US20100031586A1

US20100031586A1 - Roof joist for modular building and methods

Info

Publication number: US20100031586A1
Application number: US12/482,430
Authority: US
Inventors: Mark Miller
Original assignee: Project Frog Inc
Current assignee: Project Frog Inc
Priority date: 2008-06-10
Filing date: 2009-06-10
Publication date: 2010-02-11

Abstract

A roof joist for a roof section of a modular building having an interior ceiling with a length, having an upper chord, central chord, and lower chord. The lower chord comprises: (i) a top chord segment joined to, and parallel with, the central chord; (ii) a pair of sidewall chord segments that oppose one another and extend parallel to the top chord segment; and (iii) a pair of outer flanges that extend outwardly from the sidewall chord segments to support the interior ceiling. A pair of inner flanges can also extend inwardly from the sidewall chord segments to support fixtures in the interior of the building.

Description

RELATED APPLICATION

This application claims the benefit of provisional application No. 61/060,399 filed Jun. 10, 2008, which is incorporated by reference herein in its entirety.

BACKGROUND

Embodiments of the present invention relate to a roof joist for a modular building.
Modular buildings are often made from pre-fabricated, portable building elements that are designed to facilitate shipment and assembly of a building structure at a building site. Modular buildings can also be transported in large preassembled sections and then connected at the building site. Such buildings reduce fabrication and assembly costs by allowing mass production and partial assembly of common parts and sections of buildings. They can also be rapidly deployed to replace damaged buildings after natural disasters, such as hurricanes and earthquakes. As such, modular building structures have unique design requirements which are different from conventional buildings. For example, modular buildings can be designed to allow flexible configurations for different types of external configurations and interior spaces. They can also be designed facilitate ease of assembly onsite and at a building location. Further, when used in disaster zones, replacement modular buildings often have to meet strict regional standards with respect to seismic resistance and storm-resistant structural frame.
The structural components and other parts for such modular building also have unique requirements. For example, the modular building components need to be designed to facilitate mass production and transport. Component shape standardization can also be used to reduce warehouse storage space required to keep a large number of prefabricated components. Further, modular parts should also be adaptable to allow for a wide variety of end use applications. In addition, it is desirable for a modular components to be adapted for multiple uses to reduce the number of components used in each building.
One component type that needs special attention in such building structures is the roof joist. A roof joist provides load-bearing capabilities to support the roof structure and resist shearing forces. A number of different types of roof joists have been used in building construction, including, for example, a simple I-beam structure made from structural steel. In some embodiments, roof joists are parallel beams made of timber, steel, or reinforced concrete beams, and are shaped and sized to support the roof of the building. However, many such embodiments of roof joists are heavy and difficult to transport or even to fabricate. They also have different, non-standardized designs that are not always readily adaptable to meet the standards of different building designs.
For reasons including these and other deficiencies, and despite the development of various roof joist structures and modular buildings, further improvements in roof joists and such buildings are continuously being sought.

SUMMARY

A roof joist can be used in a roof section of a modular building comprising an interior ceiling having a length. The roof joist comprises an upper chord comprising a length sufficiently long to extend substantially across the entire length of the interior ceiling of the roof section of the modular building. A central chord is joined to the upper chord. A lower chord is joined to the central chord. The lower chord comprises: (i) a top chord segment; (ii) first and second sidewall chord segments that extend downwardly from the top chord segment and oppose one another; and (iii) first and second outer flanges that extend outwardly from the first and second sidewall chord segments, respectively, the flanges being capable of supporting the interior ceiling.
A method of forming the roof joist comprises: (a) extruding a material to form an extrusion preform comprising an upper chord, a central chord joined to the upper chord, and a lower chord joined to the central chord, the lower chord comprising: (i) a top chord segment; (ii) first and second sidewall chord segments that extend downwardly from the top chord segment and oppose one another; and (iii) first and second outer flanges that extend outwardly from the first and second sidewall chord segments, respectively, the flanges being capable of supporting the interior ceiling; and (b) cutting the extrusion preform when the lengths of the upper, central and lower chords are each sufficiently long to extend substantially across the entire length of the interior ceiling of the roof section of the modular building.

