Abstract:
A bracket apparatus for an insulated building structure includes: a sheathing mounting element including a mounting surface configured to receive a mechanical fastener; and at least one elongated spacer extending away from the sheathing mounting element by a predetermined stand-off distance, the spacer configured to penetrate fibrous insulation, and defining a contact pattern configured to prevent pivoting motion of the spacer relative to a planar surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Provisional Application No. 61/296,256, filed Jan. 19, 2010. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to building structures and more particularly to apparatus for accommodating the installation of thermal insulation in such buildings. 
     One well-known type of building structure is a so-called “metal building” in which a series of spaced-apart structural steel frames are erected on a foundation and then covered with metallic sheathing. 
     In general it is considered desirable to include as much thermal insulation as possible in all types of buildings to minimize heat gain and loss, and consequently minimize energy expenditures for heating and cooling. Furthermore, in recent times government building codes have come to require much more insulation in wall and roof structures than in the past. 
     The roof and wall structures of conventionally-constructed metal buildings are not well adapted to the installation of large amounts of insulation. In particular, the structure and methods used to install roof sheathing crush the insulation to a small thickness at the sheathing mounting points, seriously degrading the insulation&#39;s performance. 
     Methods are available to prevent crushing the insulation in a metal building. They typically involve the installation of a grid or net of straps underneath an existing roof structure, which is then used to support the insulation. Unfortunately, these methods require a great deal of labor and materials, and result in high costs. 
     BRIEF SUMMARY OF THE INVENTION 
     These and other shortcomings of the prior art are addressed by the present invention, which provides a structure suitable for installing insulation without crushing. 
     According to one aspect of the invention, a bracket apparatus includes: a sheathing mounting element including a mounting surface configured to receive a mechanical fastener; and at least one elongated spacer extending away from the sheathing mounting element by a predetermined stand-off distance, the spacer configured to penetrate fibrous insulation, and defining a contact pattern configured to prevent pivoting motion of the spacer relative to a planar surface. 
     According to another aspect of the invention, an insulated building structure includes: an array of spaced-apart elongated structural members; an array of spaced-apart elongated intermediate members interconnecting the spaced-apart structural members; a layer of thermal insulation lying across the array of intermediate members; a plurality of spacers positioned in contact with the intermediate members, each spacer penetrating the thermal insulation and extending away from the associated intermediate member by a predetermined stand-off distance; and a plurality of sheathing mounting elements positioned in contact with the spacers, each sheathing mounting element including a mounting surface exposed outside the thermal insulation that is configured to receive a mechanical fastener. 
     According to another aspect of the invention, a method is provided for insulating a building structure having an array of spaced-apart elongated structural members and an array of spaced-apart elongated intermediate members interconnecting the spaced-apart structural members, and a layer of thermal insulation lying across the array of intermediate members. The method includes: positioning a plurality of spacers in contact with the intermediate members, each spacer penetrating the thermal insulation and extending away from the associated intermediate member by a predetermined stand-off distance; and positioning a plurality of sheathing mounting elements in contact with the spacers, each sheathing mounting element including a mounting surface exposed outside the thermal insulation that is configured to receive a mechanical fastener. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
         FIG. 1  is a cross-sectional view of a portion of the structure of a prior art building; 
         FIG. 2  is a cross-sectional view of a portion of the structure of a building constructed according to an aspect of the present invention; 
         FIGS. 3 ,  4 , and  5  are top, side, and cross-sectional views, respectively, of a bracket constructed according to an aspect of the present invention; 
         FIGS. 6 and 7  are top and side views, respectively, of an alternative bracket constructed according to an aspect of the present invention; 
         FIGS. 8 ,  9 , and  10  are top, side, and cross-sectional views, respectively, of another alternative bracket constructed according to an aspect of the present invention; 
         FIG. 11  is a cross-sectional view of a portion of a building structure, showing details of attachment of a bracket thereto; and 
         FIG. 12  is a cross-sectional view of a portion of a building structure, showing the installation of supplemental insulation. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIG. 1  depicts a portion of the structure of a building  10 , which is constructed in a known manner on top of a concrete slab  12  or other suitable foundation. The building is of a type generally referred to in the construction industry simply as a “metal building”. Structural support for the building is provided by a series of spaced-apart frames  14 . Each of the frames  14  is generally an inverted “U” shape and is built up from spaced-apart posts  16  interconnected by rafters  18 . In a typical building of this type, the posts  16  and rafters  18  are steel I-beam elements which are fastened together using suitable brackets and fasteners (e.g. bolts or rivets). The term “structural member” may be used herein to refer generically to both the posts  16  and rafters  18 . 
