Patent Application
20090158683
1. Field of the Invention
The present invention relates to a building wrap for wrapping the structural components of a building in order to protect the structural components and optional building sheathing from moisture.
2. Description of the Related Art
Two sheets of a water resistive barrier (“WRB,” also commonly referred to as “weather-resistive barrier” or “house wrap”) material are known for use as a building wrap under facade materials such as three-coat stucco or traditional Portland cement which are applied wet, e.g., using a trowel or by spraying. For instance, such building wraps can include two layers of Grade D building paper, two layers of asphalt-saturated kraft paper, two layers of building felt, two layers of a conventional polymeric house wrap, or one layer of building paper combined with one layer of polymeric house wrap. Known polymeric house wraps for use as WRBs include, for example, spunbond polyethylene sheet available under the trade name Tyvek® from E. I. du Pont de Nemours & Co., Wilmington, Del. (“DuPont”); polyolefin nonwoven sheet available under the trade name Styrofoam™ Weathermate™ Plus from The Dow Chemical Company, Midland, Mich.; spunbonded polypropylene-microporous film laminate available under the trade name Typar® Weather Protection Membrane from Fiberweb, London, UK; woven polypropylene sheet with a perforated coating available under the trade name Pinkwrap® from Owens Corning, Corning, N.Y.; and coated nonwoven sheet available under the trade name WeatherSmart™ from Fortifiber Building Systems Group, Reno, Nev. The space between the two layers provides a drainage space for any liquid water that penetrates the outer layer.
Also known is the use of a layer of water resistive barrier combined with a layer of a three-dimensional mesh through which water may drain. The mesh layer of these systems allows the wet-applied stucco to penetrate the mesh, thereby interfering with the drainage of liquid water through the mesh and inhibiting the transport of moisture vapor through the water resistive barrier.
Currently, the International Building Code®, published by International Code Council, requires the use of “weather-resistant barriers” behind stucco facades as follows:
It would be desirable to have an alternative multiple sheet building wrap available for use under wet-applied stucco that would retain good drainage of liquid water, moisture vapor permeability and that would protect the underlying building structure from the penetration of liquid water, and an economical process for installing such a building wrap.
The present invention is directed to a multiple sheet building wrap for wrapping the structural components and optional sheathing of a building in order to protect the structural components and optional sheathing from moisture, the sheet comprising:
In another embodiment, the present invention is directed to a process of wrapping the structural components and optional sheathing of a building in order to protect the building structure from moisture comprising wrapping the structural components and optional sheathing of the building with the multiple sheet building wrap.
In yet another embodiment, the present invention is directed to a multiple sheet building wrap as described above, further comprising a lath layer adjacent the intervening layer, wherein the water resistive barrier, the intervening layer and the lath layer are attached.
In yet another embodiment, the present invention is directed to an external wall assembly of a building utilizing the multiple sheet building wrap as described above.
The terms “nonwoven fabric”, “nonwoven sheet”, “nonwoven layer”, and “nonwoven web” as used herein refer to a structure of individual strands (e.g. fibers, filaments, or threads) that are positioned in a random manner to form a planar material without an identifiable pattern, as opposed to a knitted or woven fabric. The term “fiber” is used herein to include staple fibers as well as continuous filaments. Examples of nonwoven fabrics include meltblown webs, spunbond nonwoven webs, flash spun webs, staple-based webs including carded and air-laid webs, spunlaced webs, and composite sheets comprising more than one nonwoven web.
The term “plexifilamentary” as used herein, means a three-dimensional integral network or web of a multitude of thin, ribbon-like, film-fibril elements of random length and with a mean film thickness of less than about 4 micrometers and a median fibril width of less than about 25 micrometers. In plexifilamentary structures, the film-fibril elements are generally coextensively aligned with the longitudinal axis of the structure and they intermittently unite and separate at irregular intervals in various places throughout the length, width and thickness of the structure to form a continuous three-dimensional network. A nonwoven web of plexifilamentary film-fibril elements is referred to herein interchangeably as a “flash spun plexifilamentary sheet” and a “plexifilamentary film-fibril sheet.” Examples of plexifilamentary film-fibril structures are flash-spun polyolefin sheet sold under the trade name DuPont™ Tyvek® HomeWrap® and DuPont™ Tyvek® StuccoWrap® by E. I. du Pont de Nemours and Company (Wilmington, Del.).
