the lowermost level of the finished wall Air circulates through the non-woven mat and vents water vapor to the atmosphere BACKGROUND AND SUMMARY In cavity wall construction, an inner wall portion or wythe is usually made of concrete block, wood framing, or steel framing When frame construction is used, sheathing materials such as wood, gypsum board or cementitious sheet material, are installed on the outer side of the framing members Board insulation is often applied to the outer side of the concrete block or sheathing and ordinary interior finish materials to the interior side of the inner wythe. A second, exterior wythe is constructed using the desired exterior finishing material such as brick, block, or stone to cover the insulation or sheathing. The facing sides of the two wythes are typically separated two to four inches to form a cavity; the cavity provides an air space and may include insulation. Walls formed from two wythes separated by an air space of less than two inches are sometimes denominated "void collar joint walls." For simplicity, this disclosure will refer to both types as a "cavity wall." Regardless of the material used in construction of the wythes, it is essential that an air space be maintained between them. It is also essential to provide a way to remove moisture from the cavity. Drainage holes, openings, or channels called "weeps" are normally provided at the first course of brick above grade elevation, at lintels and at other flashings which direct water away from the interior of the building. Moisture can enter the cavity due to condensation, permeation, plumbing faults, roof faults, and cracks in the masonry which inevitably occur over time, among other ways. It is impossible to prevent small amounts of water from penetrating brick or other masonry walls because the materials are porous and prone to cracking. If water accumulates in the cavity between the inner and outer masonry portions of a wall, problems with degradation of the brick, efflorescence, interior damage, and damage to foundations can develop. A common problem in cavity wall construction is that excess mortar and other debris may fall into the cavity and create places where moisture can accumulate. If mortar or other construction debris obstructs the weeps or provides a place where water can pond, the build-up of moisture can damage insulation, carpets, interior wall finishes and furnishings. Efflorescence is another problem resulting from accumulation of water in the wall. In addition, the freezing of accumulated moisture can cause spalling and other damage. Although various techniques have been implemented in attempts to prevent air spaces, vents and weeps from becoming blocked, but none has proven adequate. One technique to keep the cavity wall air space open is to increase its size. However, that necessarily results in increased foundation size, thicker walls, more expensive window and door installations, and greater labor costs. Other common techniques also have serious drawbacks. For example, the cavity is sometimes filled with pea gravel to prevent dropped mortar from filling the weeps. Pea gravel itself will sometimes block the weeps or else simply raise the elevation at which mortar accumulates to the height of the pea gravel. The installation of pea gravel is laborious, especially as the wall increases in height. Another technique requires construction workers to lift a board through the cavity to dislodge and remove dropped mortar. In the course of lifting a board through the cavity, the board may catch on bricks which have partially set and compromise the integrity of the bond of the mortar to the brick. The technique is also disruptive of the normal work of the mason and is difficult to accomplish when horizontal joint reinforcement materials are incorporated into the wall design. Another technique is described by Ballantyne in U.S. Patent No. 4,852,320 and requires the mason to install inclined shapes of sheet or extruded metal within the air space of the cavity wall. In U.S. Patent No. 5,230,189, Sourlis describes shapes made of polymer mesh for catching mortar debris as it drops into the wall cavity. Although such techniques may be improvements to traditional methods, they do not overcome all of the problems associated with cavity wall construction. First, the on-site installation is difficult to properly supervise because the components are hidden from view almost immediately after installation. In the event that problems with the installation are discovered, correction is likely to be expensive, perhaps prohibitively so. Second, the techniques and equipment are designed to trap and collect debris. Once collected, that debris may itself accumulate water that could lead to structural damage. Another shortcoming of previous attempts to solve the problem is the expense of implementing them. Most are relatively unproven and represent a substantial initial expense to obtain an uncertain benefit. What is needed, then, is a way to keep excess mortar and other construction debris out of the air space from the very beginning. The present embodiment meets that need by preventing, from the outset, creation of excess mortar debris which could block the weeps and allow moisture to accumulate, and by excluding other debris from the cavity by preventing it from entering in the first place. Not only does the present embodiment prevent blockage of weeps, it also prevents bridging of masonry ties with mortar. It is expected to reduce construction costs by allowing smaller cavity dimensions which can reduce the cost of foundations and window and door openings. It is especially significant that the present embodiment is expected to reduce the cost for mortar by reducing waste while increasing productivity. The present embodiment also allows the specification of smaller air spaces thereby providing space for additional wall insulation and/or smaller foundation sizes. The cavity-filling mesh may be formed from any non-absorbent, non-woven co-polymer fibers. It is believed preferable that the cavity-filling mesh be formed of non-woven polyester polymer fiber with 80% to 100% of the fibers being 200 denier and 0% to 20% of the fibers being other sizes. It has been found that a satisfactory mesh can include up to about 20% fibers in the range of 15 to 45 denier. The binder used to hold the polyester fiber mesh in place preferably comprises 25% to 65% of the final product by weight. It is believed preferable to use a flame-retardant PVC, EVCL polymer type binder when using polyester fibers and to have the weight of the binder comprise approximately 50% of the product, by weight. No limitations to the acceptable ratio of binder to fiber have been established experimentally. Satisfactory results have been obtained using ratios of binder to fiber in the range from 30% to 70%. The weight of the mesh, in a %" thickness, is between five and ten ounces per square yard, and preferably approximately eight ounces per square yard. The choice of particular polymers for the fibers and binders is not critical to the embodiment and may vary depending on the price and availability of alternatives. For