     A series of elongated, horizontally-oriented members are attached to the outer surfaces of the frames  14  at regular intervals. These members serve as a rigid intermediate structure to which the outer sheathing of the building is attached. In common construction parlance the members attached to the posts  16  are referred to as “girts”  20 , and the members attached to the rafters  18  are referred to as “purlins”  22 . The term “intermediate member” may be used herein to refer generically to both the girts  20  and purlins  22 . 
     In the illustrated example, each of the girts  20  and the purlins  22  is a member formed from sheet metal having a generally “Z”-shaped cross-section. Other sectional shapes, such as “C” and “hat” are known as well. The girts  20  and purlins  22  would typically be attached to the posts  16  and rafters  18  using mechanical fasteners such as bolts and nuts. 
     Insulation  24  is laid over the purlins  22 . A frequently-used type of insulation comprises a thick mat of glass fibers (e.g. “fiberglass”) in the form of a blanket, roll or batt. As an example, in its free state the insulation  24  would typically be about 10 cm (4 in.) to about 20 cm (8 in.) thick with a corresponding thermal resistance or “R-value” of about 12 to 25. Typically the underside of the insulation  24  would include a paper facing and/or vapor barrier material. 
     Roof sheathing  26  and siding  28  is secured to the purlins  22  and the girts  20 , respectively. The sheathing  26  and siding  28  are pressed sheet metal shapes, and are often attached using self-drilling screws  30  of a known type. The insulation  24  is crushed or compressed to a very small thickness, for example less than about 1.3 cm (½ in.) at the attachment points over the purlins  22 . This crushing greatly reduces the R-value of the insulation  24  not only at the points of minimum thickness, but also in the transition regions “T” on either side of each purlin  22 . When large areas of insulation  24  are installed over many purlins  22 , the total degradation in insulation performance can be significant. 
       FIG. 2  illustrates a portion of the structure of a building  110  which is constructed in accordance with the principles of the present invention. The building  110  is generally similar in construction to the building  10 , and includes posts  116 , rafters  118 , girts  120 , purlins  122 , insulation  124 , sheathing  126 , and siding  128 . The building  110  differs in the manner in which the insulation  124  is installed. In particular, brackets  132  of a unique configuration are attached to the purlins  122  through the insulation  124 , and the roof sheathing  126  is attached in turn to the brackets  132 . 
       FIGS. 3-5  show a short section of one of the brackets  132  in more detail. It will be understood that the bracket  132  could be produced in any length determined to be convenient and economical. The basic components of the bracket  132  are a sheathing mounting element and one or more spacers. As will be understood from examination of the examples described further below, the specific mechanical configuration of the bracket  132  is not critical so long as the bracket  132  provides an element with a small surface area for holding the sheathing  126  at a stand-off distance from the purlins  122 , and some means for accepting fasteners to secure the sheathing  126 . In the specific example shown in  FIGS. 3-5 , the mounting element is an elongated sheet metal channel  134  having an inverted “U”-shape with a web and downturned flanges. The spacers  136  take the form of sheet-metal plates which extend downward from the inner surface of the channel  134 . The spacers  136  may take any convenient shape and may be attached to the channel  134 , for example by welding or brazing, by adhesive, or by mechanical fasteners such as rivets or screws, or by a mechanical joint such as a crimp. The lateral extension of the spacers  136  across the channel  134  provides a contact pattern which is “self-balancing” or configured to prevent pivoting motion of the bracket  132  relative to the associated intermediate member (or other planar surface) when installed. 
     The channel  134  includes a number of recesses  138  which surround fastener holes  140  formed through the web. The purpose of the recesses  138  is to receive the heads of fasteners such self-drilling screws, so as to provide a flat top surface when the sheathing  126  is installed. The recesses  138  are believed to make installation of sheathing  126  over the channel  134  easier, but are strictly optional. The fastener holes  140  (and their associated recesses  138 ) may be offset relative to the centerline of the channel  134  in order to provide a more stable mounting, as well as to reduce the chance that a fastener will be struck when sheathing  126  is attached to the channel  134 . An example of a suitable distance between the fastener holes  140  along the length of the bracket  132  is about 30.5 cm (12 in.). 
     To accommodate fasteners, the portions of the spacers  136  which would otherwise be aligned with the fastener holes  140  have shallow grooves  142  formed therein, for example by stamping. Fasteners could also be accommodated by using tubes or hollow construction for the spacers  136 , or by offsetting the spacers  136  so they are not aligned with the fastener holes  140 . The spacers  136  could also be made in two separate pieces, with one piece being placed on each side of the fastener hole  140 . 
