CHANNELIZED RAINSCREEN FRAMEWORK FOR CONSTRUCTION OF CEMENTITIOUS EXTERIOR WALLS

Abstract

A channelized rainscreen framework for making a stucco wall by attaching a back side of the channelized rainscreen framework to a front side of a sheathing of a building and applying mortar to a front side of the channelized rainscreen framework. The channelized rainscreen framework comprising a lath sheet and a channel sheet, the channel sheet having a channel sheet front and a channel sheet back, the channel sheet front coupled to the lath sheet, the channel sheet having alternating troughs and peaks, the troughs and peaks running a length of the channel sheet, the peaks forward of the troughs, the channel sheet defining a plurality of channels behind the peaks. The channel sheet has a plurality of holes sized to allow enough mortar to penetrate through the channel sheet to embed it in the mortar, but not to fill the channels.

Description

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of, and priority to, U.S. Provisional Application No. 61886260 filed on 3 Oct. 2013, incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to building materials. More particularly, the present invention relates to building materials for constructing stucco walls.

BACKGROUND

Stucco as a wall cladding has been used for a long time. Until the 1990s, a stucco wall was typically made by applying cementitious material over metal lath attached to building sheathing (typically plywood or strand board) with building paper as a water resistant barrier in between. The cementitious material will shed some of the water that is thrown on it by the weather, but some water will be absorbed by the cementitious material and when the body of cementitious material is filled to its capacity, some moisture will sit on the inside of the cementitious material against the building sheathing. Also, moisture may be driven inwards through the cementitious material by various forces, including any difference in air pressure that may arise between the exterior of the wall and the inner layers. If there is a sufficient gap between the cementitious material and the water resistant barrier to form a wall cavity, the water will likely drain down and out of the wall. A small gap usually did occur between the cementitious material and older building papers that would allow some drainage. Even so, this gap was not also sufficient to allow complete drainage due to surface tension and unequalized pressure across the cementitious material.

Newer water resistant barrier materials, mostly plastics, have largely displaced the older paper materials. Regardless of the advantages of plastic water resistant barrier materials, they had a disadvantage in that they tended to bond to cementitious materials. With this tendency, no helpful gap appeared between the cementitious material and the water resistant barrier. Water driven through the cementitious material would not drain out, but would accumulate against the water resistant barrier and potentially be driven through it, where it would cause rot of the sheathing material.

The solution to this problem of water accumulation has been to create a rainscreen by forming a cavity between the cementitious material and the water resistant barrier. A rainscreen is defined as an exposed outer skin or surface element of a wall, backed by an air space. The cavity behind the outer skin of the wall is typically created by placing a drainage mat between the cementitious material and the water resistant barrier. Typical drainage mat include corrugated plastic sheets; dimpled plastic sheets; or mats of entangled plastic fibers. The drainage mat partially fills the cavity but has interior passages sufficiently large enough for water to drain down and for air to circulate through. Circulating low humidity air from outside the wall into the wall interior helps remove moisture from the back side of the cementitious material.

To function properly, the rainscreen should be pressure equalized, so that a near zero-pressure difference exists at all times across the rainscreen. A pressure-equalized rainscreen wall design aims to control all forces that can drive water into the wall assembly—air pressure difference, gravity, surface tension, capillary action, and rain drop momentum. Of these, air pressure difference is usually the dominant force with the potential to drive a considerable amount of water into the wall assembly. To ensure adequate pressure equalization and air circulation, the cavity behind the rainscreen must be vented to the exterior of the wall.

If cementitious material were applied directly to the typical drainage mat, the cementitious material would flow into the large interior passages in the drainage mat and block them, preventing drainage and air flow. To prevent this, an additional barrier layer—typically a sheet of tightly woven fabric or non-woven material—is placed between the drainage mat and the cementitious material. This additional barrier increases costs of construction and also slows drying of the cementitious material as it impedes the flow of moisture from the back side of the cementitious material into the cavity behind the rainscreen and prevents direct contact with the air circulating therein.