DRAWINGS

These features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings, which illustrate examples of the invention. However, it is to be understood that each of the features can be used in the invention in general—not merely in the context of the particular drawings—and the invention includes any combination of these features, where:

FIG. 1A is a side sectional view of an exemplary embodiment of a roof joist for a modular building;

FIG. 1B is a perspective view of the joist of FIG. 1A;

FIG. 2A is a side sectional view of another embodiment of a roof joist for a modular building;

FIG. 2B is a perspective view of the joist of FIG. 2A;

FIG. 3A is a side sectional view of yet another embodiment of a roof joist for a modular building;

FIG. 3B is a perspective view of the joist of FIG. 3A;

FIG. 4 is a cross-sectional view of the joist of FIG. 3A showing inner flanges with support tabs for holding a device, and the outer flanges holding ceiling tiles;

FIG. 5 is a cross-sectional view of a roof section of a modular building showing integration of a roof joist into the structure;

FIG. 6 is a side view of a frame of a modular building comprising shed with tilted roof and side expansion module;

FIG. 7 is a perspective view of a frame of a modular building comprising a shed, side expansion modules, and a concrete grade beam foundation; and

FIG. 8 is a schematic perspective view of an embodiment of a modular building that uses a plurality of the roof joists to define a roof section, a ceiling supported by the roof joists, sidewalls, and a support sled.