the purposes of fabricating this embodiment, all polymer materials that can be readily formed into a suitable non-woven mesh are deemed equivalent. Acceptable mesh samples have also been made using nylon, polyethylene and polypropylene. High quality samples of the mesh have been produced using the air-laid process from recycled polyester staple, the material currently believed preferable. It is likely that other recycled materials, perhaps mixed, could be used as well. Mesh used to form head joint weeps and cap vents could be made in the same manner as the mesh used in the cavity. However, it is believed preferable to use thinner fibers than those comprising the fluid-conducting medium. Compared to cavity non-woven mat, weep and vent mesh is preferably fabricated using a higher density of thinner fibers, resulting in less void space and a lower ratio of binder to fiber. It is anticipated that an ultraviolet-resistant binder would be required in the head joint weep and cap vent mesh to prevent photochemical degradation. With or without insulation, the fluid-conducting medium is attached to the first wythe (the inner wythe) and disposed within the air space at a distance of approximately %" from the inner surface of the second wythe (the exterior wythe). The mortar expressed from the inner side of the bricks as they are laid will be prevented from falling because it would become entangled in the mesh fibers. The expressed mortar would not extend across all of the distance from between the second wythe and the first wythe whether it is fitted with board insulation or other sheathing material. Thus, an uninterrupted air space will be maintained from the top to the bottom of the wall cavity and throughout the entire length of the wall to assure proper moisture drainage and air circulation. Included in the present embodiment is the optional provision of ventilation mesh for use in vented masonry cavity wall systems. Mesh panels cut to the size of the end section of the masonry unit being used to construct the exterior wythe may be installed in place of mortar in some of the "head" (vertical) joints near the bottom of a wall. The mesh, when made with ultraviolet resistant binder and fiber, is believed to be superior to previously known drainage devices. The non-woven polymer mesh will exclude insects and other vermin from the air space more effectively than the currently known drainage inserts. In addition, the non-woven polymer mesh may be fabricated in colors and textures that resemble the appearance of mortar. It is possible for designers to specify adequate drainage and ventilation without compromising the aesthetic appeal of the exterior facade. The mesh, or heavier formulations of the mesh, can not only be used between the brick head joints, but may also be used at the top of the wall beneath the capstone or wood blocking and flashing to provide an opening for air ventilation and circulation. Ventilating the cavity between the wythes can reduce the formation of frost and mildew by allowing any moisture that enters the cavity, whether as liquid or vapor, to escape rather than accumulate Another advantage of the presently disclosed system is that it provides improved insulation performance. Mortar bridging an air space allows thermal transfer between the wythes across the air space. The embodiment prevents this thermal transfer by preventing mortar from entering the air space. In addition, when mortar bridging is present, water may accumulate and degrade the insulation. The non-woven mat is expected to provide enhanced thermal properties compared to an air space alone. A further advantage of the present embodiment is that mortar is prevented from accumulating on the adjustable masonry ties which are designed to accommodate normal movement of the wythes. Differential movement caused by thermal expansion and contraction of the building materials can result in cracking if mortar obstructs the air space or bridges the masonry ties. This embodiment allows adjustable ties to function as intended rather than as limited by the accumulation of mortar. In addition, the structure may be less susceptible to damage due to seismic activity. It is to be understood that, although the fluid-conducting medium is preferably bonded to insulation sheet material in the facility where the product is manufactured, it may also be pressed into place at the construction site or affixed using any suitable adhesive. It is anticipated that sheets of fibrous mesh fluid-conducting medium could be installed by placing them between the masonry ties. It is further to be understood that the preferred resilience and strength of the material will be sufficient to allow it to hold mortar but also soft enough to permit workers to readily install masonry ties and to otherwise work with it easily. A further advantage of the embodiment disclosed herein is that it provides a method for equalizing air pressure throughout the cavity wall when used in conjunction with open, or vented, head joints in lieu of rope wicks. When wind is blowing, the pressure on the down-wind side of the building is less than the pressure on the up-wind side. If the outside of the building is wet, for example due to rain, the existence of any significant pressure differential will cause water to be drawn from the outside of the building through even very small cracks, defects, and other openings in the masonry In addition to climatic causes, a pressure differential exists between the interior and the exterior of most buildings due to the operation of mechanical air handling systems that exhaust "old" air and introduce fresh air resulting in a net negative interior pressure The presence of obstructions in the air space or weeps can result in wet spots during rains which can be very difficult to correct The present embodiment, by preventing any obstruction of the cavity air space vents or the weeps, allows air pressure to equalize at all points on both sides of the outer wythe and thereby reduces the extent of water infiltration The embodiment is expected to improve the overall quality of the constructed building The expected improvements include reduced re-work, fewer complaints by owners, and longer building life In order to obtain generally satisfactory cavity wall construction, the industry standard recommendation is that masonry cavity walls be configured with an air space of from 1 " to 2" in addition to any insulation (normally 4" total, including insulation) The present embodiment provides the benefit sought by the industry using a wall cavity that is only 2" (nominal) The cost of the materials used in the embodiment are offset by savings resulting from reduced mortar waste, reduced foundation size, lower costs to construct window and door openings, reduced costs for steel members such as lintels, cap blocking and flashings, and improved productivity Unlike those approaches intended to collect construction debris which enters the cavity air space, the present embodiment may lower overall construction costs, that benefit is complemented by easier installation and improved quality of the final product The figures of the present disclosure