US20120011792A1

US20120011792A1 - High strength light-framed wall structure

Info

Publication number: US20120011792A1
Application number: US13/179,583
Authority: US
Inventors: Dean P. DeWildt; Gregory S. Bergtold
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-07-15
Filing date: 2011-07-11
Publication date: 2012-01-19
Also published as: CA2746305A1

Abstract

A light-framed wall structure contains a wall frame of studs, a bottom plate and a single top plate that together define a stud cavity; exterior sheathing attached to the wall frame and covering the stud cavity; and a polyurethane foam within the stud cavity and affixed to the exterior sheathing, studs, bottom plate and top plate.

Description

CROSS REFERENCE STATEMENT

This application claims the benefit of U.S. Provisional Application No. 61/364,413, filed Jul. 15, 2010, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a light-framed wall structure, a process for making the light-framed wall structure and a building containing the light-framed wall structure.
2. Description of Related Art
There is a continuous drive in the building industry to decrease building costs while increasing thermal insulating properties and maintaining structural integrity under building codes. Wall framing members are one type of building element that plays a role in all aspects of this drive. The large number of framing members in a light-framed wall structure inherently makes them a notable contributor to the building cost. Framing members also have a relatively low insulation value and serve as a means for thermal shorts through a wall structure since insulation is often applied only between the framing members. From a cost and insulation perspective, it would be desirable to reduce the number of framing members in a light-framed wall structure.
However, building codes specify that wall structures must meet certain structural integrity criteria. In particular, a wall in a building structure must withstand lateral and transverse loads resulting from wind and earthquakes as well as axial loads due to structure weight, snow, and floor loads. The International Residential Building Code (IRC) and International Building Code (IBC) provide prescriptive solutions and minimum standards for walls that meet code structural integrity criteria. The prescriptive solutions commonly utilize 2×4 studs spaced 16-inch on center, or 2×6 studs spaced 24-inches on center, with a double top plate over the studs to distribute axial point loads. Additionally, the IRC and IBC allow for a single top plate provided that roof rafters or floor joists align within one inch of stud centerlines so as to directly transfer their load to a stud below. While such a wall design reduces building elements by using a single top plate, the necessary careful alignment of roof rafters or floor joists reduces flexibility in building designs and construction. The IRC and IBC allow for custom engineered wall designs provided the wall has sufficient load bearing properties.
It is desirable to develop a light-framed wall structure that can support axial point, transverse and lateral loads sufficiently to meet IRC and IBC requirements for structural integrity but by using fewer framing members, especially if such a wall structure requires only a single top plate and alignment of second floor studs and/or roof rafters and trusses did not have to align within one inch of the wall structure studs. Even more desirable is such a light-framed wall structure that would eliminate the problem of thermal shorts through the wall caused by the studs by including an insulating layer that extends over the studs.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a solution to the desire for a light-framed wall structure that can support axial point, transverse and lateral loads sufficiently to meet IRC and IBC requirements for structural integrity with fewer framing members and in particular such a wall structure requiring only a single top plate where alignment of second floor studs and/or roof rafters and roof trusses do not have to align within one inch of the wall structure studs. Even more, the present invention can provide a light-framed wall structure that eliminates thermal shorts through the wall caused by the framing elements by including an insulating layer that extends over the studs.
Surprisingly, the objectives of the present invention are achievable with a stud spacing in a range of nominally 16 inches to nominally 24 inches on center, even when using a single top plate, sheathing overlaying the studs and spanning the spacing between the studs and the presence of polyurethane foam disposed in the stud cavity adhering to the studs and the sheathing.
Light-framed wall structures of the present invention surprisingly can concomitantly support (that is, withstand; resist without failure) axial point loads of 2500 pounds or more, even 3500 pounds or more, and even 4000 pounds or more (and desirably uplift loads of 1500 pounds or more even 2000 pounds or more) according to ASTM method E72, Section 9 as modified in the Example below (exclusion of the I-beam along the top plate); lateral loads of 500 pounds per linear foot (plf) or more, even 750 plf or more, and even 1000 plf or more according to ASTM method E72, Section 14; and transverse loads of 150 pounds per square foot (psf) or more, even 200 psf or more, and even 250 psf or more according to ASTM method E72, Section 11.
In a first aspect, the present invention is a light-framed wall structure comprising: (a) studs spaced apart from one another in a range of nominally 16 to nominally 24 inches on center; (b) a bottom plate and a single top plate spanning the studs and attached to opposing ends of the studs such that the studs, top plate and bottom plate define a wall frame having opposing interior and exterior surfaces with the studs, top and bottom plate further defining a stud cavity within the wall frame, the stud cavity having a height extending from bottom plate to top plate and a width extending from one stud to another stud; (c) sheathing spanning the width and height of the stud cavity and overlapping the studs and attached to at least one of the exterior and interior surfaces of the wall frame; and (d) polyurethane foam forming a seal around the inside perimeter of the stud cavity and affixed to the sheathing material on at least one surface of the wall frame, the stud, top plate and bottom plate where the polyurethane foam extends at least 1.5 inches over the sheathing, studs, top plate and bottom plate along the perimeter and further is present at an average thickness of at least 3.5 inches over the volume of the stud cavity within six inches of the top plate; wherein the light-framed wall structure is free of metal corner connectors or reinforcements comprising a box-shaped section against which the studs, bottom plate and top plate abut.
In a second aspect, the present invention is a light-framed wall structure comprising: (a) studs nominally spaced apart from one another 24 inches on center; (b) a bottom plate and a single top plate spanning the studs and attached to opposing ends of the studs such that the studs, top plate and bottom plate define a wall frame having opposing interior and exterior surfaces with the studs, top and bottom plate further defining a stud cavity within the wall frame, the stud cavity having a height extending from bottom plate to top plate and a width extending from one stud to another stud; (c) exterior sheathing spanning the width and height of the stud cavity and overlapping the studs and attached to the exterior surface of the wall frame; and (d) polyurethane foam within the stud cavity and affixed to the exterior sheathing material, studs, top plate and bottom plate defining the stud cavity, the polyurethane foam having an average thickness of at least 0.5 inches within the stud cavity; wherein the light-framed wall structure is free of metal corner connectors or reinforcements comprising a box-shaped section against which the studs, bottom plate and top plate abut.
In a third aspect, the present invention is a process for making the light-framed wall structure of the first aspect, the process comprising the following steps: (a) assembling studs nominally spaced 24 inches on center between a single top plate and a bottom plate so as to form a wall frame having opposing interior and exterior surfaces and defining a stud cavity between the studs and top and bottom plates and affixing the studs to the top and bottom plates; (b) affixing exterior sheathing to the exterior surface of the wall frame over the studs and stud cavity; and (c) disposing a polyurethane foam into the stud cavity onto the exterior sheathing and against the studs and top and bottom plates so as to have an average expanded thickness of at least 0.5 inches within the stud cavity and so that the polyurethane foam attaches to the exterior sheathing, studs and top and bottom plates of the stud cavity.
In a fourth aspect, the present invention is a building structure comprising the light-framed wall structure of the first aspect.
The light-framed wall structure and process of the present invention is useful in constructing buildings. The building of the present invention is useful as a building structure for many types of use including residential housing and light commercial buildings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of the light-framed wall structure of present invention with FIG. 1(A) illustrating a cutaway view looking down from the top from under the top plate and FIG. 1(B) illustrating a view from the interior surface side.