DESCRIPTION

An exemplary embodiment of a roof joist 20 for use in a roof section 24 of a modular building is shown in FIGS. 1A and 1B. This roof joist 20 is multifunctional and can be used to both support a roof 26 of a modular building, retain a suspended interior ceiling 28 along the length of the roof section 24, and even support fixtures and other equipment that is used in the interior of the building. In the embodiment shown, the roof joist 20 comprises an upper chord 30, lower chord 32, and central chord 34. Each of the upper and lower chords 30, 32 are end members of the roof joist 20 and span across the entire length of the roof joist 20. The upper and lower chords 30, 32 are substantially parallel to one another, and are connected to each other by the central chord 34. In this illustrative embodiment, the upper chord 30, lower chord 32, and central chord 34 are each depicted as a single longitudinal structure; however, it should be understood that other structures equivalent to the longitudinal structures, such as a web of structural members (not shown), a plurality of beams (not shown), a honeycomb member (not shown), or other structures apparent to one of ordinary skill in the art, can also be used.
The upper chord 30 has a longitudinal segment 36 with a length sufficiently long to extend across substantially across the entire length of an interior ceiling 28 of the modular building 100. In one version, the upper chord 30 comprises a longitudinal segment 36 comprising a planar beam 38. The geometry of the planar beam 38 facilitates welding or fastening the roof joist 20 in-place to a roof structure. For example, a set of fasteners 40 comprising screws, nails or clips can be used to fasten the longitudinal segment 36 to a decking product 71, or to roof panels, roof panel brackets or even drainage channels.
The central chord 34 is joined to, and parallel with, the upper chord 30. In one version, as shown in FIG. 1A, the central chord 34 comprises a flat beam 46 oriented perpendicularly to the longitudinal segment 36 of the upper chord 30.
The lower chord 32 comprises a top chord segment 48 which is also joined to, and parallel with, the central chord 34. The top chord segment 48 can also extend across substantially the entire length of the interior ceiling 28 of the modular building 100. The lower chord 32 further comprises a pair of sidewall chord segments 50 a,b that oppose one another and extend parallel to the top chord segment 48. In one version, the lower chord 32 forms a U-shaped longitudinal channel 52 with its opening facing downward. In one version, the U-shaped channel 52 is rectangular, and has a depth of from about 2 to about 4 cm and a width of from about 4 to about 8 cm.
Each sidewall chord segment 50 a,b of the lower chord 32 supports an outer flange 54 a,b that extends outwardly from the sidewall chord segments 50 a,b. In one version, the outer flanges 54 a,b extend outwardly from the lower edge of the sidewall chord segments 50 a,b to serve as outwardly protruding load bearing surfaces. In one example, the outer flanges 54 a,b of the lower chord 32 are used to support a plurality of ceiling panels 76 which form an interior false ceiling 28 of the modular building 100 (see also FIG. 4). The false ceiling is useful for hiding electrical connections, plumbing, ventilation, and other such utilities. The false ceiling 28 can also be used to absorb sound or provide additional insulation. The ceiling panels 76 can be made from a rigid material that is, for example, thermally insulating, sound absorbing and/or decorative. In one version, the outer flanges 54 a,b are sized sufficiently long to support ceiling panels 76 to form an interior ceiling. In this example, each outer flange 54 a,b has a length of from about 2 to about 4 cm, extended to an adequate length to support the ceiling panels 76. The outwardly extending flange 54 a,b is also separated from the roof 26 of the structure by a distance of from about 12 to about 18 cm. This separation provides acoustic and thermal insulation between the interior and the exterior of the structure when the pair of outer flanges 54 a,b are used to support the false ceiling.
The sidewalls of the lower chord 32 can also have inner flanges 58 a,b that extend inwardly from the sidewall cord segments 50 a,b. The pair of inner flanges 58 a,b serve as support members to support fixtures 59, such as equipment and objects used in the interior of the building. For example, the inner flanges 58 a,b can be used to support fixtures 59 such as for example windows, sidewall panels, screens or even doors. In one version, the inner flanges 58 a,b extend inward from the sidewalls by between about ⅛ to about ⅓ of the diameter of the U-shaped channel 52 as defined by the lower chord 32. The channel 52 with inner flanges 58 a,b can also provide a location for universal attachment of user equipment, such as, for example, lighting, white boards or projection screens without the need for drilling, screwing or nailing into the structure. In one version, each inner flange 58 a,b of the lower chord 32 has a length which is sized smaller than a length of each outer flange 54 a,b. In one version, each inner flange 58 a,b comprises a length of from about 1 to about 3 cm, or even about 2 cm. This length is suitable for providing load-bearing support surface for sidewall panels or other support-tab-equipped fixtures.
In another embodiment, as shown in FIGS. 2A and 2B, the roof joist 20 comprises a plurality of longitudinal hollow channels 60 a,b that form separately enclosed reinforcing structures. In this version, the upper chord 30 comprises a first longitudinal hollow channel 60 a having a box shape and defining a first enclosed volume 62 a. The central chord 34 also comprises two opposing sidewall members 34 a,b that are parallel to one another and join the upper chord 30 and the lower chord 32 to also form a second longitudinal hollow channel 60 b, which has a box shape and defines a second enclosed volume 62 b. The top chord segment 48 forms a common wall between the lower chord 32 and the central chord 34.