that depict masonry cavity walls show a typical installation with brick exterior finish, a clearance space of %", a mesh thickness of Vz to %", an insulation layer of V/z to 2", and an interior structural masonry wall of concrete block The system of the present disclosure provides the benefits normally associated with a wall having a nominal 4" cavity in a wall having a nominal 2" cavity It is well understood that construction costs for a wall with a 2" cavity are much lower than the costs for a wall having a nominal 4" cavity It is believed that the mat thicknesses most commonly used will be in the range of %" to 2" Some applications may require other mat thicknesses Alternatives to masonry finished wall systems include veneer wall assemblies that are finished with cementitious materials such as stucco and EIFS Conventional stucco and EIFS walls, like masonry cavity walls, can be damaged by water penetration when the installation does not provide specific, effective provision for removing water and venting water vapor to the atmosphere In stucco construction, an inner structural wall assembly, or wythe, is usually made of concrete block, wood framing, or steel framing When frame construction is used, sheathing materials such as wood, gypsum board or cementitious sheet material are installed on the outer side of the framing members Board insulation may be secured to the outer side of the concrete block with steel framing A stucco exterior layer, analogous to the outer wythe of masonry cavity wall construction, is applied to metal lath that has been affixed to the structural wall assembly Stucco finishes are typically applied in several layers to achieve a thickness of approximately In EIFS construction, as with stucco construction, an inner structural wall assembly, or wythe, is usually made of concrete block, wood framing, or steel framing When frame construction is used, exterior sheathing materials such as wood, gypsum board or cementitious sheet material are installed on the outer side of the framing members Board insulation may be secured to the outer side of concrete block with special-purpose, often proprietary, fasteners Similarly, board insulation may be secured to wood framing or steel framing over the exterior sheathing materials An EIFS exterior layer, comprised of finish coating materials, is somewhat analogous to the outer wythe of masonry cavity wall construction However, the EIFS finish coating materials have typically been applied in a thickness of approximately Vβ" directly to the board insulation or exterior sheathing Wall system failures due to water penetration and accumulation have been caused by the absence of a cavity and air space in traditional EIFS assemblies Regardless of the material used to make the exterior layer, it is essential that an air space or cavity be maintained between the exterior layer and the structural wall assembly It is also essential to provide a way to remove moisture from the air space or cavity Drainage weeps must be provided at the lowermost level of the exterior layer, at lintels and at other flashings to direct water away from the interior of the building Moisture can penetrate the exterior layer through shrinkage cracks, window and door openings, inadequate flashings, improperly applied or failed sealants and other gaps In addition, moisture can accumulate between the exterior finish coating and the structural wall assembly, among other ways, as the result of condensation, permeation, plumbing faults, roof faults, vapor barrier failures, and cracks that inevitably occur over time Wood rot, framing degradation, metal corrosion, sheathing disintegration, and interior finish deterioration are some of the problems that occur when water accumulates between the exterior finish coating and the structural wall assembly One important characteristic of the coatings used in constructing these veneer wall assemblies is that they have low permeability Although the coatings were intended to create an impenetrable barrier to moisture, that barrier could seldom be perfectly maintained Moisture that penetrated to the interior structural wall escaped slowly in the absence of a drainage and ventilation system For this reason, even small defects in the barrier coating of a veneer wall assembly led to significant moisture accumulation over time The damage caused by accumulated water has forced the manufacturers of the materials used in this type of construction to adopt the concept of water management for these finish systems Since traditional methods of veneer wall construction had no provision to remove this accumulated moisture it has recently become necessary to create components intended to drain water from these wall assemblies One limitation of a recently introduced veneer wall drainage product is that the drainage material can be installed only on the interior side of the thermal board insulation The effect of providing drainage at the interior side of the board insulation is that the ventilation provided by the drainage material introduces outdoor air to the temperature-controlled side of the thermal envelope In climates where year-round cooling may be required, warm moist air that enters through a drainage component will tend to condense This condensation will contribute to potential moisture damage In addition, when water vapor condenses, heat is released creating additional load on the cooling system In climates having greater heating requirements, the drainage material provides a channel for cold air to enter the thermal envelope There is a danger that this solution may replace one problem with another Veneer wall assemblies, even with the constraints identified above, remain desirable for several reasons Design opportunities are greater than those afforded by many other techniques Lightweight materials used in veneer wall assemblies reduce labor and transportation costs Material costs, especially for EIFS wall assemblies, are lower than those for comparable exterior systems The expansive selections of colors and textures that are available at reasonable cost augment aesthetic possibilities These and other benefits can be realized by overcoming the known limitations of veneer wall assemblies These potential benefits are widely known in the construction industry These benefits, unfortunately, cannot be realized in the absence of effective solutions to the acknowledged problems Persons skilled in this art have long recognized the need to overcome the disadvantages of the techniques and products presently available This disclosure presents, for the first time, an effective solution to the existing problems of veneer wall assemblies Not only is the present embodiment versatile, moderately priced, and easily installed, it also provides benefits not possible using traditional methods and materials The present embodiment comprises a non-woven mat fitted to the exterior side of board insulation and secured to the structural wall with mechanical fasteners The exterior layer is applied to the outside of the non-woven mat that makes up the fluid-conducting medium The non-woven mat may also be installed at the interior side of the