SUMMARY

Disclosed herein is an exemplary embodiment of a channelized rainscreen framework for making a stucco wall. The channelized rainscreen framework comprises a lath sheet and a channel sheet. The channel sheet has a channel sheet front and a channel sheet back. The channel sheet front is coupled to the lath sheet. The channel sheet has alternating troughs and peaks, with the troughs and peaks running a length of the channel sheet, the peaks forward of the troughs, the channel sheet defining a plurality of channels behind the peaks.

A back side of the channelized rainscreen framework is attached to a front side of a sheathing of a building. Then mortar is applied to a front side of the channelized rainscreen framework, filling a space between the lath sheet and channel sheet with mortar, and covering the lath sheet with mortar. The channel sheet has a plurality of holes sized to allow enough mortar to penetrate through the channel sheet to embed it in the mortar, but not to fill and block the channels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of a channelized rainscreen framework rainscreen back.

FIG. 2 is a sectional view of an exterior wall assembly that includes the channelized rainscreen framework of FIG. 1.

FIG. 3 is a detailed view of one of the channels of FIG. 2.

FIG. 4 is a detailed view of the channel sheet of FIG. 2, showing the interface between the channel sheet and the sheathing.

FIG. 5 is a front view of the exterior wall assembly of FIG. 2.

DETAILED DESCRIPTION

Before beginning a detailed description of the subject invention, mention of the following is in order. When appropriate, like reference materials and characters are used to designate identical, corresponding, or similar components in different figures. The figures associated with this disclosure typically are not drawn with dimensional accuracy to scale, i.e., such drawings have been drafted with a focus on clarity of viewing and understanding rather than dimensional accuracy.

In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals, such as compliance with application and business related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure.

Use of directional terms such as “upper,” “lower,” “above,” “below”, “in front of,” “behind,” etc. are intended to describe the positions and/or orientations of various components of the invention relative to one another as shown in the various Figures and are not intended to impose limitations on any position and/or orientation of any embodiment of the invention relative to any reference point external to the reference.

EXEMPLARY EMBODIMENT

FIG. 1 shows a perspective view of an embodiment of a channelized rainscreen framework 100. The channelized rainscreen framework 100 is designed for use in constructing mortar-based (e.g. stucco or stone façade) exterior wall envelopes that are weather-resistant and provide a means for draining water that enters the exterior wall. The channelized rainscreen framework 100 comprises a lath sheet 102 coupled to a channel sheet 104, with the lath sheet 102 on the front side of the channelized rainscreen framework 100 and the channel sheet 104 on the back side. In the exemplary embodiment, the lath sheet 102 is coupled to the channel sheet 104 with glue, but in other embodiments may be coupled in other ways such as heat bonding or mechanical fasteners. The channelized rainscreen framework 100 is designed to be attached to a building with its backside (i.e., the side with the channel sheet 104) toward the building. Mortar or other cementitious material is then applied to the front side (i.e., the side with the lath sheet 102), filling the space between the lath sheet 102 and channel sheet 104 and covering the lath sheet 102. (See FIG. 2).

The lath sheet 102 is a sheet of material designed to support stucco, mortar or other cementitious material. In the exemplary embodiment, the lath sheet 102 comprises a mesh of lath strands, specifically fiber glass strands, but in other embodiments may be comprised of other suitable materials such as metal, basalt or any composite material.

The channel sheet 104 is shaped with alternating troughs and peaks running down a length of the sheet. The troughs 106 are closer to the back of the channelized rainscreen framework 100 and the peaks 108 are closer to the front. The lath sheet 102 is attached to the front sides of the peaks 108. The boundary between one of the peaks 108 and one of the troughs 106 adjacent to it is a point on the channel sheet 104 that is half way between a farthest forward point on the peak 108 and the farthest rearward point of the trough 106. In the exemplary embodiment, the channel sheet 104 has a trapezoidal profile, with flat portions at the peaks 108, troughs 106 with flat portions wider than the flat portions of the peaks 108 and fairly sharp transitions between the peaks 108 and troughs 106. Other embodiments may have other profiles for channel sheet 104. For example, the profile of the channel sheet 104 may be sinusoid with rounded peaks 108 and troughs 106, or have peaks 108 and troughs 106 that are sharp angled, or may have peaks 108 and troughs 106 that are a combination of sharp angle, rounded, and/or flat.

