A method of facing a roof structure includes securing a facing to respective lower flanges of first and second spaced-apart purlins of the roof structure, with the facing extending directly between the respective lower flanges of the first and second purlins. A carriage is suspended from purlins of the roof structure and supports a roll of facing. The facing is dispensed and adhesively secured to the purlins by moving the carriage relative to the purlins and/or by maintaining the carriage in a stationary position and pulling facing from the roll of facing supported on the carriage. The resulting faced roof structure provides an enhanced appearance and more uniform and higher R-value insulation.

CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from and benefit of the filing date of U.S. provisional patent application Ser. No. 61/121,165 filed Dec. 9, 2008, and the full disclosure of said provisional application is hereby expressly incorporated by reference into the present application. 
    
    
     BACKGROUND 
       FIG. 1  illustrates a known (prior art) building roof structure R comprising a corrugated metal or other roof deck D supported on plurality of parallel, spaced-apart purlins, trusses or other structural members P that extend axially along respective longitudinal axes PX that each extend perpendicularly into and out of the page as shown in  FIG. 1 . Between each successive pair of purlins P, an open bay BA is defined, and the roof deck D spans the bays BA. It is known to insulate the roof deck D with a known roof insulation system  10 . Typically, as shown in  FIG. 1 , the known roof insulation system  10  comprises a vapor retarder facing or web or sheet S draped over the respective upper flanges or edges PU of multiple (at least two) successive purlins P so that the sheet S spans and drapes across one or more bays BA. The vapor retarder sheet S is fixed to at least some or all of the purlins P over which it is draped using suitable fasteners, adhesive or other means. The vapor retarder sheet S is a single layer or multiple layer product, e.g., single-layer vinyl film/sheet or other film/sheet, or a laminated composite containing various combinations of aluminum foil, polymeric film/sheet, kraft paper, reinforcing yarns and/or fabrics. Vapor retarder sheets S vary in strength, color, light reflectivity, and their ability to retard moisture migration therethrough. An insulation space SP is thus defined between the inner face S 1  of the sheet S and the roof deck D, and fiber glass or other insulation I is laid or blown or otherwise installed in the insulation space SP and is supported on the inner face S 1  of the vapor retarder sheet S and/or laminated to the inner face S 1  vapor retarder sheet S. The vapor retarder sheet S supports and faces the insulation I, inhibits migration of moisture into the insulation and improves aesthetics of the interior of the building. 
     The roof insulation system  10  of  FIG. 1  has been found to be suboptimal in certain cases. For example, the draped vapor retarder sheet S limits the amount of insulation that can be installed in the bay BA, and the insulation is uneven between the central portion of the bay and the edges adjacent the purlins P. The sheet S can be stretched too taught across the bay BA, which shortens the insulation space SP. As such, the R-value achievable with the system  10  of  FIG. 1  can sometimes be limited and/or inconsistent. Also, some people find the draped facing sheet S to lack the desired aesthetics for a roof structure due to the exposed purlins and uneven appearance. 
     SUMMARY 
     In accordance with one aspect of the present development, a method of facing a roof structure includes securing a facing to respective lower flanges of first and second spaced-apart purlins of the roof structure, with the facing extending directly between the respective lower flanges of the first and second purlins. 
     In accordance with another aspect of the present development, a roof structure includes first and second purlins each comprising a lower flange. Facing extends directly between the respective lower flanges of the first and second purlins. 