The first and second longitudinal hollow channels 60 a,b serve as reinforcing structural members that allow the roof joist 20 to accommodate the structural load of the ceiling with a minimal of structural material and weight. This structure decreases the weight of each roof joist 20 and the lower weight also facilitates transportation of the joists. The hollow longitudinal channels 60 a,b also have dual function in that, in addition to serving as a support for roof and ceiling panels, they also provide an enclosed hollow leakage-containing structure to retain moisture seepage from the ceiling or sidewalls without allowing permeation of this moisture into the building. For example, fasteners such as screws or clips can be attached into or even through the longitudinal segment of the joist 20 without risk of leakage into the building. The sidewalls of the second hollow channel 60 b can be drilled and fastened to provide support points for wires or electrical connections, plumbing, ventilation or other utilities while substantially reducing risk of moisture seepage from the first hollow channel 60 a.
In one version, the second enclosed volume 62 b is sized larger than the first enclosed volume 62 a. For example, the second enclosed volume can be at least 1.5 times larger than the first enclosed volume. A ratio of 1.5 provides a reduced region for external water containment which can subject the beam to a greater structural load. In addition, the ratio of the first and second volumes serves to provide a selectively larger region for the fastening of internal or external components to the joist 20. For example, increasing the volume ratio from 3:2 to a volume ratio of 4:1 allows a greater surface area for drilling and fastening of interior components to the joist 20.
In still another version, as shown in FIGS. 3A and 3B, the roof joist 20 comprises a single longitudinal hollow channel 60 that forms an enclosed reinforcing structure. In this version, joist 20 comprises an upper chord 30 comprising a planar beam 38, and a lower chord 32 comprising a top chord segment 48. The top chord segment 48 of the lower chord 32 is joined to the planar beam 38 of the upper chord 30 by a plurality of central chords, such as the pair of flat beams 46 a,b. The flat beams 46 a,b are oriented perpendicular to the longitudinal segment 36 of the upper chord 30. The hollow channel 60 is bounded by the top chord segment 48, the flat beams 46 a,b and the planar beam 38. The hollow channel 60 can serve as a reinforcing structural member and can even provide an enclosed hollow leakage-containing structure if an exterior wall of the channel 60 is punctured. For example, if the planar beam 38 is drilled and fastened with roof tiles or roof tile support brackets, the hollow channel 60 receives seepage from the roof and prevents permeation of this moisture into the building.
The inner flanges 58 a,b can have a shaped surface to reduce accidental slippage of load-bearing support tab 78. In one version, each of the inner flanges 58 a,b are equipped with an inner ridge 82 a,b, respectively. In this version, the inner ridges 82 a,b can, for example, extend upward from the load-bearing surface by a distance of from about 0.1 to about 0.5 cm. As shown, the inner ridges 82 a,b can have a cross-sectional profile that is triangular (as shown in FIG. 3A) or circular or U-shaped (as shown in FIG. 4). A triangular cross-sectional profile can allow the inner ridges 82 a,b to contact the downward facing surface of support tab 78 over a reduced area and form an indentation in the support tab 78 when the tab is made of a material that is more ductile than the lower chord material and is subjected to load.
Alternatively, the load-bearing upper surface of each inner flange 58 a,b and the downwardly facing surface of the support tab 78 can be shaped to mate together as shown in FIG. 4. For example, the support tab 78 can comprise a rotatable brad having grooves 80 a,b to correspond with the ridges 82 a,b. When the support tab 78 is installed in the U-shaped channel 52, the grooves 80 a,b of the support tab 78 mate with the ridges 82 a,b of the inner flanges 58 a,b. The support tab 78 having grooves 80 a,b that correspond with the ridges 82 a,b of the U-shaped channel 52 is harder to rotate under load and has a reduced chance of slippage from the U-shaped channel 52.
The roof joist 20 can be fabricated by a number of different methods. In one version, the roof joists 20 comprise a shaped extruded structure which has a consistent cross-sectional shape throughout its length. In this method, the roof joist 20 is formed by extruding a material to form an extrusion preform comprising upper chord 30, a central chord 34 joined to the upper chord 30, and a lower chord 32 joined to the central chord 34, the lower chord 32 comprising: (i) a top chord segment; (ii) first and second sidewall chord segments 50 a,b that extend downwardly from the top chord segment 48 and oppose one another; and (iii) first and second outer flanges 54 a,b that extend outwardly from the first and second sidewall chord segments 50 a,b, respectively, the flanges being capable of supporting the interior ceiling 28. The extrusion preform is cut when the length of the upper, central and lower chords 30, 34, 32 are each sufficiently long to extend substantially across the entire length of the interior ceiling 28 of the roof section 24 of the modular building 100. However, it should be noted that the roof joist 20 can also be made by other non-extrusion methods, for example: cutting and welding of metal tube and sheet stock, bending and welding of multiple formed parts, and pultrusion, as would be apparent to those of ordinary skill in the art.
The roof joist 20 can be made from a metal, including steel, aluminum, iron, tin, or alloys thereof. The roof joist 20 can also be made from a polymer or composite material. In one example, the roof joist 20 is made from extruded aluminum which is lightweight, strong and relatively flexible. The roof joist 20 can also be made from a reinforced composite material, such as carbon or polyimide fibers in an epoxy matrix.
The roof joist 20 can be used in any building, including a modular building 100 that is rapidly deployable, easily transportable, and which is designed to minimize on-site assembly, as shown in FIGS. 5 to 7. In such a building, a plurality of spaced-apart roof joists 20 form trusses that support the roof 26 by spanning the width between the ceiling beams. The roof joist 20 comprises features that allow for the attachment of trim pieces that can protect the modular building 100 from the elements and even add to the building's modern design aesthetic. Said mounting features can be manifested in a variety of forms, such as a plate that is welded to the end of the joists with holes for screw attachment, attachment features that are continuously extruded through a roof joist profile, or a clip attachment that is screwed or welded to the roof joists (not shown). The roof joist 20 can also be used to span from the ceiling beams to the headers of outer walls. Further, roof joists 20 a which are positioned at the outer edge of the ceiling can have outer flanges 54 a,b which allow for the attachment of externally located roof drainage channels 74 (as shown in FIG. 5), plumbing, or even electrical conduits.