board insulation Reinforcing fabric or metal lath may be installed on the outer side of the non-woven mat and board insulation combination and held in position with fastener plates and conventional mechanical fasteners A fastener plate specifically adapted for use with this non-woven mat is disclosed, although other fastener plates might adequately secure the non-woven mat in place It is also possible that EIFS coating materials could be applied directly to the non-woven mat Embodiments having the non-woven mat affixed to the board insulation prior to delivery to the construction site may prove to be efficient and convenient It is anticipated that the non- woven mat may be bonded to the board insulation with adhesive compounds or heat by a manufacturer It is also anticipated that some jobs will require field application of the non-woven mat A continuous, fluid-conducting channel is created by the non-woven mat An advantage of this non-woven mat is that it conducts the water that penetrates the exterior layer to weeps installed at the lowermost level of the wall Water may then drain from the structure through the weeps A further advantage of the present embodiment is that any residual water is dispersed through the non-woven mat This residual moisture can be removed as vapor by ventilation of the air space that is made possible by the fluid-conducting medium, or non-woven mat Ventilating air is admitted to the air space through stucco starter strips, EIFS starter strips, and alternate EIFS starter strips Each of the starter strips is designed to be inverted and used also as a termination strip at the uppermost level of the wall The weep holes that provide drainage of liquid from the air space also serve as vents Air can flow into the starter strip weep holes at the lowermost level of the wall, through the air space created by the non-woven mat, and then out the vents created by the weep holes of the inverted starter strip located at the uppermost level of the wall It is to be understood that the air space, because it is continuous, also provides wind and atmospheric pressure equalization It is anticipated that the non-woven mat will limit thermal transfer from the exterior layer to the structural wail assembly because the non-woven mat isolates the cementitious materials from direct contact with other wall materials Another advantage provided by the present embodiment is that the metal lath can be more completely embedded into the stucco cementitious material This improved integration of the reinforcing component within the exterior layer will strengthen the stucco The improved embedding of the metal lath is the result of the compressibility and porosity of the non-woven mat that allows the wet stucco to completely surround the reinforcing metal lath Similarly, the EIFS coating material and the reinforcing fabric integrate more completely When EIFS exterior layer is applied, trowel pressure forces the coating material all of the way through the openings in the reinforcing fabric assuring that the strands are throughly encapsulated It is believed preferable to fabricate the non-woven mat similar to the mesh used to form head-joint weeps and cap vents However, the non-woven mat may be formed of a higher density of thicker fibers resulting in less void space, but also a higher ratio of binder to fiber The reason for higher density and increased binder is to provide a higher and more uniform lateral load-bearing capacity with better support for the exterior layer Experienced design professionals understand that water will invariably reach the inner side of the weather-resistant layer of any building wall assembly system That understanding has prompted designers to search for methods and materials to manage that water A great deal of effort has been directed toward developing improved materials that will, somehow, make the exterior weather barrier impervious to water Unfortunately, no effective integrated water management system for wall assemblies has been developed prior to the drainage and ventilation system now disclosed The present embodiment satisfies this previously unmet need It teaches an integrated drainage and ventilation system that prevents water damage by providing a practicable water management system This solution may be applied to several popular wall systems In the most basic terms, this system works by providing a continuous conduit that drains water from between the layers of any multiple wythe wall assembly It also ventilates the conduit by creating and maintaining an effective air space This integrated system uses new methods and materials to create the continuous conduit Non-woven textiles have been adapted for installation at each type of building component These polymer meshes and mats were specifically designed to serve as masonry cavity mat, veneer system mat, and vent/weep meshes These integrated products accomplish water management through this interconnected drainage and ventilation system BRIEF DESCRIPTION OF THE DRAWING Fig 1 shows an exploded isometric view of a preferred embodiment Fig 2 shows a cross-sectional detail of the embodiment depicted in Fig 1 wherein the masonry cavity wall terminates at a lintel above a building opening Fig 3 shows a cross-sectional detail of an embodiment wherein the inner wythe is a stud structure system Fig 4 shows a cross-sectional detail of the embodiment depicted in Fig 1 wherein the unobstructed air space is more fully illustrated and the air pressure equalization properties of the embodiment are shown Fig 5 shows an isometric detail of the embodiment depicted in Fig 1 taken along line A-A Fig 6 shows an isometric detail of the embodiment depicted in Fig 1 taken along line A-A wherein the mesh material is not bonded to insulation or other sheet material Fig 7 shows a cross-sectional detail of the mesh holding mortar expressed from a mortar joint Fig 8 shows a cross-sectional detail of a masonry wall with a stucco finish Fig 9 shows a cross-sectional detail of a wood framed wall system with a stucco finish Fig 10 shows a cross-sectional detail of a metal framed wall system with a stucco finish Fig 11 shows a cross-sectional detail of a masonry wall with EIFS wherein the non-woven mat is located between the insulation and the polymer based exterior layer Fig 12 shows a cross-sectional detail of a masonry wall with EIFS wherein the non-woven mat is located between the masonry and the insulation Fig 13 shows a cross-sectional detail of a wood framed wall system with EIFS wherein the non-woven mat is located between the insulation and the polymer based finish coating Fig 14 shows a cross-sectional detail of a wood framed wall system with EIFS wherein the non-woven mat is located between the insulation and the cementitious sheathing material Fig 15 shows a cross-sectional detail of a metal framed wall system with EIFS wherein the non-woven mat is located between the insulation and the polymer based coating Fig 16 shows a cross-sectional detail of a metal framed wall system with EIFS wherein the non-woven mat is located between the insulation and the cementitious sheathing material Fig 17 shows an isometric detail