Channels 120 are defined in the region behind the peaks 108 of the channel sheet 104. The boundaries of one of the channels 120 are the channel sheet 104 and a plane intersecting the rearward-most points on one of the troughs 106 adjacent to the channel 120. The channel 120 provides a path for air to circulate and for water to drain out behind the exterior wall (rainscreen) created when mortar is applied to the channelized rainscreen framework 100.

The channel sheet 104 comprises a sheet of entangled filaments. In the exemplary embodiment, the channel sheet 104 comprises filaments of Polypropylene, but in other embodiments, may comprise filaments of other suitable materials such as nylon. The entangled filaments are numerous, thick and dense enough to almost form a solid sheet, but still leave a large number of holes 134 that penetrate the channel sheet 104. The sizes of the holes 134 vary, because the process of depositing the filaments in a sheet is random. However, the average hole size can be controlled by the mass of filament material deposited per unit area of the sheet. For example, an increased filament material mass per unit area results in a decreased average hole size. Maximum hole size can be controlled by inspection and discarding of sheets exceeding a selected maximum.

The size of the holes 134 in the channel sheet 104 is a significant factor in controlling the flow of mortar applied to the channelized rainscreen framework 100. The channelized rainscreen framework 100 is designed to have mortar applied from the front side, filling the space between the lath sheet 102 and channel sheet 104 and covering the lath sheet 102. The channel sheet 104 is made with holes 134 with an average size sufficiently small so that when typical mortar is applied to the filament sheet front with pressures typically used in mortar application, the mortar will protrude beyond the back of the channel sheet 104 some distance, enough to embed the channel sheet 104 in the mortar, but not enough to fill and block the channels 120. In the exemplary embodiment, the filament material mass per unit area deposited is in the range of 5 to 15 ounces per square yard and maximum hole size is limited to 0.25 inches with most holes smaller than 0.25 inches. This gives good results with mortars typically used in the building industry, allowing some mortar to protrude behind the channel sheet 104 but not enough to block the channels 120. However, channel sheets 104 with other ranges of filament material mass per unit area and hole sizes may be used in other embodiments.

Any point on the lath sheet 102 has a filament sheet depth that is defined as the shortest distance between the lath sheet 102 and the channel sheet 104. The channelized rainscreen framework 100 has a design fraction that is defined as the fraction of points on the lath sheet 102 that have a filament sheet depth that is at least the design filament sheet depth. The design filament sheet depth is based on building code requirements for a depth to which lath must be embedded in mortar and the design fraction is based on a building code requirement for the amount of lath that must be embedded in mortar. In the exemplary embodiment, the channelized rainscreen framework 100 is constructed to have a design filament sheet depth of 0.25 inches and a design fraction of at least 50%. This is because current US building codes require at least 50% of the lath to be embedded in mortar by at least 0.25 inches. However, in other countries the building codes may differ and building codes may change in time, so other embodiments may have different design filament sheet depths and design fractions.

In the exemplary embodiment, the channel sheet 104 has a trapezoidal profile with sharp transitions between peaks 108 and troughs 106. The flat portions of the peaks 108 are 0.25 inches wide and have 1 inch gaps between them. The flat portions of the troughs 106 are 0.75 inches wide and have 0.5 inch gaps between them. Other embodiments may have other profiles and other dimensions for the peaks 108 and troughs 106.