The roof joist 20 supports a roof 26 which can be a variety of different structures. For example, a decking product 71 can be attached to the top of a roof joist 20 to form a rigid surface that supports a roof section 24, as shown in FIG. 1A. For example, the decking product 71 can be a corrugated, screw-fastened or welded decking product. The decking product 71 can be fastened to the roof joist 20 to form a continuous rigid surface. The roof material can be, for example, insulation or roof membrane materials.
Alternately, the roof 26 can comprise roof panels 70 that are fastened directly to the longitudinal segments 36 of the roof joists 20 or that are fastened to the joists 20 through intermediary roof panel brackets 72. An embodiment of a roof structure having intermediary roof panel brackets 72 and roof panels 70 is shown in FIG. 5. The roof panel 70 shown comprises a shaped panel with attachment flanges and arcuate top surface. The ends of the roof panel 70 slope downward towards a drainage channel 74 that is mounted on an end roof joist 20 a. The roof panel 70 can even be an interlocking panel that is equipped with grooves to snap-fit or otherwise interlock with other roof panels 70 to form a continuous rigid roof structure.
The roof joists 20 and roof 26 are used to cover the structural frame of a modular building 100 as shown in FIGS. 6 and 7. The modular building 100 comprises a sled 102 supporting a shed 104 with side expansion modules 106. The sled 102 comprises a rectangular frame composed of wide-flange beams 126 that are spaced apart and rest on underlying an concrete grade beams 124. The wide-flange beams 126 are oriented in a rectangular configuration and are joined to one another by high-strength bolts 128. The sled 102 can be anchored into the concrete grade beams 124 and leveled using cast-in-place or post-poured, drilled, high strength bolts. The wide-flange beams 126 can even be equipped with custom mounting surface such as welded flat plates 130 that enable them to be mounted to the concrete grade beams 124. The concrete grade beams 124 can be oriented to provide a hollow region underneath the sled 102 for placement of prefabricated electrical and ventilation system components. The constructed sled 102 provides a preassembled structural platform with good structural integrity, pre-tested bolted and welded connections, and which allows a flexible configuration of any overlying shed 104.
Floor joists 132 extend across the upper surface of the sled 102 to provide a floor having structural rigidity and without seams. The floor joists 132 can comprise conventional tubular sections or beams. A raised floor 134 is formed from floor panels 136 placed between the framework of the floor joists 132 to provide the necessary structural diaphragm for the base of the shed 104. As one example, the floor panels 136 can be made from structural metal decking. As another example, the floor panels 136 can be composed of concrete-filled metal pans that sit on pedestals so that the underlying cavity can house electrical and mechanical services. The floor panels 136 can also be rearranged to move outlets, ports, and air diffusers, providing the user with maximum flexibility. The under-floor distribution of mechanical services for the overlying shed 104 can include HVAC (heating, ventilation and cooling) tubes, electrical junction boxes and preassembled wiring. Locating electrical and mechanical services underneath the floor 134 of the shed 104 provides an integrated infrastructure for such services and can be tailored without extensive pre-wiring and ventilation planning for the overlying shed 104.
The shed 104 placed on the sled 102 comprises a steel framework of spaced-apart columns that are linked to one another by overhead roof joists 20 and trusses 110, as shown in FIGS. 6 to 7. The joists 20 and trusses 110 provide a rigid structural roof section 24 with large spans that has minimal material usage while providing a highly flexible and tailorable interior space. The columns of the shed 104 can include major columns 114 located at the corners of the shed 104 and attached to the overlying beams of the sled 102 by gussets to provide vertical strength in support of the ceiling. Minor columns 116 are bolted to the floor joists 132 of the sled 102. In addition, diagonal columns 118 comprising 4×4 structural tubes can also be used to brace the structure of the shed 104 and increase its lateral and shear strength. All these tubes are linked together with tube steel headers 120 and bolted together for greater strength.
The minor columns 116 can be spaced apart a sufficient distance to accommodate wall panels, such as light-impermeable panes 186, light-permeable panes 188, such as windows, translucent screens or even doors. Advantageously positioning the minor columns 116 a predefined spacing distance provides a highly adaptable exterior sidewall for the shed 104, so that each exterior sidewall can be adapted to allow the transmission of light, serve as an opaque wall, or even provide an integrated connection of the interior space of the shed 104 to other structures, such as an expansion module 106. The structure of the shed 104 also enables the two long exterior sidewalls to be absent—structural reinforcements which are conventionally needed to provide strength in seismic or storm locations—consequently enabling the shed 104 to have a variety of different external wall configurations.