The term “water-resistive barrier” (also referred to herein as “WRB”) refers to a material behind an exterior wall covering of a building that resists liquid water that has penetrated behind the exterior covering from further intruding into the exterior wall assembly. As defined herein, a WRB is capable in its as-received condition (i.e., not subjected to weathering) of meeting the water resistance, moisture vapor permeability and strength requirements of Acceptance Criteria for Water-Resistive Barriers AC38 (effective date Jul. 1, 2004), published by ICC Evaluation Service, Inc., Whittier, Calif.
The present invention relates to a multiple sheet building wrap for wrapping the sheathing or structural components of a building in order to protect the sheathing or structural components from liquid water penetration, especially for use in buildings having wet-applied facades such as traditional three-coat stucco or engineered stone. The multiple sheet building wrap of the invention is moisture vapor permeable so that any moisture on the interior of the building wrap, e.g., moisture contacting the sheathing or structural components wrapped by the building wrap, is permitted to dry.
According to one embodiment of the invention, the multiple sheet building wrap has a moisture vapor permeable WRB layer and a liquid permeable intervening layer, and a three-dimensional mesh layer disposed therebetween. The mesh layer provides a drainage space between the WRB layer and the intervening layer. Liquid water which may penetrate from the exterior of the wall assembly through the intervening layer is directed by the WRB to drain vertically through mesh layer as a result of gravity to the lowermost portion of the wall assembly where it is directed to the exterior of the building. The layers of the building wrap do not absorb moisture, facilitating drying through diffusion. The capacity of the building wrap of the invention for drainage and drying make it particularly well suited for use with wet-applied facade materials, aiding in the curing so that the resulting facade has good flexural strength and reducing the incidence of shrinkage cracking.
The intervening layer (also referred to as “IL”) of the building wrap acts as a filter layer, not allowing significant penetration of stucco therethrough. Stucco penetration is undesirable as it hinders liquid water drainage and moisture vapor permeability of the building wrap. The degree of penetration of stucco through the IL depends on the porosity of the IL material, the size of the particles in the stucco mixture, and the pressure at which the stucco is applied.
WRB layers suitable for use in the building wrap of the invention are capable in its as-received condition (i.e., not subjected to weathering) of meeting the water resistance, moisture vapor permeability and strength requirements of Acceptance Criteria for Water-Resistive Barriers AC38 (effective date Jul. 1, 2004), published by ICC Evaluation Service, Inc., Whittier, Calif. The WRB layer is permeable to moisture vapor, having an average moisture vapor transmission rate of at least 35 g/m2 per 24 hours.
Suitable moisture vapor permeable WRBs for use as the WRB layer of the multiple sheet building wrap include porous sheets, which include woven fabrics, such as sheets of woven fibers or tapes, or nonwoven fabrics, such as flash-spun plexifilamentary sheets, spunbond nonwoven sheets, spunbond-meltblown nonwoven sheets, spunbond-meltblown-spunbond (SMS) nonwoven sheets, asphalt-saturated papers, felts and laminates of any of the above including laminates of nonwoven or woven fabrics or scrims and a moisture vapor permeable film such as microporous film, microperforated film or nonporous breathable film. The WRB layer can comprise a coated sheet, such as sheets used in the construction industry including sheets of woven tapes that have been coated with a polymeric film layer and microperforated.
Microporous films are well known in the art, such as those formed from a mixture of a polyolefin (e.g., polyethylene) and fine particulate fillers, which is melt-extruded, cast or blown into a thin film and stretched, either mono- or bi-axially to form irregularly shaped micropores which extend continuously through the thickness of the film. U.S. Pat. No. 5,955,175 discloses microporous films, which have nominal pore sizes of about 0.2 micrometer. Microporous films can be laminated to nonwoven or woven layers using methods known in the art such as thermal or adhesive lamination.
Microperforated films are formed by casting or blowing a polymer into a film, followed by mechanically perforating the film, as generally disclosed in European Patent Publication No. EP 1 400 348 A2, which indicates that the microperforations are typically on the order of 0.1 mm to 1.0 mm in diameter.
In one embodiment, the moisture vapor permeable sheet is a flash spun plexifilamentary polyolefin sheet such as Tyvek® flash spun high density polyethylene, available from E. I. du Pont de Nemours and Company (Wilmington, Del.). Suitable flash spun plexifilamentary film-fibril sheet materials may also be made from polypropylene. The moisture vapor permeable sheet can be a laminate of a flash spun plexifilamentary sheet with one or more additional layers, such as a laminate comprising a flash spun plexifilamentary sheet and a melt-spun spunbond sheet. Flash spinning processes for forming web layers of plexifilamentary film-fibril strand material are disclosed in U.S. Pat. No. 3,081,519 (Blades et al.), U.S. Pat. No. 3,169,899 (Steuber), U.S. Pat. No. 3,227,784 (Blades et al.), U.S. Pat. No. 3,851,023 (Brethauer et al.), the contents of which are hereby incorporated by reference.
The moisture vapor permeable WRB for use in the invention can be a low emissivity, breathable house wrap or a rooflining product having a metallized surface, such as those described in U.S. patent application Ser. No. 10/924,218.
The multiple sheet building wrap of the invention includes a layer of three-dimensional mesh adjacent the WRB layer, disposed between the WRB and intervening layers. The mesh layer has sufficient porosity so that liquid water is allowed to readily pass or drain through the mesh layer. A suitable three-dimensional mesh layer can have a thickness between about 0.32 cm and about 0.63 cm. If the mesh layer is thinner, drainage is not facilitated. If the mesh layer is thicker, the building wrap is too bulky particularly around fenestration such as doors and windows. The mesh layer advantageously has good strength, flexibility and compressibility in order to absorb energy during stucco application.
Suitable materials for use as the mesh layer include three-dimensional mats of entangled polymeric filaments such as, for example, Enkamat® 5006 and Enkamat® 7004 nylon mats commercially available from Colbond (Enka, N.C.). Other suitable materials include three-dimensional mats sold for use as air filtration media.
The multiple sheet building wrap of the invention additionally includes a porous, liquid permeable intervening layer adjacent the mesh layer. The intervening layer is permeable to moisture vapor and to liquid water so that if liquid water comes into direct contact with the intervening layer, it will readily pass through the thickness of the intervening layer and drain through the mesh layer disposed between the WRB and the IL.
The pore size of the intervening layer is such that liquid water penetrates the intervening layer, but wet-applied facade materials such as wet stucco do not penetrate through the intervening layer when applied to a lath layer installed adjacent to and external to the intervening layer. Stucco may adhere to or embed itself in the intervening layer, but for proper functioning of the building wrap of the invention, stucco should not penetrate entirely through the thickness of the intervening layer. The intervening layer should have sufficient abrasion resistance to prevent tearing of the intervening layer by manual application of stucco.
Suitable intervening layers include asphalt-saturated papers, felts, woven fabrics, woven tapes, flash-spun plexifilamentary sheets, spunbond nonwoven sheets, spunbond-meltblown nonwoven sheets, spunlaid nonwoven sheets and spunbond-meltblown-spunbond nonwoven sheets. Specific examples include spunbond polypropylene sheets sold under the trade name Typar® by E. I. du Pont de Nemours & Co. (Wilmington, Del.), Typar® by BBA Fiberweb (Old Hickory, Tenn.), and spunlaid bicomponent nonwoven sheets sold under the trade name Colback® by Colbond (Enka, N.C.). The intervening layer is preferably a nonabsorbent material so that moisture does not become trapped within the building wrap of the invention.
The WRB, mesh and intervening layers are either not attached to each other, or they are attached in a discontinuous manner such that they are not continuously adhered over significant surface area. Advantageously, if the three layers are attached, they are attached by a nonpermanent means, including by means of adhesive strips, adhesive spots, or spot welding or ultrasonic bonding in a discrete pattern. The WRB, mesh and intervening layers can be attached to each other; alternatively the WRB and the intervening layers can be attached with the mesh layer disposed unattached therebetween.
The intervening layer has a hydrostatic head of less than 51 cm of water, even less than 10 cm of water, even less than 6 cm of water. The intervening layer is porous, having a maximum pore size of between about 20 micrometers and about 750 micrometers, even between about 30 micrometers and about 500 micrometers, and even between about 70 micrometers and about 370 micrometers.
Advantageously, the multiple sheet building wrap is durable when exposed to UV radiation, extreme temperatures and repeated exposure to water. The WRB, mesh and intervening layers may be formed from a variety of polymeric compositions. For example, sheets used in the construction industry are typically formed from polyolefins such as polypropylene or high density polyethylene, polyesters, or polyamides.
According to another embodiment of the invention, the multiple sheet building wrap includes a moisture vapor permeable WRB, a mesh layer and an intervening layer, as described herein, further including a layer of lath material attached to the intervening layer. The lath material can be any flexible material capable of holding and supporting stucco or other wet-applied facade material. This embodiment allows the multiple sheet building wrap and the lath to be conveniently and economically installed together in one step.
In the non-limiting examples that follow, the following test methods were employed to determine various reported characteristics and properties. ASTM refers to the American Society of Testing Materials. ISO refers to the International Standards Organization. TAPPI refers to Technical Association of Pulp and Paper Industry.
Stucco Penetration Test was used to rate the degree of penetration of stucco through samples of building wrap when the stucco is applied either manually using a trowel or a mechanical stucco gun.
The stucco mixtures used are prepared generally according to ASTM C926-98A.
The stucco is applied onto samples mounted on vertical test wall sections (construction method described below) at an ambient temperature above 40° F. A single coat of stucco is applied on the samples at a thickness of ⅜ in (0.95 cm). Each sample is then inspected for stucco penetration and given a numeric rating according to the following rating scale system.
The construction method for each test wall section is described as follows. Seven 2 in×4 in (5 cm×10 cm) wood studs are aligned vertically and spaced about 14.5 inches (37 cm) apart to form an 8 foot×8 foot (2.4 m×2.4 m) wall section. A 2 in×4 in wood stud is attached horizontally along the top and bottom of the wall section to brace each wall section.
Oriented strand board (OSB) sheathing is mounted on the wall section. A matrix of building wrap samples is created on an 8 foot×8 foot (2.4 m×2.4 m) sheet of DuPont™ Tyvek® HomeWrap® by taping samples 16 in wide by 12 in high onto the Tyvek®. The Tyvek® sheet/sample matrix is mounted on the 8 foot×8 foot (2.4 m×2.4 m) test wall section using a nail at each corner. Staples are used to anchor the samples onto the OSB. Once the samples are secured on the walls, stucco is applied. The Tyvek® sheet/sample matrix is then removed and the samples removed from the Tyvek® sheet whereupon the back of the IL and the mesh layer 10 were inspected to determine the degree of stucco penetration.
Moisture Vapor Transmission Rate (MVTR) is measured according to ASTM E-96 (Methods A and B).
Pore Size is measured using the Capillary Flow Porometer method and follows ASTM F316-86 and F778.
The following intervening layers and mesh layers in combination with DuPont™ Tyvek® HomeWrap® (E. I. du Pont de Nemours & Co., Wilmington, Del.) as the WRB layer were tested for stucco penetration. Control samples did not include a mesh layer. Building wraps which received a stucco penetration rating of greater than 5 were deemed to be suitable for use as building wrap. As can be seen from Table 1, acceptable stucco penetration was obtained in all of the following example combinations and not in the control samples.
The slump level of the stucco is an indication of the moisture content of the stucco mixture, as determined by ASTM C143.