FIG. 2 shows a sectional view of an exterior wall assembly 128 that includes the channelized rainscreen framework 100 of FIG. 1. The channelized rainscreen framework 100 is attached to a sheathing 118 of a building with a plurality of fasteners 110. Preferably, a water resistant barrier 116 is attached to the sheathing 118 between the front side of the sheathing 118 and the back side of the channel sheet 104. Mortar applied to the front of the channelized rainscreen framework 100 forms an inner mortar layer 132 in the region between the lath sheet 102 and the channel sheet 104 and forms an outer mortar layer 130 in front of the lath sheet 102. This application of mortar also forms mortar protrusions 114 into the channel sheet 104 and in some instances, through and into the channels 120 behind the channel sheet 104.

FIG. 3 shows a detailed view of one of the channels 120 of FIG. 2, showing the mortar protrusions 114 in greater detail. The mortar protrusions 114 that penetrate through the channel sheet 104 and into the channels 120 provide several advantages. One advantage is that these mortar protrusions 114 provide additional surface area for water removal. Low humidity air in the channels 120 draw out water directly into vapor. The mortar protrusions 114 provide additional surface area affording more contact between air and cementitious material, accelerating water removal. When the interior part of the cementitious material facing the channels 120 dries, water then migrates from interior parts of the cementitious material and in turn is removed. Another advantage that mortar protrusions 114 provide is the disruption of surface tension. When water is driven into the cementitious material, some moisture will weep out the back side into the channels 120. When sufficient water weeps out in a localized spot, a drop forms, but clings to the wall of the channel 120, held in place by surface tension. The drop grows larger until gravity overcomes the surface tension holding the drop to the wall of the channel 120, causing the drop of water to flow down the channel 120. While the drop is clinging to the sides of the channel 120, migration of water out of the cementitious material is slowed. The irregular shapes of the mortar protrusions 114 disrupt the surface tension of forming drops, causing them to flow away sooner at a smaller size, thereby accelerating the drying of the cementitious material.

FIG. 4 is a detailed view of the channel sheet 104 of FIG. 2, showing the interface between the channel sheet 104 and the sheathing 118. This application of mortar also forms mortar protrusions 114 into the channel sheet 104, but in areas where the channel sheet 104 is adjacent the sheathing 118, the mortar protrusions 114 do not extend through the channel sheet 104 and typically do not extend very far into the channel sheet 104. This happens because when mortar is applied to the channelized rainscreen framework 100, the pressure applied is transmitted through the mortar to the channel sheet 104, compressing it against the sheathing 118 and compressing any air or water trapped between. This compression creates a back force that works to keep the mortar out of the channel sheet 104. Additional, in the exemplary embodiment, the flat portions of the troughs 106 of the channel sheet 104 adjacent the sheathing 118 are denser in filament material than the areas bordering the channels 120. This results in the flat portions of the troughs 106 having holes with a smaller average size than in the portions of the channel sheet 104 adjacent the channels 120. Smaller average hole size will decrease the average depth of mortar penetration into the channel sheet 104. Since mortar does not penetrate much into the channel sheet 104 in the flat portions of the troughs 106, water 126 and air can flow in the cavity space between the inner mortar layer 132 and the sheathing 118.

Higher filament density in the flat portions of the troughs 106 may be a result of deliberate efforts to deposit more filament material in the flat portions of the troughs 106 of the channel sheet 104, or may be an incidental result a simple way of making the channel sheet 104—dropping filament material evenly over a horizontally oriented form for the channel sheet 104. If the form has the desired profile for the channel sheet 104, dropping filament material evenly over the form will naturally result in more material being deposited on horizontal surfaces such as those in the flat portions of the troughs 106 and less on the non-horizontal surface.