FIG. 2 illustrates an embodiment of the light-framed wall structure of the present invention illustrating a view from the interior surface side.

DETAILED DESCRIPTION OF THE INVENTION

“ASTM” refers to American Society for Testing and Materials and is used to designate a test method by number as published by ASTM. Test numbers refer to the most recent test published prior to the priority date of this document unless otherwise specified by a date using a hyphenated suffix after the test number.
“Multiple” means two or more. “And/or” means “and, or as an alternative”. All ranges include endpoints unless otherwise indicated.
“Length”, “width” and “thickness” are three mutually perpendicular dimensions of an object. Length is a dimension having a magnitude equivalent to the largest magnitude dimension of the length, width and thickness. Thickness has a magnitude equal to the smallest magnitude of the length, width and thickness. Width has a magnitude equal to the length, thickness, both the length and thickness, or a magnitude somewhere between that of the length and thickness.
“Light-framed wall structure” refers to a wall structure comprising studs spaced apart from one another and attached at opposing ends to top plate and bottom plate members. The studs, top plate and bottom plate define a wall frame that defines stud cavities between studs and the top and bottom plates.
“Polyurethane foam” refers to a polymeric foam wherein the polymeric matrix of the foam comprises polyurethane linkages formed by reacting isocyanate functionalities with polyol and/or other reactive additives. The polyurethane foam has an isocyanate index in a range of 95 or higher, preferably 100 or higher, still more preferably 120 or higher and yet more preferably 150 or higher. At the same time the isocyanate index is desirably 350 or lower, preferably 300 or lower, more preferably 250 or loser and yet more preferably 200 or lower. Determine isocyanate index by multiplying 100 times the actual amount of isocyanate used divided by the theoretical amount of isocyanate required to stoichiometrically react with all of the polyol and other isocyanate-reactive additives in the foam formulation.
In one aspect the present invention is a light-framed wall structure. In the light-framed wall structure of the present invention the studs are spaced apart nominally 16 to 24 inches on center. Particularly common spacings suitable for use in the present invention include nominally 16 inches on center, nominally 19.2 inches on center and nominally 24 inches on center. “Nominal” values include tolerances from the specific value that are commonly accepted in the construction industry. For example, actual spacing can be off from a nominal value by as much as 0.125 inches or less, preferably 0.0625 or less, more preferably 0.0312 inches or less from being spaced exactly the nominal value. Spacing “on center” refers to a measurement taken from the center of one stud to the center of the next neighboring stud. Typically, studs are aligned such that the surface of one stud faces the surface of another stud and the distance on center is measured from the center of the thickness (center of an edge) of one stud to the center of the thickness (center of an edge) on a neighboring stud.
Studs can be any stud known or yet to be used in constructing light-framed wall structures. Suitable studs include what is commonly known as 2×4 and/or 2×6 dimensional building elements, where the numbers designate the nominal thickness and width of the building elements in inches rounded up to the nearest inch. Typically, 2×4 elements are nominally 1.5 inches thick and nominally 3.5 inches wide and 2×6 elements are nominally 1.5 inches thick and nominally 5.5 inches wide. Often studs are made from lumber (wood) or metal (typically, thin gauge steel). Studs, as well as top and bottom plates, have opposing surfaces, edges and ends. The width of a stud and bottom plate separates opposing edges, thickness separates opposing surfaces and length separates opposing ends.
The light-framed wall structure of the present invention is further characterized by having a bottom plate and a single top plate, each spanning multiple studs. Bottom plates and top plates can be any currently known or yet to be developed material for light-framed wall structures. As with the studs, the bottom plate and top plate are often dimensional building elements such as 2×4 or 2×6 materials. It is common to use dimensional building elements of the same thickness and width for the top plate, bottom plate, or both top plate and bottom plate as is used for the studs they span. It is also common to use top and bottom plates made of the same material as the studs they span.
As the name suggests, bottom plates and top plates span the bottom and top of the studs, respectively, to form the wall frame of the light-framed wall structure. Studs have one of their ends attached to a surface of a bottom plate and their opposing end attached to a surface of a top plate. It is common to attach the studs to the top and bottom plates using nails (for example, steel nails) when the building elements are wood and screws or pins when the building elements are metal. In such a configuration, neighboring studs and the top and bottom plates spanning those studs define a stud cavity having a height extending from the bottom plate to the top plate (the length of the studs) and a width extending from one stud to a neighboring stud. It is common for the studs to have an orientation in the light-framed wall structure such that the surface of one stud faces the surface of a neighboring stud and the facing surfaces are both exposed within a stud cavity. At the same time, one of the edges of each stud (the inside edge) is on what shall be called the “interior” surface of the wall frame and the opposing edge of the stud (the outside edge) is on what shall be called the “exterior” surface of the wall frame. Similarly, a surface of the top plate faces a surface of the bottom plate and both of these facing surfaces are exposed within a stud cavity while one of the edges of each of the top and bottom plates is on the interior surface of the wall frame and the opposing edge is on the exterior surface of the wall frame.