The expansion module 106 comprises a steel frame designed to be attached to an open sidewall or end wall of a shed 104 to expand the usable enclosed space provided by the shed 104. For example, the expansion module 106 can comprise major columns 114 that form the corners of its structural frame, at least two of the columns being external to the shed 104 and two other columns being integrated into a sidewall of the shed 104. The expansion module 106 also has a sidewall with minor columns 116 that can be spaced apart as described in the minor columns of the shed 104 to allow spaces for light-permeable panes 188, doors, or other structures. A single wide-flange beam 126 bolted to a concrete grade beam 124 can be used to support the outside sidewall of the expansion module 106. The expansion modules shown in FIG. 7 extend outward perpendicularly from the shed; however, alternate arrangements are possible, such as wedge-shaped side expansion modules, as shown in FIG. 8.
The ceiling or roof plane of the modular building 100 can have variable heights and provide optional clerestory natural lighting. As a result, the modular building 100 can be tailored to a wide range of interior environments while still providing a quick-to-deploy modular building that is safe and long-lasting. For example, the shed 104 can comprise a roof 26 comprising a tilted support structure 122 that can be equipped with clerestory windows along the triangular gap between the roof plane and the shed sidewall, as shown in FIGS. 6-8. The tilted support structure 122 has a plurality of vertical and diagonal struts that allow for mounting of light-permeable panes in a clerestory configuration. In one embodiment, the tilted roof support is mounted to the major columns 114 of the shed 104 with hinges that allow for the tilted roof support to be folded down to lie flat against the roof of the shed. The hinged tilted roof support allows for the roof of the modular building to be lowered into a horizontal position during periods of high wind conditions, which might occur during transportation of the shed 104 by truck to the building site.
The roof structure comprises trusses 110 that rest on and are anchored to the steel frame of the underlying shed 104 or the frame of the expansion module 106. The trusses 110 can be steel or aluminum beams or even composite support beams. The trusses are equipped with attachment surfaces 112 for fastening of roof joists 20, which span the length between trusses 110, as shown schematically in FIG. 5. The truss and joist ceiling structure can provide support for a closed roof 202 and is even suitable to provide a high-strength structure for situations such as storm or high snow environments.
The ceiling 220 of the expansion module 106 can be an open ceiling or an enclosed ceiling formed by ceiling joists 20. The ceiling joists 20 are spaced apart a set distance of 4 feet, for example, and linked at their ends to the ceiling beams which are connected to one another and the major and minor columns 114, 116. The structure provides a rigid framework which also allows easy expansion of the interior space provided by the shed 104 while providing good structural strength.
Each of the sled 102, shed 104, and expansion modules 106 comprise a structural frame of modular building components, and they are transported onto a building site with essentially all labor-intensive and inspection-intensive work—such as welding, drilling and cutting—already completed. This allows a modular building 100 composed of the sled 102, shed 104, and optional expansion modules 106 to be quickly assembled on the site to provide a fully integrated housing structure. The pre-manufactured structural components comprise a “kit of parts” that only need to be joined or partially assembled without extensive onsite alterations to provide a high performance structure with an adaptable interior configuration. The structures also reduce risks associated with improper assembly by requiring only minimal skill levels for assembly and equipment usage. The assembled modular building 100 can also withstand the vertical and lateral forces generated in earthquakes and storms. Further, the structures also reduce or eliminate onsite construction waste as leftover materials remain at the factory for recycling.
An exemplary embodiment of a modular building 100 is shown in FIG. 8; however, many other configurations are possible and can be preferred for any specific application, as would be apparent to one skilled in the art. In the embodiment of FIG. 8, the modular building 100 comprises a structure that includes a supporting sled 102, a shed 104, and two expansion modules 106. The sled 102 serves as a support and base for the shed 104 and can also be used to provide preassembled electrical connections for electrical services and mechanical services, such as ventilation, heating, cooling and water plumbing. The shed 104 provides an enclosed housing structure that rests on the sled 102 which serves as the interior space of the modular building 100. The expansion modules 106 can be used to expand the interior space of the modular building 100 to provide extra space and to contain facilities such as restrooms, electrical power equipment or other building service equipment. In the diagram shown, the sled 102, shed 104, and expansion modules 106 have rectangular structures; however, it should be understood that other shapes and structures—for example, cylindrical or spherical structures—can also be used as would be apparent to those of ordinary skill in the art. Thus, the scope of the invention should not be limited to the illustrative embodiments described herein.
The modular building 100 can be customized to include additional components. For example, a handicapped access ramp 135 comprising a rigid tilted surface 137 and handrails 138 can be provided at an entrance to the shed 104. The access ramp 134 can be configured to allow passage of wheeled devices, such as wheelchairs and strollers, from ground level outside of the modular building 100 to the interior of the shed 104. A sun shade structure such as awning 142 can be provided to filter or even block direct sunlight to some or all of the side panels of the modular building 100. Solar panels 140 can be mounted on or even integrated into the roof structure or can be supported on peripheral structures such as awning 142. Finally, a green roofing material 144 capable of filtering pollutants from the surrounding air can be provided for example, a layer of plants.
While illustrative embodiments of roof joist 20 are described in the present application, it should be understood that other embodiments are also possible. For example, the roof joist 20 can have other shapes and structures and can be made from other materials, as would be apparent to those of ordinary skill in the art. Thus, the scope of the claims should not be limited to the illustrative embodiments described herein.