FIG. 5 shows a front view of the exterior wall assembly 128 of FIG. 2. The exterior wall assembly 128 has a vent 122 at the top and an exhaust 124 at the bottom. The vent 122 and exhaust 124 penetrate through channelized rainscreen framework 100, the outer mortar layer 130 and inner mortar layer 132 to connect with the channels 120 to create a pressure equalized wall that will maintain near zero pressure differential between the space in front of the exterior wall assembly 128 and the channels 120. This will reduce the driving of water through the outer mortar layer 130 to the inner mortar layer 132. Air can circulate from the outside through the channels 120, removing water in the form of vapor from the inner mortar layer 132. Water 126 in liquid form drains down the channels 120 and out the bottom of the exterior wall assembly 128 through the exhaust 124. The vent 122 and exhaust 124 are configured so that air may enter easily, but rain, especially wind-driven drain cannot enter easily. To accomplish this, the vent 122 and exhaust 124 passage through the exterior wall are typically angled upwards from outside to inside.

It is well known that to adequately relieve dynamic pressure (i.e., pressure that fluctuates quickly with time and location, typically caused by wind), the ratio of the venting area to the volume of the cavity behind the rainscreen must be sufficiently large, so that changes in dynamic pressure due to wind gusts can be quickly relieved. Compared to prior designs with a drainage mat or similar structure, the exterior wall assembly 128 using the channelized rainscreen framework 100 described herein has a smaller cavity volume, which allows the venting area to be smaller. That is, the vent 122 and exhaust 124 may be smaller.

Dynamic pressure on a building façade varies not only with time, but also with its location on the façade. This spatial variation in pressure can induce lateral airflow within the cavity. Standards bodies, such as the National Research Council of Canada recommend dividing the cavity behind the rainscreen at suitable intervals with delimiters that are somewhat impervious to air and properly connected to the rainscreen and to the water resistant/air resistant barrier on the building sheath. The compartmentation of the cavity into smaller air compartments reduces the range of dynamic pressures sustained by each of these compartments, resulting in a better potential for pressure equalization across the rainscreen. Typically, these delimiters are added in with additional materials, such as metal flashing. In the exterior wall assembly 128 using the channelized rainscreen framework 100 described herein separates the cavity behind the rainscreen into channels 120 delimited by the inner mortar layer 132 and the channel sheet 104. As noted above in the discussion of FIG. 4, air can flow through the channel sheet between the inner mortar layer 132 and the sheathing 118, but the gap is small enough that not much lateral airflow is induced. Thus standards for compartmentation of the cavity behind the rainscreen can be met inherently using the channelized rainscreen framework 100 without additional engineering or materials.

Many prior art designs would omit the vent at the top of the wall and only have an exhaust on the bottom of the wall due to concerns about dynamic pressure which would require compartmentalization and vents not just at the top of the wall, but at the top of each compartment as well. This is undesirable from an aesthetic point of view, but primarily undesirable practically as more vents, especially at mid-points up the wall give increase chances for wind-blown rain to get inside the rainscreen. However, omitting the upper vent forgoes the advantage of increased circulation of air through the cavity. The channels 120 that result from using the channelized rainscreen framework 100 are small and narrow, allowing venting standards to be met, but with the vents 122 and exhaust 124 more widely separated than in typical prior designs, allowing the vents 122 to be left in and the advantages of air circulation to be gained.

Those skilled in the art will recognize that numerous modifications and changes may be made to the exemplary embodiment without departing from the scope of the claimed invention. It will, of course, be understood that modifications of the invention, in its various aspects, will be apparent to those skilled in the art, some being apparent only after study, others being matters of routine mechanical, chemical and electronic design. No single feature, function or property of the exemplary embodiment is essential. Other embodiments are possible, their specific designs depending upon the particular application. As such, the scope of the invention should not be limited by the particular embodiments herein described but should be defined only by the appended claims and equivalents thereof.

Claims

1. An article of manufacture comprising;

a lath sheet;

a channel sheet with a channel sheet front and a channel sheet back, the channel sheet front coupled to the lath sheet, the channel sheet having alternating troughs and peaks, the troughs and peaks running a length of the channel sheet, the peaks forward of the troughs, the channel sheet defining a plurality of channels behind the peaks; and

wherein the channel sheet has a plurality of holes having a typical size sufficiently small enough that when mortar is applied to the channel sheet front under typical installation pressure, the mortar will not protrude through the channel sheet enough to block the channels.