of the non-woven mat termination drain and vent extrusion depicted in Fig 8 Fig 18 shows an isometric detail of the non-woven mat termination drain and vent extrusion depicted in Fig 13 and Fig 15 Fig 19 shows an isometric detail of the non-woven mat termination drain and vent extrusion depicted in Fig 14 Fig 20 shows a cross-sectional detail of a metal framed wall system with EIFS wherein the non-woven mat is located between the insulation and the polymer based coating Fig 21 shows an isometric view of the fastener plate depicted in Fig 1 1 , Fig 13 and Fig 20 Fig 22 shows an cut-away isometric view of the embodiment DETAILED DESCRIPTION OF THE DRAWING Fig 1 shows a masonry cavity wall 10 constructed on a foundation 11 which supports an exterior (or second) wythe 12 separated by an air space 14 from an interior (or first) wythe 15. The interior wythe 15 may be made of concrete block 16 as shown in Fig 2, wood or steel framing 17 as shown in Fig 3, or a variety of other materials including, but not limited to, structural clay tile, wood, hollow brick, and concrete The exterior wythe 12 is preferably made of brick 18 but may be made of other masonry materials including, without limitation, rock, artificial stone, concrete, block, stone, glass, and the like The cavity air space 14 is provided with board insulation 19 to which is attached a fluid-conducting medium 20. This fluid- conducting medium 20 is a material which allows gases, including air, and liquids, including water, to pass through it with negligible resistance but generally prevents solid materials from passing through it The fluid-conducting medium 20 is preferably made of fabric non-woven mat bonded to standard extruded or expanded polystyrene foam board insulation 19 as shown in Fig 5 The fluid-conducting medium 20 may also be fabricated, sold, and installed separately as illustrated in Fig 6 Although the illustrated fluid-conducting medium 20 is a coarse non- woven mat, it is to be understood that other equivalent materials and techniques may be used in its fabrication The fluid-conducting medium 20 may be attached to any materials used to construct the first wythe For example, when the side of the first wythe defining the cavity is made of gypsum board sheathing 22, the fluid-conducting medium 20 could be bonded to the gypsum board or to board insulation 19 as shown in Fig 3 The wythes are normally constructed to yield a cavity width of two to four inches in order to allow for air circulation and insulation 19 between the wythes, however, the exact dimension of the cavity may vary Both wythes of the wall 10 normally rest on a single foundation 11 which may be cantilevered or stepped to provide support for the exterior wythe 12. The foundation 11 is normally covered with a mortar cant 24 which slopes downward from the cavity side of the interior wythe 15 to the exterior A masonry flashing 26 communicating between the interior wythe 15 and the exterior of the wall 10 rests on a mortar cant 24 so that any moisture in the cavity will drain to the exterior of the wall 10 A non-woven polymer mesh 27 may be used to fill drainage openings called "weeps" 28 which communicate between the exterior of the masonry cavity wall 10 and the air space 14 Weeps 28 drain moisture from the surface of flashing 26 and provide ventilation of the air space 14 Another benefit of unobstructed ventilating weeps 28 and air spaces is that air pressure is equalized on both sides of the exterior wythe 12 as illustrated in Fig 4 Some design professionals specify installation of additional vents 29 in the upper part of the exterior wythe 12 to provide greater circulation of air through the air space 14 Weeps 28 may be made using a non-woven polymer mesh 27 that is similar to the mesh described for the fluid-conducting medium 20, pre-formed plastic devices, cotton wicking, rope, formed sheet metal components, tubing, perforated tubing, or simply by excluding mortar from the head joints of the bricks 18 comprising the first course of bricks in a wall Weeps 28 and vents 29 are preferably made with non-woven mesh 27 to exclude vermin The non-woven mesh 27 preferred for weeps 28 and vents 29 is preferably more dense than the mesh from which the fluid-conducting medium 20 is made and, in the case of the weeps 28, made using a binder that is resistant to ultra-violet light and photochemical oxidation As with the mesh used for the fluid-conducting medium 20, the mesh used for the weeps 28 and vents 29 will preferably be self-extinguishing and have the following additional properties mildew resistance, fungi resistance, flame spread resistance, and smoke production resistance, The wythes are secured together with steel masonry ties 30 and attachment eyes 32 The masonry ties 30, eyes 32, and horizontal reinforcing 34 and any other steel components used in construction must be kept free of moisture to prevent rust If steel components of masonry construction oxidize, expansion results which can, in turn, cause destructive cracking of masonry and loss of structural integrity In the usual cavity wall 10 construction, an interior wythe 15 is made of concrete block 16 to which board insulation 19 is affixed Sealant 36 is applied to all joints 38 and penetrations 40 of the board insulation 19 including, for example, those made by the masonry ties 30 and eyes 32 The exterior wythe 12 is usually face brick 18 secured in mortar 44 When the brick is laid by the mason, mortar 44 may be expressed from between the bricks The mason removes excess mortar 44 from the exterior of the brick wythe The fluid-conducting medium 20 holds any mortar 44 expressed from between the bricks in its interstices as shown in Fig 7 Mortar 44 and other construction debris is thereby prevented from falling into the cavity air space 14 and obstructing it or the weeps 28 Fig 8 through Fig 22 show a new alternative to the masonry-finished cavity wall system 10 This alternative may be described generally as a trowel-applied cementitious, veneer wall assembly 60 that is finished with stucco 62, EIFS 64 or similar materials Conventional stucco 62 and EIFS 64 walls can be damaged by water penetration when the installation does not provide specific provisions for removing water and venting water vapor to the atmosphere Features of the cavity wall drainage and ventilation system of this disclosure make it possible to improve the performance of the veneer wall assembly 60 Fig 8 shows a veneer wall assembly 60, specifically, a concrete block 16 and stucco 62 wall The wall in Fig 8, unlike previous concrete block 16 and stucco 62 walls, incorporates an air space 14 between the exterior layer made by the stucco 62 and metal lath 66, and the layer made by the framing 17 and board insulation 19 The air space 14 is created and maintained by installing a semi-rigid, partially compressible fluid-conducting medium, or non-woven mat, 68 adapted for use in construction of a veneer wall assembly 60 The framing 17 may be mechanically attached to the concrete block 16 using standard masonry fasteners 70 Board insulation 19 may be press-fit within the metal framing 17 Metal lath 66 is held in place using