     In accordance with another aspect of the present development, a carriage for dispensing facing for a roof structure includes a base adapted to support an associated roll of facing. First and second feet are connected to the base and are adapted to movably engage first and second associated purlins for suspending the base beneath the first and second associated purlins. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  (prior art) illustrates a known roof structure and known insulation system; 
         FIG. 2  is an isometric view of the roof structure of  FIG. 1  (or the like) and showing one embodiment of a carriage used to implement a facing system and method in accordance with the present development; 
         FIG. 2A  shows one example of an associated roll of facing to be dispensed from the carriage of  FIG. 2 ; 
         FIG. 2B  shows a roof structure including facing installed according to the present system and method; 
         FIG. 3  is a view taken at view line  3 - 3  of  FIG. 2  and shows the first base portion of the carriage of  FIG. 2 ; 
         FIG. 4  is a view taken at view line  4 - 4  of  FIG. 2  and shows the second base portion of the carriage of  FIG. 2 ; 
         FIG. 5  shows one example of a roll support device of the carriage of  FIG. 2  and shows the facing roll of  FIG. 2A  operably supported thereby; 
         FIG. 6  shows an alternative embodiment of a carriage in accordance with the present development; 
         FIG. 7  is an isometric view of the roof structure of  FIG. 1  (or the like) and showing another alternative embodiment of a carriage used to implement a facing system and method in accordance with the present development; 
         FIG. 8  is a side view of the carriage of  FIG. 7 , pivoted to its operative position for installing facing in accordance with the present development; 
         FIGS. 9A and 9B  are views of the carriage as taken along view line  9 - 9  of  FIG. 8 , with  FIG. 9A  showing the carriage in an extended condition for use with a first (wider) purlin spacing and  FIG. 9B  showing the carriage in a retracted condition for use with a second (shorter) purlin spacing; 
         FIG. 10  is a view of the carriage and associated roof purlins as taken along view line  10 - 10  of  FIG. 8 ; 
         FIG. 11  is a view similar to  FIG. 7 , but showing another alternative embodiment of a carriage formed in accordance with the present development. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  illustrates the known building roof structure R as generally described above, comprising a corrugated metal or other roof deck D supported on plurality of parallel, spaced-apart purlins P (only first and second purlins P 1 ,P 2  are shown in  FIG. 2 ). Between each successive pair of purlins P, an open bay BA is defined, and the roof deck D spans the bays BA. According to the present development, in order to insulate the roof structure R, a vapor retarder facing or other facing F (see  FIGS. 2B and 7 ) is secured to bottom face PF of the lower flange PL of multiple (at least two) parallel spaced-apart purlins P so that the facing F directly spans one or more bays BA, without being draped over the upper flanges PU of the purlins P. Each bay BA is then at least partially filled with fiber glass or other insulation that is supported on the facing F. As described in further detail below, the facing F is initially fixedly secured to the bottom face PF of each purlin lower flange PL using adhesive (for example, double-sided tape or other adhesive) and, preferably, is thereafter more permanently secured using screws and/or other mechanical fasteners that connect to the purlins P. The facing F, itself, comprises a single layer or multiple layer product, e.g., single-layer vinyl film/sheet or other film/sheet, or a laminated composite containing various combinations of aluminum foil, polymeric film/sheet, kraft paper, reinforcing yarns and fabrics. Facings F vary in strength, color, light reflectivity, and their ability to retard moisture migration therethrough. As noted, the facing F can inhibit migration of moisture into the insulation (if the facing F is constructed as a vapor retarder) and improves aesthetics of the interior of the building. In some applications, the facing F is perforated or otherwise constructed to allow migration of moisture therethrough. Regardless of the exact structure of the facing, the terms “sheet” or “web” as used herein are intended to refer to a length of the facing F having a width sufficient to span the bay BA so as to extend directly between the lower flanges PL of the purlins P 1 ,P 2 . 