2. The article of manufacture of claim 1,

wherein any point on the lath has a channel sheet depth that is a shortest distance between that point and the channel sheet; and

wherein the article of manufacture has a design fraction that is a fraction of points on the lath that have a channel sheet depth that is at least a design channel sheet depth.

3. The article of manufacture of claim 2,

wherein the design channel sheet depth is based on a building code requirement for a depth to which lath must be embedded in mortar; and

wherein the design fraction is based on a building code requirement for an amount of lath that must be embedded in mortar.

4. The article of manufacture of claim 3,

wherein the design channel sheet depth is 0.25 inches and the design fraction is 50%.

5. The article of manufacture of claim 1,

mortar substantially covering the lath and substantially filling a space between the lath and the channel sheet.

6. The article of manufacture of claim 5,

wherein the mortar protrudes slightly beyond the channel sheet creating mortar protrusions into the channels.

7. The article of manufacture of claim 1, further comprising:

wherein the channel sheet has a trapezoidal profile.

8. The article of manufacture of claim 1,

wherein the channel sheet has a sinusoidal profile.

9. The article of manufacture of claim 1,

wherein the channel sheet comprising entangled filaments.

10. The article of manufacture of claim 9,

wherein the channel sheet weighs at least 5 ounces per square yard and n than 15 ounces per square yard.

11. The article of manufacture of claim 1,

wherein the holes in the channel sheet adjacent the channels have a larger average size than in other portions of the channel sheet.

12. An exterior wall assembly comprising;

a sheathing of a building;

a channelized rainscreen framework coupled to a front side of the sheathing, the channelized rainscreen framework comprising a lath sheet and a channel sheet, the channel sheet having a channel sheet front and a channel sheet back, the channel sheet front coupled to the lath sheet, the channel sheet having alternating troughs and peaks, the troughs and peaks running a length of the channel sheet, the peaks forward of the troughs, the channel sheet defining a plurality of channels behind the peaks, wherein the channel sheet has a plurality of holes;

an outer mortar layer in front of the lath sheet; and

an inner mortar layer in a region between the lath sheet and the channel sheet.

13. The exterior wall assembly of claim 12,

wherein the plurality of channels run vertically on the building, providing an open passage for water to drain down between the sheathing and the channel sheet.

14. The exterior wall assembly of claim 12,

wherein the inner mortar layer has protrusion that pass through the plurality of holes in the channel sheet and into the channel.

15. The exterior wall assembly of claim 12,

wherein any point on the lath has a channel sheet depth that is a shortest distance between that point and the channel sheet; and

wherein channelized rainscreen framework has a design fraction that is a fraction of points on the lath that have a channel sheet depth that is at least a design channel sheet depth.

16. The exterior wall assembly of claim 15,

wherein exterior wall assembly of claim 12, the design channel sheet depth is based on a building code requirement for a depth to which lath must be embedded in mortar; and

wherein the design fraction is based on a building code requirement for an amount of lath that must be embedded in mortar.

17. A method for making a stucco wall comprising the steps of;

providing a channelized rainscreen framework comprising a lath sheet and a channel sheet, the channel sheet having a channel sheet front and a channel sheet back, the channel sheet front coupled to the lath sheet, the channel sheet having alternating troughs and peaks, the troughs and peaks running a length of the channel sheet, the peaks forward of the troughs, the channel sheet defining a plurality of channels behind the peaks, wherein the channel sheet has a plurality of holes;

attaching a back side of the channelized rainscreen framework to a front side of a sheathing of a building; and

applying mortar to the a front side of the channelized rainscreen framework.

18. The method of claim 17, wherein the step of apply mortar further comprises the steps of:

filling a space between the lath sheet and channel sheet with mortar; and

covering the lath sheet with mortar.