standard, self-drilling, sheet metal fasteners 74 that connect it to the framing 17 Metal grounds 76 are typically used to provide perimeter termination for the stucco 62 Although other terminations for stucco 62 may be employed, the term metal grounds 76 includes, for the purposes of this disclosure, all stucco 62 terminations The system of the present disclosure provides an additional starter strip 78 at all bottom edges of the stucco 62 installation that receives and secures the metal grounds 76 Fig 17 presents a detail of the starter strip 78 shown in Fig 8 The starter strip 78 can also be inverted to serve with an upper metal grounds 76 to assure that clear openings will be provided to remove moisture and other vapors The starter strip 78 is attached to the concrete block 16 with masonry fasteners 70 and has a channel 80 to secure the bottom edge of the board insulation 19 A drip edge 82 extends downwardly from the bottom surface of the starter strip 78 Weep holes 84 perforate the bottom surface of the starter strip 78 Water that penetrates the exterior finish layer of the veneer wall assembly 60 flows down the board insulation 19 or through the non-woven mat 68 and passes to the outside of the structure through the weep holes 84 that are formed through the web of the channel 80 and through the flange 85 that secures the metal grounds 76 Water is shed from the drip edge 82 onto the metal flashing 88 Additionally, an air infiltration barrier 86 may be installed either adjacent the concrete block 16 or between the non-woven mat 68 and the board insulation 19 In Fig 9, an improved wood frame 17 stucco 62 system is disclosed A vapor barrier 90 may be installed as required by a design professional on either side of the batt or other type of stud space insulation 92 Wood sheathing 94 and cementitious sheathing 96 or gypsum board sheathing 22 may be installed according to the specifications of a design professional to complete the structural wall assembly 98 The term "structural wall assembly" denotes the load- bearing portions of the building wall, collectively, excluding the outermost weather-resistant layers The wood frame embodiment incorporates an air space 14 between the exterior layer made by the stucco 62 and metal lath 66, and the layer made by the cementitious sheathing 96 The air space 14 is created and maintained by installing a non-woven mat 68 Water removal and stucco 62 termination in the wood frame 17 construction shown in Fig 9 is similar to that described and shown in Fig 8 Fig 10 illustrates the incorporation of the present embodiment in a steel frame 17 structure having a stucco 62 veneer wall 60 Vapor barrier 90, air infiltration barrier 86, stud space insulation 92 and sheathing materials may be installed as required by project specifications The metal frame 17 embodiment incorporates an air space 14 between the exterior layer made by the stucco 62 and metal lath 66, and the layer made by the cementitious sheathing 96 The air space 14 is created and maintained by installing a non-woven mat 68 Water removal and stucco 62 termination in the metal frame 17 construction shown in Fig 10 is similar to that described and shown in Fig 8 Fig 1 1 depicts an EIFS 64 veneer wall assembly having a concrete block 16 structural system Board insulation 19 is mechanically attached to the concrete block 16 in accordance with the specification of the EIFS 64 manufacturer In the present embodiment, the non-woven mat 68 is preferably bonded to the exterior side of the board insulation 19 prior to delivery at the construction site Masonry fasteners 70 extend through the board insulation 19 and fastener plates 100 to secure the non-woven mat 68 and the board insulation 19 to the concrete block 16 structural system The fastener plate 100 is corrugated or otherwise shaped to provide secure attachment performance with minimal compression of the non-woven mat 68 Air infiltration 86 and vapor barrier 90 products may be installed in accordance with the specifications of the responsible design professional The mat insulation assembly of the present embodiment would be overlaid by reinforcing fabric 102 made or specified by the EIFS 64 manufacturer It is anticipated that bonding the reinforcing fabric 102 to the non-woven mat 68 opposite the board insulation 19 will improve the adhesion and the tensile strength of the EIFS 64 coatings This improvement will result because the non-woven mat separates the reinforcing fabric 102 from the solid surface of the board insulation 19 and allows the EIFS 64 finish materials to penetrate and completely encapsulate the reinforcing fabric 102 In Direct-Applied Exterior Finish Systems (DEFS), EIFS 64 coatings are normally applied directly to the sheathing material instead of to the board insulation 19 Performance of DEFS may be similarly improved by interposing the non-woven mat 68 between the sheathing and the reinforcing fabric 102 Another method of EIFS 64 construction that is similar to methods currently promoted by manufacturers is set forth in Fig 12 In this method, the non-woven mat 68 is interposed between the concrete block 16 structural system and the board insulation 19 The EIFS 64 materials are applied directly to the board insulation 19 and any reinforcing fabric 102 specified by the manufacturer Board insulation 19 is affixed to the structure with a fastening system 103 specified by the EIFS 64 manufacturer. Vapor barrier 90 and air infiltration 86 aspects of this embodiment are like those described for Fig. 11. Fig. 13 presents a wood framed 17 EIFS 64 veneer wall 60. The wood framing 17 has gypsum sheathing 22. The EIFS 64 materials are applied to the reinforcing fabric 102 and the non-woven mat 68 as described and depicted in Fig. 11. In this embodiment, the non-woven mat 68 is bonded to the board insulation 19 and the reinforcing fabric 102 is bonded to the non- woven mat 68 prior to delivering the insulation to the construction site. The board insulation 19 is affixed to the framing 17 and/or sheathing 22 with fastener plates 100 (shown in detail in Fig. 21) and wood fasteners 104 specified by the EIFS manufacturer. The air infiltration barrier 86 and vapor barrier 90 are shown in suggested locations, but, again, would be installed in accordance with project specifications. The ventilation and drainage system of the EIFS 64 system of the present disclosure provides an architectural shape, preferably an extrusion, to terminate and ventilate the EIFS 64 at the top of the wall and to provide an EIFS starter strip 106 at all bottom edges of the EIFS 64 installation. Top and bottom extrusions may be similar or identical but inverted. Fig. 18 presents a detail of the EIFS starter strip 106 that is attached to the framing 17 with wood fasteners 104. The EIFS starter strip 106 has a channel 80 to secure the bottom edge of the board insulation 19 and a separate mat channel 107 for receiving and securing the non-woven mat 68. A drip edge 82 extends downwardly from the bottom surface of the starter strip 106. Weep holes 84 perforate the bottom surface of the channel 80 and the mat channel 107 of the EIFS starter strip 106. Water flows through