     As shown in  FIG. 2 , according to the present development, the facing F is installed using a carriage C that is temporarily secured to/suspended from and moved along at least two of the purlins P 1 ,P 2 , parallel to the longitudinal axes PX thereof. The carriage C is adapted to carry one or more rolls RF ( FIG. 2A ) of the facing F and to dispense the facing for securement to the lower flanges PL at least two of the purlins P 1 ,P 2  by tape or other adhesive. More particularly, the carriage C is adapted to be movably secured to the lower flanges PL and ride along same in a direction D 1  parallel with the axes PX of the purlins P 1 ,P 2  and to dispense the facing F from the roll RF as it moves along the purlins. As shown in  FIG. 2A , the facing F includes double-sided tape or other first and second adhesive zones Z 1 ,Z 2  respectively located at least adjacent its opposite first and second lateral sides that adhere to the bottom face PF of the purlin lower flange PL to secure the facing F to the purlins (the adhesive zones Z 1 ,Z 2  can be separate zones or can both be part of a larger single adhesive area). Alternatively, adhesive (e.g., double-sided tape or other adhesive) can first be applied to the bottom face PF of the purlin lower flanges PL through a manual process or using the carriage C to define the first and second adhesive zones Z 1 ,Z 2 . After the facing F is dispensed from the carriage C and adhered to the purlins P, optional screws, clips and/or other mechanical fasteners can be installed using conventional methods, e.g, screws installed through the facing into the lower flange PL, for strengthening the connection between the facing F and the purlins P. Unlike known system such as that shown in  FIG. 1 , the facing F extends directly between the lower flanges PL, meaning that the facing F is not draped over the purlin upper flanges PU. The carriage C is adapted to be temporarily and movably engaged with first and second parallel spaced-apart purlins P (P 1 ,P 2 ), with a base B of the carriage C suspended beneath the purlins. As shown, the carriage C is movably engaged with successive purlins P 1 ,P 2 , but the carriage can be sized to by movably engaged with any two (or more) parallel spaced apart purlins P. In the illustrated embodiment, the carriage C is adapted to be movably engaged with the lower flanges PL of the first and second purlins P 1 ,P 2  and comprises first and second feet  12   a , 12   b  adapted to be received on an inner/upper surface of the lower flanges PL. The feet  12   a , 12   b  are adapted to slide, roll or otherwise movably engage the flanges PL for movement in a direction D 1  or opposite direction D 2  parallel to the longitudinal axes PX of the purlins, and the feet  12   a , 12   b  are preferably conformed and dimensioned to minimize movement transverse to the longitudinal axes PX. As shown, the feet  12   a , 12   b  are adapted to slide on the flanges PL, but the feet  12   a , 12   b  can include rollers, wheels or other means for moving on the flanges PL. Alternatively, the feet  12   a  can movably engage any other part of the purlins P 1 ,P 2  without departing from the overall scope and intent of the present development. 
     The base B of the carriage C comprises first and second base portions B 1 ,B 2  connected to each other by one or more cross-members XB. The cross-members are selectively adjustable in length to allow the spacing between the first and second base portions B 1 ,B 2  to be adjusted and fixed as desired so that the carriage C can be sized to engage first and second purlins P 1 ,P 2  laterally spaced from each other at various distances, such as 5 feet or more or less. The adjustable-length cross-members XB are important because purlin spacing will vary from building to building or even within the same roof structure R. In one example, the cross-members XB are telescoping poles that include a lock that allows the poles to be fixed at a desired length. The first and second base portions B 1 ,B 2  are adapted to be located generally beneath and in lateral alignment with the lower flanges PL of the first and second purlins P 1 ,P 2 , respectively. The first base portion B 1  is connected to the first foot  12   a  via one or more first struts  16   a , and the second base portion B 2  is connected to the second foot  12   b  via one or more second struts  16   b . In one embodiment, the carriage C is constructed from steel alloy or other metal components welded or otherwise connected together (e.g., metal stampings or extrusions or other structures), or can be constructed from metal wire and/or polymeric components, as a one-piece or multi-piece structure, and the illustrated structure for the carriage C is only one example not intended to limit the present development in any way. The feet  12   a , 12   b  can be defined from a durable polymeric material with a low coefficient of friction and/or can include wheels or the like. The first and second base portions B 1 ,B 2  are shown separately in  FIGS. 3 and 4 , with views taken at  3 - 3  and  4 - 4  of  FIG. 2 , respectively. As seen in  FIG. 4 , the feet  12   a , 12   b  are preferably conformed and dimensioned to fit closely between the vertical web PW of the purlin and the upturned lip FL to minimize lateral movement of the feet  12   a , 12   b  transverse to the longitudinal axis PX of the purlin P. 