The wall frame achieves sufficient strength without requiring metal corner connectors having box-shaped intermediate sections as taught in U.S. Pat. No. 7,882,666 ('666). Reference '666 discloses a prefabricated building component that comprises a frame of lumber components in a rectangular orientation and joined together with metal corner connectors. Each corner connector comprises a metal box against which the lumber components abut. These corner reinforcements are necessary components of the '666 structure. However, the present invention is free of metal corner connector having box-shaped intermediate sections against which the studs, top plate and bottom plate abut. Applicants have discovered a method of achieving suitable strength, particularly racking strength, with the wall structure of the present invention without requiring such metal corner reinforcements.
As noted, the wall frame has a stud cavity defined therein. While teachings, including descriptions and claims, herein generally refer to “a” stud cavity defined within a wall frame by studs, top and bottom plates, the wall frame can and typically does have multiple stud cavities defined by the studs, top and bottom plates of the wall frame. The wall frame of the light-framed wall structure of the present invention can have defined therein one or more than one stud cavity (that is, reference to “a” stud cavity does not imply there is only a single stud cavity in the wall frame). Teachings herein, when referring to “a” stud cavity, can and desirably do apply to more than one and most desirably apply to each stud cavity in a wall frame of the light-framed wall structure when the light-framed wall structure has multiple stud cavities defined therein. For example, teaching that exterior sheathing fully covers the stud cavity should be understood as meaning exterior sheathing preferably fully covers multiple stud cavities if the wall frame contains more than one stud cavity, and more preferably covers each stud cavity of the wall frame. Similarly, teaching about polyurethane within a stud cavity should be understood as desirably being applicable to multiple and preferably each stud cavity of the wall frame when the wall frame contains more than one stud cavity.
Wall frames can also have defined therein sub-cavities within a stud cavity. A sub-cavity is a portion of a stud cavity that does not extend from a base plate to a top plate. For example, headers and sills extending from one stud to a neighboring stud divide a stud cavity into multiple sub-cavities for framing a window into a wall frame. One of the sub-cavities is sized to accommodate the window and is not filled with polyurethane foam or covered with exterior or interior sheathing. However, the sub-cavities that are typically above and/or below the window are desirably treated as described herein for a stud cavity in the present invention—that is, the sub-cavities are covered with sheathing and polyurethane foam disposed within the sub-cavity and, generally, enclosed with both exterior and interior sheathing. In like manner, framing for a door in a wall frame can result in creation of separate sub-cavities of a stud cavity, one to fit the door and the other to be desirably treated in like manner as a cavity of the present invention. It is desirable to treat sub-cavities as stud cavities according to the teachings herein in order to achieve an optimally insulated and reinforced wall structure of the present invention, except for those sub-cavities that accommodate a functional component such as a door or window.
The light-framed wall structure of present invention comprises sheathing that spans the width and height of the stud cavity thereby covering (typically, entirely covering) the stud cavity and overlapping the studs of the wall frame. The sheathing overlaps and attaches to edges of the studs on a surface of the wall frame. The sheathing can be exterior sheathing attached to the exterior surface of the wall frame, interior sheathing attached to the interior surface of the wall frame, or the light-framed wall structure can comprise both exterior and interior sheathing attached to their corresponding surfaces of the light-framed wall. It is desirable that the light-framed wall structure comprise at least exterior sheathing. Exterior sheathing serves as a protective barrier from outside elements and can further serves as thermal insulation as well as structural reinforcement
Suitable sheathing includes panels of foam sheathing (for example, polymeric foam board that can comprise facer material on one or more than one surface or that is free of facer material), wood sheathing (for example, oriented strand board or plywood), fibrous structural board (for example, fiberboard), composite structures such as structural insulated sheathing, gypsum board, or paneling of any composition. Typically, exterior sheathing is selected from foam sheathing, wood sheathing, fibrous structural board, gypsum board and composition structures such as structural insulated sheathing. Typically, interior sheathing is selected form gypsum board and paneling. Gypsum board refers to what is also known as drywall or plasterboard.
Desirably, the present invention includes exterior sheathing. Even more desirably, the exterior sheathing simultaneously increases structural integrity, barrier properties and thermal insulation to the light-framed wall structure. In that regard, particularly desirable exterior sheathing comprises an insulating foam element and a structural sheathing element such as wood sheathing or fibrous sheathing in a single product that can be applied onto a wall frame in a single step. Such a product is commonly referred to as structural insulated sheathing (SIS). A SIS product provides a combination of thermal insulation, water and air barrier properties and structural strength to the light-framed wall structure of the present invention. An example of a particularly desirable exterior sheathing that provides a combination of structural integrity, barrier properties and thermal insulation in a single sheathing material is STYROFOAM SIS™ Brand Structural Insulating Sheathing (STYROFOAM SIS is a trademark of The Dow Chemical Company). ZIP insulated system sheathing is also suitable (available from Huber Engineered Woods LLC) that provides structural integrity, barrier properties and thermal insulation together in a single sheathing material.
Use of thermally insulating exterior sheathing, such as SIS or insulating foam panels, in the present invention results in a thermally insulating layer that completely covers studs by overlaying the exterior surface of the wall frame. As a result, the thermally insulating exterior sheathing precludes the studs from efficiently acting as thermal shorts through the light-framed wall structure. Reducing, even eliminating studs from acting as thermal shorts through a wall provides a superior thermally insulated wall structure over more common light-framed wall structures containing thermal insulation only in stud cavities.
The sheathing is attached to a surface of the wall frame by any means now known or yet to be discovered in the building industry. Examples of suitable means include any one or any combination of more than one of the following: mechanical fasteners (such as screws, pins, nails and staples), liquid adhesives (such as caulks and glues), and foam adhesives (such as thermoset foams including polyurethane spray foam), and plasticized adhesives (such as hot-melt glue). It is desirable to use an adhesive to adhere the sheathing to the wall frame, either alone or in combination with mechanical fasteners, with a continuous bead of adhesive along the wall frame members. Maximizing the surface of the wall frame to which the sheathing attaches maximizes the mechanical strength of the resulting light-frame wall structure.
The stud cavity of the light-framed wall structure desirably contains polyurethane foam around the inside perimeter of a stud cavity and affixed to the studs, top plate, bottom plate and sheathing (that is, affixed simultaneously to each of these wall structural elements). The polyurethane foam adjoins the building elements together around the inside perimeter of the stud cavity, joining the sheathing to the studs, top plate and bottom plate much like a fillet weld. The polyurethane foam desirably extends a distance of at least 1.5-inches over the studs, top plate, bottom plate and sheathing around the inside of the perimeter of the stud cavity to ensure a good seal and strong structural reinforcement of the wall structure. For optimal sealing performance and structural integrity the polyurethane foam should be continuous around the inside perimeter of the stud cavity. However, occasional breaks or spaces in the foam around the perimeter can be acceptable.
The polyurethane foam desirably has a greater expanded thickness proximate to the top plate than on average within a stud cavity. Polyurethane foam proximate to the top plate can support and stabilize the top plate from bending and twisting under load. Stabilization of the top plate is achievable without requiring the same thickness of polyurethane foam throughout the stud cavity. Therefore, a cost effective way to stabilize the top plate is to dispose polyurethane foam to a thicker expanded thickness proximate to the top plate. The polyurethane foam is present at an average thickness of 3.5-inches within the volume of the stud cavity within six inches, preferably within eight inches, more preferably within ten inches of the top plate. Measure polyurethane foam thickness perpendicular to the sheathing to which it is affixed.
To further increase thermal insulating properties of the wall it is desirable that the spray polyurethane foam has an average expanded thickness of at least 0.5 inches within the stud cavity and desirably has an expanded thickness of at least one inch, preferably at least 1.5 inches and more preferably at least two inches within the stud cavity. Measure the expanded thickness of the polyurethane foam perpendicular to the sheathing to which the polyurethane is affixed. The polyurethane foam provides thermal insulation to the light-framed wall structure as well as additional structural reinforcement. By binding to the wall structural elements the polyurethane foam reinforces those elements from moving with respect to one another and, as such, provides strength to the light-framed wall structure. Desirably, the polyurethane foam extends throughout the stud cavity and covers sheathing on at least one surface of the wall frame that would otherwise be exposed within the stud cavity in order to provide thermal insulation, air and vapor barrier properties and structural reinforcement throughout the entire stud cavity.
Polyurethane foam can, but does not necessarily, fill a stud cavity. Commonly, the thickness of the polyurethane foam is less than the width of the stud and so there is still void space within a stud cavity. Moreover, electrical fixtures and wiring, plumbing pipes and the like can exist within a stud cavity in combination with the polyurethane foam. Polyurethane foam can be introduced into stud cavities before or after installation of electrical components (fixture, wiring, and the like) and/or plumbing components. Beneficially, the polyurethane foam can expand within the stud cavity around the electrical and/or plumbing components.
The polyurethane foam is desirably a spray-in-place (or simply “spray”) polyurethane foam. Spray polyurethane foam inherently attaches to wall structural elements (studs, plates and sheathing) that it contacts as it cures. Application of spray polyurethane foam to a light-framed wall structure can occur with the light-framed wall structure in any orientation including a vertical orientation, such as is typically the orientation in a completed building structure. Spray polyurethane foam is becoming common in the construction industry as an insulating material. A desirable feature of spray polyurethane foam is that it can be applied to a wall structure on the construction site or any time prior to arriving at the construction site and to a wall structure in any orientation. Another desirable feature of spray polyurethane foam is that it can be applied at a constant or a variable thickness within a stud cavity. For example, the polyurethane foam can be applied thicker proximate to the top plate than on average within a stud cavity in order to provide greater structural integrity proximate to the top plate. Spray polyurethane foam can be readily applied thicker proximate to the top plate in order to achieve such a configuration. Measure polyurethane foam thickness perpendicular to the sheathing material to which it is affixed.