the non-woven mat 68 and passes to the outside of the structure through the weep holes 84 and drips from the drip edge 82 away from the foundation 11 or other structural features. Fig. 14 shows a wood framed 17 structure with wood sheathing 94 and cementitious sheathing 96. The features of the wall system of Fig. 14 are like those depicted in Fig. 12 with cement block 16 being replaced with wood framing 17, wood sheathing 94, and cementitious sheathing 96 or gypsum sheathing 22. The board insulation 19 would be overlaid by reinforcing fabric 102 made or specified by the EIFS 64 manufacturer. It is anticipated that locating the non-woven mat 68 between the board insulation 19 and the sheathing will provide superior moisture removal and ventilation compared to systems now known in the art. The board insulation 19 will be omitted in installations such as DEFS. Placing the non-woven mat 68 between the sheathing and the reinforcing fabric 102 is expected to enhance the performance of the DEFS installations in the same way that EIFS performance is improved by increasing ventilation and moisture drainage with the non-woven mat 68 disclosed herein. Fig. 15, summarizes the entire system of the present disclosure by depicting a commonly employed wall assembly in which masonry construction is used on the lower elevations and frame 17 construction with EIFS 64 is used at higher elevations. Economies are achieved by reducing the amount of heavy masonry elements that must be conveyed to elevated areas of the building. The lighter EIFS 64 materials are installed more quickly and easily than is masonry. However, the transition from one construction system to another creates a region with greatly increased likelihood for water penetration. The present embodiment prevents moisture problems with integrated drainage and ventilation systems. Mortar 44 bridging between the brick 18 and the board insulation 19 is prevented by the fluid-conducting medium 20 which holds extruded mortar 44 proximate to the exterior wythe 12. The air space 14 maintained by the fluid-conducting medium 20 communicates with the exterior of the structure through the non-woven polymer mesh 27 that is incorporated in the vents 29. The interior wythe 15 supports the wood or steel framing 17 used with the veneer wall assembly 60. Wood or steel framing 17 terminates the masonry cavity wall 10 with metal flashing 88 at the top . Rain shed from the exterior surface of the veneer wall assembly 60 drips from the EIFS starter strip 106 onto the metal flashing 88, as does water removed from the interior of the EIFS 64 (or stucco 62, not shown) by means of the non-woven mat 68. Wood sheathing 94, gypsum sheathing 22, and stud-space insulation 92 are protected from moisture penetration by the embodiment disclosed herein. As with the descriptions associated with all figures, the air infiltration barrier 86 and the vapor barrier 90 must be provided as required by contract specifications. Fig. 16 shows the embodiment disclosed for the EIFS configuration details of Fig. 12 and Fig. 14 as applied to steel frame 17 building wall assemblies. Fig. 17 shows an isometric detail view of the stucco 62 starter strip 78. Fig. 18 shows an isometric detail view of the EIFS starter strip 106. Fig. 19 shows an isometric detail view of an alternate EIFS starter strip 108 that is adapted for use in installations in which the non-woven mat is situated between the board insulation 19 and the cementitious sheathing 96. The alternate EIFS starter strip 108, like the EIFS starter strip 106 and the stucco 62 starter strip 78, may be inverted and used as a termination strip at the top of the veneer wall assembly 60. The interrelationship of the insulation holding channel 80, the weep holes 84 and the drip edge 82 are more readily seen in Figs. 17-19 than is possible from the section details of Figs. 8-16. Fig. 20 shows the embodiment disclosed for the EIFS configuration details of Fig. 1 , Fig. 13, and Fig. 15 as applied to steel frame 17 building wall assemblies. Fig. 21 shows an isometric detail view of the specially designed fastener plate 100 that is adapted to hold the board insulation 19 equipped with reinforcing fabric 102 and non-woven mat 68 to the various building wall assemblies that incorporate EIFS. Fig. 22 shows, in an isometric detail view, the wall assembly shown in the elevational cross-section of Fig. 15. Fig. 22 shows the generalized configuration that incorporates the component materials comprising the present embodiment. Changes and modifications in the specifically described embodiments can be carried out without departing from the scope of the invention which is intended to be limited only by the scope of the appended claims. INDUSTRIAL APPLICABILITY From the foregoing description, it can be readily seen by those skilled in the art that the methods and articles disclosed have general applicability in the building construction industry. LIST OF DRAWING REFERENCE NUMBERS masonry cavity wall 66 metal lath foundation 68 non-woven mat exterior (or second) wythe 70 masonry fasteners air space 74 self-drilling sheet metal screws interior (or first) wythe 76 metal grounds concrete block 78 starter strip wood or steel framing 80 channel brick 82 drip edge board insulation 84 weep holes fluid-conducting medium 85 flange gypsum board sheathing 86 air infiltration barrier mortar cant 88 metal flashing masonry flashing 90 vapor barrier non-woven polymer mesh 92 stud space insulation weeps 94 wood sheathing vents 96 cementitious sheathing masonry ties 98 structural wall assembly attachment eyes 100 fastener plate horizontal reinforcing 102 reinforcing fabric sealant 103 fastening system joints 104 wood fastener penetrations 106 EIFS starter strip mortar 107 mat channel veneer wall assembly 108 alternate EIFS starter strip stucco EIFS

Claims: CLAIMS I claim: 1. A building wall assembly comprising: a. a first wythe; b. a second wythe; c. an air space between said first wythe and said second wythe; d. means for removing water from said air space; and e. holding means for holding material which enters said air space during construction of said second wythe proximate to the second wythe. 2. The invention according to Claim 1 wherein: a. said holding means is comprised of a fluid-conducting medium through which water and air can flow; b. said holding means substantially fills said air space; and c. said holding means is disposed adjacent and parallel to said second wythe with such spacing for clearance as may be required to accommodate variations in dimensions of the material used in construction of said second wythe. 3. The system for drainage and ventilation of building wall assemblies according to claim 2 wherein the weeps are located near the lowermost level of said exterior wythe. 4. The drainage and ventilation system for building wall assemblies according to claim 3 wherein the vents are located near the uppermost level of the exterior wythe. 5. The system for drainage and ventilation of masonry cavity wall air spaces according to Claim 3 wherein: a. weeps are formed by omitting mortar from a multiplicity of the head joints of the lowermost course of said exterior wythe; b. sections of non-woven, non-absorbent, fluid-conducting mesh substantially fill said weeps. 6. The system for drainage and ventilation of masonry cavity wall air spaces according to Claim 4 wherein: a. vents are created by omitting mortar from a multiplicity of the head joints of the uppermost course of said exterior wythe; b. sections of non-woven, non-absorbent, fluid-conducting mesh substantially fill the vents. 7. The system for drainage and ventilation of masonry cavity wall air spaces according to Claim 4 wherein: a. a continuous vent is created by omitting mortar from the bed joint at the uppermost course of said exterior wythe; b. a section of non-woven, non-absorbent, fluid-conducting mesh substantially fills the vent. 8. The system for drainage and ventilation of masonry cavity wall air spaces according to Claim 5 wherein said non-woven, non-absorbent, fluid-conducting mesh is comprised of polymer fibers and co-polymer binder. 9. The system for drainage and ventilation of masonry cavity wall air spaces according to Claim 6 wherein said non-woven, non-absorbent, fluid-conducting mesh is comprised of polymer fibers and co-polymer binder. 10. The system for drainage and ventilation of masonry cavity wall air spaces according to Claim 7 wherein said non-woven, non-absorbent, fluid-conducting mesh is comprised of polymer fibers and co-polymer binder. 1 1. A system for creating an air space and maintaining drainage and ventilation in a veneer wall assembly, comprising: a. a weather-resistant exterior layer located outside an air space creating, non-woven mat, the non-woven mat being secured to the exterior of a structural wall assembly; b. at least one drainage opening communicating between the air space created by the non-woven mat and the exterior of the veneer wall assembly, said drainage opening being situated near the lowermost level of said air space; c. at least one vent communicating between said air space and the exterior of the veneer wall assembly, the vent being situated near the uppermost level of the air space. 12. The system defined in Claim 11 wherein the veneer wall assembly has an exterior layer made of stucco. 13. The system defined in Claim 12 wherein metal lath overlies the non-woven mat and said metal lath is incorporated into the exterior layer made of stucco. 14. The system defined in Claim 13, further comprising: a. metal grounds terminating the perimeter of the stucco and b. a starter strip attached to the structural wall assembly, the starter strip having; c. a flange to receive and secure the metal grounds, d. a channel to receive and secure board insulation, and e. weep holes through the web of the channel and the flange. 15. The system defined in Claim 11 wherein the veneer wall assembly has an exterior layer made of EIFS coating materials. 16. The system defined in Claim 15 further comprised of insulation disposed between the non- woven mat and the exterior of the structural wall. 17. The system defined in Claim 15 further comprised of insulation disposed between the non- woven mat and the EIFS coating materials. 18. The system defined in Claim 16 further comprised of a structural wall assembly made of concrete block. 19. The system defined in Claim 17 further comprised of a structural wall assembly made of concrete block. 20. The system defined in Claim 16 further comprised of a structural wall assembly made of frame construction and sheathing. 21. The system defined in Claim 17 further comprised of a structural wall assembly made of frame construction and sheathing. 22. The system defined in Claim 16, further comprised of an EIFS starter strip attached to the structural wall assembly, the perimeter of the EIFS being terminated by the EIFS starter strip, the EIFS starter strip being further comprised of: a. a flange flush with the EIFS finish layer, b. a mat channel to receive and secure the non-woven mat, c. a channel to receive and secure the board insulation, and d. weep holes through the web of the mat channel and the web of the channel. 23. The system defined in Claim 17, further comprised of an alternate EIFS starter strip attached to the structural wall assembly, the perimeter of the EIFS being terminated by the alternate EIFS starter strip, the alternate EIFS starter strip being further comprised of: a. a flange flush with the EIFS finish layer, b. a channel to receive and secure board insulation, c. a mat channel to receive and secure the non-woven mat, and d. weep holes through the web of the channel and the web of the mat channel. 24. The system defined in Claim 16 further comprised of reinforcing fabric disposed over the non-woven mat, the reinforcing fabric being secured by a multiplicity of fastener plates. 25. The system defined in Claim 18 further comprised of reinforcing fabric disposed over the non-woven mat, the reinforcing fabric being secured by a multiplicity of fastener plates. 26. The system defined in Claim 20 further comprised of reinforcing fabric disposed over the non-woven mat, the reinforcing fabric being secured by a multiplicity of fastener plates. 27. The system defined in Claim 22 further comprised of reinforcing fabric disposed over the non-woven mat, the reinforcing fabric being secured by a multiplicity of fastener plates. 28. A method for equalizing static pressure within a building wall assembly and the exterior of a building wall comprising the steps of: a. constructing a foundation capable of supporting a first wythe and a second wythe, the wythes being separated by an intermediate air space; b. constructing a first wythe; c. affixing non-woven mat to said first wythe to prevent materials from obstructing said air space; d. constructing a second wythe having a plurality of weeps that communicate between the air space and the exterior of the exterior wythe of said building wall assembly, the weeps being located near the lowermost level of the building wall assembly. 29. A method for draining and ventilating building wall assemblies comprising the steps of: a. constructing a foundation capable of supporting a first wythe and a second wythe, the wythes being separated by an intermediate air space; b. constructing a first wythe; c. affixing holding means to said first wythe to prevent materials from obstructing the air space; d. constructing a second wythe having; i. a plurality of weeps that communicate between the air space and the exterior of the exterior wythe of said building wall assembly, the weeps located near the lowermost level of the air space, and ii. at least one vent communicating between the air space and the exterior of the exterior wythe of the building wall assembly, the vent being situated near the uppermost level of said air space; e. placing a section of non-woven, non-absorbent, fluid-conducting mesh at the weeps to prevent the weeps from becoming obstructed, and; f. placing a section of non-woven, non-absorbent, fluid-conducting mesh at the vent to prevent the vent from becoming obstructed.

Inventors: ATKINS MARK R, ATKINS, MARK, R.
Applicants: ATKINS MARK R, ATKINS, MARK, R.
Application year: 1997
Main classification: E02D19
IPC codes: E04B1