Claims

1. A roof joist for a roof section of a modular building, the modular building having an interior ceiling with a length, and the roof joist comprising:

(a) an upper chord comprising a length sufficiently long to extend substantially across the entire length of the interior ceiling of the roof section of the modular building;

(b) a central chord joined to the upper chord; and

(c) a lower chord joined to the central chord, the lower chord comprising:

(i) a top chord segment;

(ii) first and second sidewall chord segments that extend downwardly from the top chord segment and oppose one another; and

(iii) first and second outer flanges that extend outwardly from the first and second sidewall chord segments, respectively, the flanges being capable of supporting the interior ceiling.

2. A roof joist according to claim 1 wherein the upper chord comprises a longitudinal and planar beam.

3. A roof joist according to claim 2 wherein the central chord comprises a flat beam that is perpendicular to the longitudinal and planar beam of the upper chord.

4. A roof joist according to claim 2 wherein central chord comprises two opposing sidewall members that are parallel to one another.

5. A roof joist according to claim 1 wherein the upper chord comprises a first longitudinal hollow channel having a first enclosed volume.

6. A roof joist according to claim 5 wherein the central chord comprises two opposing sidewall members that are parallel to one another and define a second longitudinal hollow channel having a second enclosed volume, and wherein the second enclosed volume is sized larger than the first enclosed volume.

7. A roof joist according to claim 6 wherein the first and second enclosed volumes each comprise a rectangular cross-section.

8. A roof joist according to claim 1 further comprising first and second inner flanges that extend inwardly from the first and second sidewall chord segments, respectively.

9. A roof joist according to claim 8 wherein a length of each of the first and second inner flanges of the lower chord is smaller than a length of an outer flange.

10. A roof joist according to claim 9 wherein each outer flange is sized from about 2 to about 4 cm.

11. A roof joist according to claim 9 wherein each inner flange is sized from about 1 to about 3 cm.

12. A roof joist according to claim 8 wherein each inner flange comprises an inner ridge.

13. A modular building comprising a roof section defined by a plurality of the roof joists of claim 1, a ceiling supported by the roof joists, sidewalls, and a support sled.

14. A method of forming a roof joist for a roof section of a modular building having an interior ceiling with a length, the method comprising:

(a) extruding a material to form an extrusion preform comprising an upper chord, a central chord joined to the upper chord, and a lower chord joined to the central chord, the lower chord comprising:

(i) a top chord segment;

(iii) first and second outer flanges that extend outwardly from the first and second sidewall chord segments, respectively, the flanges being capable of supporting the interior ceiling; and

(b) cutting the extrusion preform when the lengths of the upper, central and lower chords are each sufficiently long to extend substantially across the entire length of the interior ceiling of the roof section of the modular building.

15. A method according to claim 14 wherein the material comprises a metal.

16. A method according to claim 15 wherein the metal comprises steel, aluminum, iron, tin, or alloys thereof.

17. A method according to claim 14 wherein the material comprises a polymer or composite material.

18. A method according to claim 14 wherein the material comprises a reinforced composite material.