     The base B includes a roll support device or other roll support means for supporting a roll RF of the facing F and for dispensing facing from the roll RF. In the illustrated embodiment of  FIGS. 2-5 , the bases B 1 ,B 2  comprise respective roll support device  20  comprising a roll support block  22  connected to a shaft  24 . The shaft  24  is slidably connected to the respective base portion B 1 ,B 2 . The roll support block  22  is adapted for vertical movement relative to its respective base B 1 ,B 2  between an extended position (closer to the purlin lower flange PL) and a retracted position (spaced farther away from the purlin lower flange PL). Means are provided for biasing each roll support block  22  to its extended position. In the illustrated embodiment, the above is accomplished connecting each shaft  24  slidably to its respective base B 1 ,B 2  and by including a coil spring  26  that is coaxially located about each shaft  24  and operatively engaged between its respective base B 1 ,B 2  and the support block  22  and/or shaft  24 . 
     As shown in  FIG. 2A , in one example, each facing roll RF can include first and second spindles  28  removably inserted in its opposite ends or otherwise projecting from its opposite ends such as, e.g., the spindles  28  being connected to or defined by the opposite ends a shaft or core that extends through the roll RF. The roll support blocks  22  each include a slot  22   s  ( FIG. 5 ) or other structure for receiving and rotatably supporting one of the spindles  28  so that the roll RF extends between the roll support blocks  22  of the bases B 1 ,B 2  and is rotatably supported for dispensing the facing F from the roll RF onto the purlin lower flange PL. The roll support devices  20  bias the roll RF upward as indicated by arrow A 1  into operative engagement with the bottom face PF of the purlin lower flanges PL such that when the carriage C is moved relative to the purlins P 1 ,P 2  in the direction D 1 , the first and second adhesive zones Z 1 ,Z 2  of the roll RF adhere the facing F to the purlin lower flanges PL as the facing F is dispensed from the roll. In an alternative embodiment, the roll RF, itself, is not biased into contact with the purlins P. Instead, one or more idler rollers or blades, or other means are used to press the facing F into contact with the purlin flanges PL after the facing is unwound from the roll RF. 
     It should be noted that adjacent bays BA of a roof structure R will be faced in a successive manner, by engaging the carriage C with each adjacent successive bay BA after facing a previous bay, i.e., after a bay BA is faced, the carriage C is moved to and engaged with the next bay BA. Also, those of ordinary skill in the art will recognize that the installed facing F of a previous bay BA will require that the bays BA be faced in a specified order/direction to allow unobstructed access to the purlin lower flanges PL for the carriage feet  12   a , 12   b  to be seated thereon (the bays BA will be faced staring with the most upstream bay and moving downstream from bay-to-bay in the direction that the flanges PL extend from the vertical web PW of the purlins P). 
     Furthermore, the facing F will typically overlap on the purlin lower flange PL and define a seam between successive adjacent bays BA. This overlapped seam is highly desired when the facing F is a vapor retarder facing and the facing is sealed by an adhesive such as tape or otherwise continuously sealed along the overlapped seam so that a continuous vapor barrier/Vapor Retarder Liner is formed by the successive overlapped strips of facing F. As used herein, the facing F is deemed to be adhered or otherwise connected to a purlin lower flange PL if the facing F is directly in contact with the purlin lower flange PL and/or if an intervening layer of tape or another layer of adhesive or facing F or other material is located between the facing F and the purlin lower flange PL. Thus, the facing F is deemed to be adhered to the purlin lower flange PL when adhered directly to the purlin lower flange PL and/or if the facing F is connected to and overlapped with another piece of facing F that is connected directly or indirectly to the purlin lower flange PL. 