     The specific materials for the components of the bracket  132  may be varied to suit a particular application in terms of thickness, dimensions, material selection, and coatings. One particular material known to be suitable for this application is sheet steel coated with 55% aluminum-zinc alloy and sold commercially as GALVALUME, which is available from BIEC International, Inc., Vancouver, Wash. 98660 USA. In the specific example discussed, the thickness of the bracket components is in the range of about 1.2 mm (0.048 in. or 18 gage) to about 1.9 mm (0.075 in. or 14 gage). 
       FIGS. 6 and 7  illustrate an alternative bracket  232  which includes a channel  234  and a single continuous sheet metal spacer  236  having a saw-tooth shape. The spacer  236  may be attached to the channel  234 , for example by welding or brazing, by adhesive, or by mechanical fasteners such as rivets or screws, or by a mechanical joint such as a crimp. The lateral extension of the spacer  236  provides a contact pattern which is “self-balancing” or configured to prevent pivoting motion of the spacer  236  relative to the associated intermediate member (or other planar surface) when installed. Therefore, alternatively, it may be provided as a separate element from the channel  234 . 
       FIGS. 8 ,  9 , and  10  illustrate yet another alternative bracket  332  which includes a channel  334  and a plurality of tubular spacers  336 . The channel  334  includes a number of recesses  338  which surround fastener holes  340 . The spacers  336  are secured to the bottom surfaces of the recesses  338  in alignment with the fastener holes  340 , and may be attached, for example, by welding or brazing, by adhesive, or by mechanical fasteners such as rivets or screws, or by a mechanical joint such as a crimp. The lateral spacing of the spacers  336  across the channel  334  provides a contact pattern which is “self-balancing” or configured to prevent pivoting motion of the bracket  332  relative to the associated intermediate member (or other planar surface) when installed. 
     Using the bracket  132  described above as an example, and referring to  FIG. 2 , insulation  124  may be installed as follows. Once the frames and purlins  122  are installed, the insulation  124  may be laid over the purlins  122  as in conventional practice. Then, the brackets  132  are installed to the purlins  122  by pushing the brackets  132  through the insulation  124 . The spacers  136  have a very small surface area and consequently may be expected to “cut” or “stab” (or otherwise penetrate) through the insulation  124  in order to contact the underlying purlins  122  without crushing the insulation  124 .  FIG. 11  depicts a small section of the structure with the insulation removed so that the relationship of the bracket  132  and purlin  122  is visible. Once the bracket  132  is laid in place, it is secured with appropriate fasteners, such as self-drilling screws  129 , passing through the fastener holes  140  and into the purlins  122 . The sheathing  126  may then be attached to the brackets  132 , again with conventional fasteners such as self-drilling screws  130 . 
     When completed, the brackets  132  provide a definite stand-off distance between the sheathing  126  and the purlins  122 , in effect guaranteeing that a minimum effective amount of insulation  124  will be present across the entire surface area of the roof. In the illustrated example the stand-off distance is about 7.6 cm (3 in.) to about 12.7 cm (5 in.), but this distance may be varied over a wide range to suit a particular application or building code requirement. Because the spacers  136  have a very small surface area for their length, they contribute only a minimum amount of heat transfer between the sheathing  126  and the purlins  122 . As an illustration of this property, it is noted that the length-to-thickness ratio of the exemplary spacers  136 , using the example dimensions described above, and measured parallel to the stand-off distance, is about 40 or more. 
     To further enhance the effectiveness of the insulation  124 , and mediate any heat transfer effect of the brackets  132 , supplemental insulation may be provided.  FIG. 12  depicts a strip of supplemental insulation  141  which is laid over the bracket  132 . Its major dimension is parallel to the purlin  122  and it extends laterally across the portion of the insulation  124  which is compressed by the bracket  132 . In the illustrated example, the supplemental insulation  141  is about 6.4 mm (¼ in.) thick before installation, and approximately 20 cm (8 in.) wide, measured parallel to the rafter  118 . The outer surface of the supplemental insulation  141  is faced with foil to reduce radiant heat losses, and the inner surface of the supplemental insulation  141  is faced with plastic to act as a vapor barrier. During installation, the sheathing  126  is placed over the supplemental insulation  141  and then the fasteners (e.g. self-tapping screws  130 ) are driven through the sheathing  126 , the supplemental insulation  141 , and the brackets  132 . 
     It should be noted that the construction technique described for the roof of the building  110  may be applied with equal effectiveness to the wall structure. As seen in  FIG. 2 , brackets  132  may be attached to the girts  120  and additional insulation may be applied between the girts  120  and the siding  128 . This is in stark contrast to conventional practice, which would require the construction of a secondary wall structure inside the building in order to support wall insulation. 
     The structure described above provides numerous advantages over prior art “metal building” construction. In particular, it allows the installation of insulation so that it will be effective with low labor and materials costs. 
     The foregoing has described an insulated building structure. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation.