Patent Application
20150096247
The present invention relates to building materials. More particularly, the present invention relates to building materials for constructing stucco walls.
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.
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.
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.
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.
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.
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
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.
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.
| Number | Date | Country | |
|---|---|---|---|
| 61886260 | Oct 2013 | US |