Other than spray-in-place polyurethane foams, pour-in-place polyurethane foams are also suitable, particularly for prefabricated light-framed wall structures that are made remotely from the construction site and delivered as a unitary structure to the construction site. As with spray polyurethane foams, pour-in-place polyurethane foams inherently tend to adhere to the building elements they contact as they cure.
The polyurethane can have an open cell or closed cell structure, though closed cell foam is generally preferred because it is often a better thermal insulator and mechanically stronger foam. Closed cell foam has an open cell content of 30% or less, preferably 20% or less, more preferably 10% or less, still more preferably 5% or less and most preferably 1% or less according to ASTM method D-6226.
The polyurethane foam desirably has a density of 0.4 pounds per cubic foot (pcf) or more, preferably 0.5 pcf or more or more and can be one pcf or more. At the same time, the polyurethane foam desirably has an expanded density of 2.8 pcf or less, preferably 2.2 pcf or less and can be 2.0 pcf of less. When the polyurethane foam has an expanded density below 0.4 pcf it provides less than optimal structural reinforcement to the light-framed wall structure. When the polyurethane foam expanded density exceeds 2.8 pcf a higher cost and reduction in thermal insulation of the foam tends to outweigh an enhanced mechanical strength. Generally, open cell polyurethane foam is lower density foam than closed cell foam. Open celled foam is commonly available as nominally 0.5 pcf foam and closed cell foam is commonly available as nominally two pcf foam.
Characteristic of the present invention is use of a single top plate in combination with a stud spacing in a range that is nominally 16-24 inches on center. Yet the light-framed wall structure of the present invention surprisingly has the further characteristics of concomitant unexpectedly high axial point, lateral and transverse load bearing properties. Light-framed wall structures of the present invention surprisingly can concomitantly support: (1) axial point loads of 2500 pounds or more, even 3000 pounds or more according to ASTM method E72, Section 9 as modified in the Example below (exclusion of the I-beam along the top plate); (2) lateral loads of 500 pounds per linear foot (plf) or more, even 750 plf or more, and even 1000 plf or more according to ASTM method E72, Section 14; and (3) transverse loads of 150 pounds per square foot (psf) or more, even 200 psf or more, and even 250 psf or more according to ASTM method E72, Section 11.
Even with a single top plate and stud spacing of a nominal 24 inches on center, and even when using 2×4 studs with a single top plate and stud spacing of a nominal 24 inches on center, wall structures of the present invention can achieve these demanding axial point load bearing values without having to position the axial point load within one inch of a stud, as the building codes presently specify. Such an achievement is a valuable advancement in the art by achieving prescribed structural integrity while reducing the framing factor of a structure. Reducing the framing factor corresponds to reducing the amount of a structure's surface area that corresponds to framing (for example, studs, top plates, and bottom plates). The framing can serve as thermal shorts through the walls of a building so reducing the framing factor of a structure allows for reduced thermal shorts through the wall of the structure.
These surprising load bearing characteristics make the light-framed wall structure of the present invention exceptionally desirable in the building industry because the light-framed wall structure offers desirably high mechanical integrity with versatility in placing loads relative to stud positions all while reducing the number of framing elements relative to common light-framed wall structure designs. For example, 2×4 studs with a nominal 24 inch spacing and with a single top plate can be used without requiring roof rafters or floor joints to align within one inch of the studs of the present invention. Moreover, use of thermally insulating exterior sheathing provides efficient thermally insulating properties and reduces or minimizes thermal shorts through the light-framed wall structure caused by studs.
Another aspect of the present invention is a process for making the light-framed wall structure of the present invention. The process comprises assembling studs nominally spaced 24 inches on center between a single top plate and a bottom plate so as to form a wall frame that defines stud cavities between the studs and the top and bottom plates and affixing the studs to the top and bottom plates; affixing a sheathing onto a surface of the wall from over the studs and stud cavities; and disposing a polyurethane foam into the stud cavity onto the exterior sheathing and against the studs and top and bottom plates so as to have an average expanded thickness of at least two inches within the stud cavity and so that the polyurethane foam attaches to the sheathing, studs and top and bottom plates of the stud cavity. The process can include applying and affixing sheathing to both the exterior and the interior surfaces of the wall frame. Each of the building elements and various embodiments of the elements and structures for use in the process of the present invention are as described for the wall structure of the present invention.
Yet another aspect of the present invention is a building structure comprising the light-framed wall structure of the present invention. The light-framed wall structure of the present invention has utility as a wall for a building structure. A building structure comprising the light-framed wall structure of the present invention is not possible apart from the light-framed wall structure of the present invention. Therefore, the building structure comprising the light-framed wall structure of the present invention is yet another embodiment of the present invention.
The following Example serves to illustrate an embodiment of the present invention. Notably, transverse load values were not actually measured but are expected to exceed 200 psf based on prior testing of similar structures with fewer components.

EXAMPLE 1

Absent Interior Sheathing

FIG. 1 illustrates two different views of light-framed wall structure 10 of the present invention and Example in order to further facilitate understanding of the present invention.
Position two 2×4 dimensional lumber studs 20 that are 93 inches long between single 2×4 dimensional lumber top plate 30 and single 2×4 dimensional lumber bottom plate 40 and spaced apart a nominal 24 inches on center. The 2×4 dimension lumber is 1.5 inches thick and 3.5 inches wide. Fasten studs 20 to the both top plate 30 and bottom plate 40 by using two 3.5 inch long 0.162 inch diameter nails per stud to form an wall frame defining a stud cavity with one 3.5 inch wide surface from each of studs 20 and plates 30 and 40 facing the cavity. Attach to the wall frame exterior sheathing 50, a sheet of 0.5-inch thick STYROFOAM SIS™ Brand Structural Insulated Sheathing, so as to cover the stud cavity from one side of the wall frame. Attach sheathing 50 to the wall frame using 7/16-inch crown by two-inch long 16 gauge staples.
Spray polyurethane foam 60 (for example, Dow Spray Foam 2045, available from The Dow Chemical Company) into the stud cavity to an expanded thickness of at least two inches. Over the area within 6 inches of top plate 30 spray polyurethane foam 60 to an expanded thickness of 3.5 inches. Cover any of sheathing 50 otherwise exposed in the stud cavity with spray foam 60 and dispose spray foam 60 against studs 20 and plates 30 and 40 around the perimeter of the stud cavity. Spray foam 60 expands to an average density of 2.2 pcf.
Test the resulting light-framed wall structure 10 to a lateral load wall strength test (ASTM E72, Section 14) and a modified axial point load wall strength test (ASTM E72, Section 9). Modify the axial point load wall strength test by excluding the I-beam spanning the stud cavity over top plate 30. In other words, apply the axial point load directly onto top plate 30 centrally between studs 20. This modification makes it more difficult for light-framed wall structure 10 to support axial point loads because the I-beam is not present to help distribute the load. Nonetheless, light-framed wall structure 10 performs remarkably well in each of the lateral load wall strength test, transverse load test and the modified axial point load wall strength test.
The Example light-framed wall structure 10 withstands lateral loads up to 1081 plf. For reference, a comparative code compliant light-framed wall structure with 2×4 studs 16 inches on center and using a double top plate with fiberglass insulation in the stud cavity and wood structural panel sheathing fasten with 0.113 shank diameter nails and 6 inches on center at the edges and 12 inches on center on non-edge studs, and covering the exterior surface of the wall frame only bears up to 515 plf in the lateral load test.
The Example wall structure 10 withstands axial point load up to 3294 pounds in the modified axial point load wall strength test.
This Example illustrates a light-framed wall structure of the present invention that can support remarkably high lateral, axial point and transverse loads despite having a single top plate and 2×4 studs positioned a nominal 24 inches on center.
The performance of wall structure 10 would only improve (that is, load values would stay the same or increase) with the inclusion of interior sheathing. Hence, the surprising result of the strength of this wall is independent of the type of interior sheathing that one might include to bring this example within scope of the present invention.