       FIG. 6  shows an alternative carriage embodiment C′ that is identical to the carriage C, except that the first and second bases B 1 ,B 2  of the carriage C′ each include first and second roll support devices  20   a , 20   b  each defined as described above for the roll support devices  20 . With the carriage C′, the facing F must be dispensed from the roll RF behind the struts  16   a , 16   b  in terms of the carriage movement direction so as not to obstruct movement of the feet  12   a , 12   b  on the purlin flanges PL. As such, the respective first roll support devices  20   a  are adapted to support and dispense a roll of facing RF when the carriage is moving in direction D 1 , and the respective second roll support devices  20   b  are adapted to support and dispense a roll of facing RF when the carriage C is moving in the opposite direction D 2 . In one alternative embodiment, the second roll support devices  20   b  are each separately adapted to support and dispense double-sided tape from respective separate, individual rolls onto the bottom faces PF of the lower flanges PL of the purlins P 1 ,P 2 , with the first roll support devices  20   a  dispensing facing F from a roll RF to be adhered to the purlin lower flanges PL via the tape dispensed from the device  20   b  when the carriage C is moving in direction D 1  (if the carriage is moving in direction D 2 , the first roll support devices  20   a  are each separately adapted to support and dispense double-sided tape from respective separate, individual rolls onto the lower flanges PL of the purlins P 1 ,P 2 , with the second roll support devices  20   b  dispensing facing F from a roll RF). As an alternative to double-sided tape, the first roll support devices  20   a  (for moving in direction D 2 ) or second roll support devices  20   b  (for moving in direction D 1 ) can be replaced by or used to support devices for dispensing a spray or bead or other layer or deposit of liquid or other adhesive onto the respective lower flanges PL of the first and second purlins P 1 ,P 2 , after which facing F is adhered to the lower flanges PL as dispensed from a roll RF supported by the first roll support devices  20   a  (for moving in direction D 1 ) or second roll support devices  20   b  (for moving in the direction D 2 ). 
     It is not intended that the carriage C,C′ and/or roll support devices  20  ( 20   a , 20   b ) be limited to the embodiments shown. Also, the roll RF of facing F can include a core or be coreless, and can include the spindles  28  or not, and can include a central shaft extending therethrough or not, and the structure of the roll support devices  20  will vary accordingly in order to rotatably support the roll RF for dispensing facing F therefrom to be adhered to the purlin lower flanges PL in response to movement of the carriage C along the purlins P 1 ,P 2  in the direction D 1  or D 2 . 
       FIGS. 7-10  disclose another alternative carriage  2 C for implementing the system and method of the present development. Like components relative to the carriage C are identified with like reference numbers/letters. The base B comprises first and second base portions B 1 ,B 2  interconnected by adjustable-length cross-members XB. A first foot  12   a  is connected to the first base portion B 1  by a first strut  16   a , and a second foot  12   b  is connected to the second base portion B 2  by a second strut  16   b . The first and second feet  12   a , 12   b  are adapted to be slidably supported on and engaged with the lower flanges FL of the first and second purlins P 1 ,P 2 , respectively, for movably supporting the carriage  2 C for movement in the first direction D 1 . The first and second feet are pivotally connected to the respective struts  16   a , 16   b  by respective pivoting connections V (see  FIG. 10 ). 
     The base B is adapted to rotatably support a roll of facing RF for dispensing facing F from the roll for adhesive securement to the bottom surface PF of the purlin lower flanges PL. As shown, the roll RF is supported by use of spindles  28  in its ends, with the spindles  28  secured to the respective base portions B 1 ,B 2 . Alternatively, a rod or the like can extend between the base portions B 1 ,B 2  and the roll RF is rotatably carried on the rod. 
       FIG. 7  shows the base B in a free state, where the roll RF is not operably engaged with the purlins P 1 ,P 2 . In use, as shown in  FIGS. 8-10 , a user grasps the outermost cross-bar XB (farthest from facing roll RF) as a handle and pulls downward away from the purlins P 1 ,P 2  to pivot the base B such that the roll RF is moved upward into contact with the bottom faces PF of the lower flanges PL, while the user simultaneously pulls the carriage in the direction D 1  to dispense the facing F from the roll RF as described above. The facing includes first and second adhesive zones Z 1 ,Z 2  ( FIG. 7 ) that adhere the facing F to the purlins P 1 ,P 2  as the carriage is moved in the direction D 1 . As noted above, the facing is thereafter more permanently secured using screws or other fasteners that engage the purlin lower flange PL. For the carriage  2 C and all other embodiments disclosed herein, after the carriage is operably suspended from the purlins P 1 ,P 2 , the user can start the facing operation by pulling some facing from the roll RF and adhering same to the bottom face PF of the lower flanges PL. 
       FIG. 9A  shows the carriage  2 C with the adjustable-length cross-members XB extended in order for the base B to accommodate a roll of facing RF 1  having a width W 1  for a first purlin spacing distance.  FIG. 9B  shows the carriage  2 C with the adjustable-length cross-members XB retracted in order for the base B to accommodate a roll of facing RF 2  having a width W 2  for a second purlin spacing distance. 
       FIG. 11  shows an alternative carriage  2 C′ in which the roll support devices  20  of the carriage C are replaced by a roll support device  200  that comprises a frame  202  pivotally connected to the first and second base portions B 1 ,B 2  at pivot points V 1 ,V 2 . The frame  202  includes at least one and preferably first and second roll supports  204  ( 204   a , 204   b  as shown) on which a roll RF of facing F is rotatably supported for dispensing onto the purlin lower flanges PL as described above. As shown, the first and second roll supports  204   a , 204   b  comprise respective adjustable-length rods  205  on which the roll RF is rotatably supported. In the embodiment of  FIG. 11 , when a roll RF is carried by one of the roll supports  204   a , 204   b , the other roll support  204   a , 204   b  serves as a handle for grasping by a user to move the carriage to install the facing F from the roll RF with the installed facing F trailing the carriage C. In such case, the user also manually pivots the frame  202  relative to the base B of the carriage C about pivot points V 1 ,V 2  such that the roll RF is urged into contact with the purlin lower flanges PL. 
     The present development provides a system and method and device for facing a roof structure, i.e., for installing facing F on the underside of roof purlins P 1 ,P 2  by securing the facing F to the purlin lower flanges PL. It is not intended that the present development be limited to the exact designs for the carriages C disclosed herein. In general, the present development is intended to encompass any carriage that carries and dispenses facing F for securement of the facing F to the lower flanges PL of purlins P (P 1 ,P 2 , etc.) using adhesive such as tape or other adhesive, whether the tape or other adhesive is part of the facing, dispensed from the carriage and/or applied to the purlin flanges PL in a separate process before and/or after the facing is dispensed. 
     For all carriage embodiments, if desired or required for certain applications, the carriage can function merely as a dispenser for the roll of facing RF, meaning that the carriage can be operably suspended from the purlins P 1 ,P 2  and clamped or otherwise secured in position. Then the user can manually pull facing F from the roll RF and extend the facing along the length of the purlins P 1 ,P 2 , navigating the facing around pipes, electrical conduits and other obstructions while adhering the facing to the bottom faces PF of the purlin lower flanges PL. 
     The development has been described with reference to preferred embodiments. Those of ordinary skill in the art will recognize that modifications and alterations to the preferred embodiments are possible. The disclosed preferred embodiments are not intended to limit the scope of the following claims, which are to be construed as broadly as possible, whether literally or according to the doctrine of equivalents.