EXAMPLE 2

One-Inch SIS Exterior Sheathing

Prepare a wall structure similar to wall structure 10 of Example 1 except use a one-inch thick SIS panel for the exterior sheathing 50 and a spray polyurethane foam to a thickness of at least one-and-one half inches in the stud cavity while having an expanded thickness of 3.5 inches entirely within ten inches (which inherently includes the first six inches) of top plate 30. Attach an interior sheathing to the wall frame on an opposite side to the SIS exterior sheathing so as to cover the stud cavity from the inside of the wall frame. Use as interior sheathing 0.5-inch thick gypsum wall board using number 6 screws every sixteen inches around the perimeter and interior of the board.
Test the resulting light-framed wall structure in like manner as the first example except use unrestrained ASTM E-2126 for testing lateral load wall strength. The “unrestrained” test format means that the wall is only anchored to a test base with ½-inch anchor bolts every six feet and not restrained with other hold-downs or tie down rods. The resulting wall structure has a capacity of 759 pounds per lineal foot under the lateral load test and 4031 pounds in the axial load wall test.

EXAMPLE 3

Wood Exterior Sheathing

Prepare a wall structure similar to wall structure 10 in Example 1 except use as the exterior sheathing 7/16-inch thick grade PS2 24/0 oriented strand board. Test the resulting light-framed wall structure in like manner as wall structure 10 in Example 1.
The resulting wall structure has a capacity of 1422 pounds per lineal foot under the lateral load test; an excess of 200 psf in the transverse load test and 7348 pounds in the axial load wall test. As with Example 1, addition of interior sheathing would not diminish these values and so including any interior sheathing to the structure of this example would have at least these surprisingly high capacity values.

EXAMPLE 4

Gypsum Board Sheathing

Prepare a wall structure similar to wall structure 10 in Example 1 except use as the sheathing ½-inch thick standard interior gypsum board. Test the resulting light-framed wall structure in like manner as the wall structure in Example 2.
The resulting wall structure has a capacity of 678 pounds per lineal foot under the lateral load test and 4262 pounds in the axial load wall test. Test results are expected to stay the same or increase if another sheathing was included on an opposing side of the wall structure.

EXAMPLE 5

Extruded Polystyrene Foam Sheathing

Prepare a wall structure similar to wall structure in Example 2 except use as the exterior sheathing one-inch thick extruded polystyrene foam (STYROFOAM™ Residential Sheathing, STYROFOAM is a trademark of The Dow Chemical Company). Test the resulting wall structure in like manner as the wall structure in Example 2.
The resulting wall structure has a capacity of 490 pounds per lineal foot under the lateral load test; an excess of 200 psf in the transverse load test and 3494 pounds in the axial load wall test.

EXAMPLE 6

Structure with Polyurethane Fillet Picture Framing

Prepare a wall structure similar to the wall structure in Example 2 except deposit the spray polyurethane foam as a triangular shaped bead around the inside perimeter of the stud cavity and in the top ten inches (as measured from the top plate) of the stud cavity. The spray polyurethane triangular cross section bead measures 1.5 inches by 1.5 inches at the legs of the triangle, with one leg extending over the sheathing and the other leg extending over a stud, top plate or bottom plate. The volume of the stud cavity within ten inches of the top plate is filled to an expanded depth of 3.5 inches of polyurethane foam.
FIG. 2 illustrates a view of the Example 7 wall structure without the interior sheathing and viewing from the interior side of the wall structure. Wall structure 10 comprises 2×4 dimensional lumber studs 20 that are 93 inches long between single 2×4 dimensional lumber top plate 30 and single 2×4 dimensional lumber bottom plate 40 and spaced apart a nominal 24 inches on center. The 2×4 dimensional lumber is 1.5 inches thick and 3.5 inches wide. Exterior sheathing 50 is a sheet of one-inch thick STYROFOAM SIS™ Brand Structural Insulated Sheathing. Spray polyurethane foam 60 extends around the interior perimeter of the cavity and fills the top ten inches within the cavity.
Test the wall structure in like manner as Example 2. The resulting wall structure has a capacity of 699 pounds per lineal foot under the lateral load test, and (though not tested) is expected to achieve at least 4031 pounds in the axial load wall test due to the similarity of the structure to that in Example 2.

Claims

1. A light-framed wall structure comprising:

(a) studs spaced apart from one another in a range of nominally 16 to nominally 24 inches on center;

(b) a bottom plate and a single top plate spanning the studs and attached to opposing ends of the studs such that the studs, top plate and bottom plate define a wall frame having opposing interior and exterior surfaces with the studs, top and bottom plate further defining a stud cavity within the wall frame, the stud cavity having a height extending from bottom plate to top plate and a width extending from one stud to another stud;

(c) sheathing spanning the width and height of the stud cavity and overlapping the studs and attached to at least one of the exterior and interior surfaces of the wall frame; and

(d) polyurethane foam forming a seal around the inside perimeter of the stud cavity and affixed to the sheathing material on at least one surface of the wall frame, the stud, top plate and bottom plate where the polyurethane foam extends at least 1.5 inches over the sheathing, studs, top plate and bottom plate along the perimeter and further is present at an average thickness of at least 3.5 inches over the volume of the stud cavity within six inches of the top plate;

wherein the light-framed wall structure is free of metal corner connectors or reinforcements comprising a box-shaped section against which the studs, bottom plate and top plate abut.

2. The light-framed wall structure of claim 1, wherein the studs are 2×4 dimensional building elements spaced apart from one another a nominal 24 inches on center.

3. The light-framed wall structure of claim 1, wherein the sheathing material is selected from structural insulated sheathing, rigid insulated sheathing and gypsum board.

4. The light-framed wall structure of claim 1, wherein the sheathing material is structural insulated sheathing.

5. The light-framed wall structure of claim 1, wherein the polyurethane foam entirely covers any sheathing attached to at least one of the interior and exterior surfaces of the wall frame that would otherwise be exposed within the stud cavity.

6. The light-framed wall structure of claim 1, wherein the polyurethane foam has a thickness anywhere in the stud cavity of at least one and one half inches thick as measured perpendicularly from the sheathing material to which the polyurethane foam is affixed.

7. The light-framed wall structure of claim 1, wherein the sheathing is exterior sheathing attached to the exterior surface of the wall frame.

8. The light-framed wall structure of claim 7, further comprising interior sheathing spanning the width and height of the stud cavity and overlapping the studs and attached to the interior surface of the wall frame.

9. A light-framed wall structure comprising:

(a) studs nominally spaced apart from one another 24 inches on center;

(c) exterior sheathing spanning the width and height of the stud cavity and overlapping the studs and attached to the exterior surface of the wall frame; and

(d) polyurethane foam within the stud cavity and affixed to the exterior sheathing material, studs, top plate and bottom plate defining the stud cavity, the polyurethane foam having an average thickness of at least 0.5 inches within the stud cavity;

10. A process for making the light-framed wall structure of claim 1, the process comprising the following steps:

(a) assembling studs spaced apart from one another in a range of nominally 16 to nominally 24 inches on center between a single top plate and a bottom plate so as to form a wall frame having opposing interior and exterior surfaces and defining a stud cavity between the studs and top and bottom plates and affixing the studs to the top and bottom plates;

(b) affixing sheathing to at least one of the exterior and interior surfaces of the wall frame over the studs and stud cavity; and

(c) disposing a polyurethane foam into the stud cavity so as to form a seal around the inside perimeter of the stud cavity that is affixed to the sheathing material on at least one surface of the wall frame, the studs, top plate and bottom plate defining the stud cavity, the polyurethane foam being disposed in such an amount so as to have an average thickness of at least 3.5 inches in the stud cavity within six inches of the top plate and extending at least 1.5 inches over the studs, top plate, bottom plate and sheathing around the inside perimeter of the stud cavity;

wherein the light-framed wall structure is free of metal corner connectors or reinforcement comprising a box-shaped section against which the studs, bottom plate and top plate abut.

11. The process of claim 10, wherein the studs are 2×4 dimensional building elements and they are assembled spaced apart from one another nominally 24 inches on center.

12. The process of claim 10, wherein the sheathing is selected from structural insulated sheathing material, rigid insulated sheathing and gypsum board.

13. The process of claim 10, wherein the polyurethane foam is a spray polyurethane foam and step (c) includes spraying the polyurethane foam into place.

14. The process of claim 10, wherein polyurethane foam is disposed so as to entirely cover any sheathing attached to at least one of the interior and exterior surfaces of the wall frame that would otherwise be exposed within the stud cavity.

15. The process of claim 10, wherein the polyurethane foam is disposed so as to have an average expanded thickness of at least 1.5 inches within the stud cavity as measured perpendicularly from the sheathing to which the polyurethane foam is affixed.

16. The process of claim 10, wherein the polyurethane foam is disposed to a greater thickness proximate to the top plate than on average within the stud cavity.

17. The process of claim 10, comprises affixing sheathing to both the exterior and the interior surfaces of the wall frame over the studs and stud cavities.

18. The process of claim 10, wherein the wall frame has multiple stud cavities defined therein by the studs, top plate and bottom plate and wherein step (b) includes affixing sheathing over multiple stud cavities and step (c) includes disposing polyurethane as described into multiple stud cavities.

19. A building structure comprising the light-framed wall structure of claim 1.