AU675675B2 - Roof structure - Google Patents

Description

k P/o/o0 1 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "ROOF STRUCTURE" The following statement is a full description of this invention, including the best method of performing it known to the Applicant:- This invention relates to roof structures for relatively small buildings such as dwellings, sheds, small commercial buildings and the like, wherein the structure comprises a plurality of load bearing trusses spanning between and supported at or near their ends by spaced apart (usually external) walls of the building.

DESCRIPTIC' OF THE PRIOR ART Such roof structures, be the trusses made from timber or metal, have become popular of late, because the trusses may be prefabricated in the factory by mechanised processes. This enables the roof structure to be erected using less skilled and expensive on-site labour than is needed for more traditional structures that are fabricated on site by tradespeople.

The present invention relates more particularly to supporting structures for hipped roofs, that is to say roofs for a rectangular or square area that comprise at least three planar sections of roof covering; the first and second of which sections slope upwardly from corresponding side edges of the roofed area, to meet along a ridge line (when the roofed area is rectangular) or at an apex point (when the roofed area is square); and the third of which slopes upwardly from an end edge of the roofed area to the near end of the ridge line or the apex point, as the case may be.

S• Two so-called hip rafters coincide with the lines of intersection of the first and second sections with the third, that is to say a hip rafter extends from each corner of the roofed area to the near end of the ridge line or the apex point.

There are two types of trusses used in such roofs, namely full or complete trusses and truncated trusses. Complete trusses are essentially triangular, with two top chords rising to an apex from opposite ends of a bottom chord, whereas truncated trusses are 20 shallower, with a top chord comprising a centre portion, parallel to the •.."bottom chord, replacing the apex and flanked by inclined end portions extending from its ends to corresponding ends of the bottom chord.

The first and second sections of covering comprise the top chords of complete trusses, end portions of the top chords of truncated trusses, battens and cladding elements, whereas the third section comprises rafters supported by centre portions of the top chords of truncated trusses, battens and cladding elements.

In such roofs, the trusses (both full and truncated) are arranged in an array of spaced apart, mutually parallel trusses, each extending from one side edge of the roofed area to the opposite side edge. The apices of the complete trusses coincide with the ridge line of the roof, and the slope of their top chords corresponds to the slope of the first and second sections of covering. They may be few in number, depending on the length of the ridge line. Indeed in the case of a square roofed area there may be only one complete truss, or maybe none at all.

As the trusses of the array advance beyond the end of the ridge ooo line or apex point towards the end or third edge of the roofed area, they are truncated and become successively shallower, so as to accommodate the slope of the third section of covering, which the horizontal centre parts of their top chords underlie.

o. There is a practical limit to the extent to which the trusses may be truncated, and as a general rule the last two or three positions in the truss array adjacent the end edge of the covere, aa are unable to be filled with trusses matching the other trusses in so far as the cross- 20 sectional dimensions of their structural members and the nature of the •.."joints between them are concerned.

SUMMARY OF THE INVENTION As a result, it is usual for the last few positions in the array, that is to say in the area underlying the lower edge margin of the third section of roof covering, to be devoid of trusses and for non-standard arrangements to be on-site for the support of the roof covering adjacent that third edge of the roofed area.

Alternatively, the lower end portions of the hip rafters may be strengthened so that they are strong enough to support so called jack rafters spanning from the hip rafters to the end portions of the side and end edges of the roofed area.

Both of those expedients are inefficient and incompatible with the desire to use uniform components throughout and to pre-fabricate as much of the roof structure as possible before it is delivered to the building i lo site.

roTherefore, an object of the present invention is to provide a hipped i roof structure that comprises component sub-assemblies for the support of the roof covering adjacent to the edge of the roofed area that is parallel to the roof trusses, which sub-assemblies may conveniently be made 15 from stock material that is the same as or similar to that used in the remainder of the roof structure's sub-assemblies. It follows that roof structures according to the invention are more amenable to the mechanised pre-fabrication of all their parts than has been the case hitherto.

The invention consists in a hipped roof structure comprising at least one truncated truss, itself comprising a horizontal bottom chord and a top chord comprising a horizontal centre part flanked by two sloping parts, said at least one truss extending across a roofed area in a direction substantially parallel to an end boundary wall thereof, a beam extending from said bottom chord to said end boundary wall, and at least one a 4A truncated truss end portion extending from said beam to a side boundary wall of said area, wherein said truncated truss end portion comprises a sloping top chord part, a horizontal top chord part, a horizontal bottom chord part and a post extending from said bottom chord part to said horizontal top chord part; the slope of said sloping top chord part being the same as that of a said sloping part of the top chord of said at least one truncated truss.

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55\ *oo *o• BRIEF DESCRIPTION OF THE DRAWINGS By way of example, an embodiment of the above described invention is described in more detail hereinafter with reference to the accompanying drawing, being a diagrammatic perspective view of part of a hipped roof structure according to the invention.

BEST MODE OF CARRYING OUT THE INVENTION The illustrated roof structure is that of a hipped roof covering one end of a rectangular area bounded in part by two side walls and an end wall. Load bearing top plates 1, 2 and 3 respectively of the three walls are indicated in ghost outline in the drawing.

The roof covering is supported by a plurality of trusses extending *from side wall plate 1 to side wall plate 2. Those of the trusses that are closer to the end wall plate 3 than is the apex of the roof or the nearer end 7 of the ridge line of the roof, are truncated in known manner. The nearer each truncated truss is to the wall plate 3 the shallower it becomes. For the sake of clarity of the drawing, of all the trusses referred to above, only the shallowest truncated truss is shown. It comprises a bottom chord 4 and a top chord comprising sloping end parts 5 and a horizontal centre part 6. The truncated truss would of 20 course include internal members dividing it into a series of triangles in known manner, but to further simplify the drawing these conventional details, which form no part of the invention, have been omitted.

The inclined top chords or top chord parts (such as part 5) of the trusses function as the rafters of the first and second sections of the roof coverings, whereas hip rafters 8 and jack rafters (not shown) extending from the hip rafters 8 to the end wall plate 3 are provided in respect of 6 the third section of roof covering. The hip rafters 8 are supported near the apex or ridge of the roof by the truncated trusses, but, in conventional structures, are usually required to span without support from the top chord part 6 of the shallowest truncated truss to the end wall plate 3. This duty is the more onerous because each of the hip rafters supports the inboard ends of those of the jack rafters of two sections of the roof covering joined to each hip rafter 8 at places between the top chord part 6 and one end of the wall plate 3. This has required the hip rafters to be strengthened for this part of their span (resulting in them being over designed elsewhere), or has required other modifications to be made that has militated against the use of components in these corner areas of the roof that are uniform in nature o with those used elsewhere, creating the problem which the present S"invention addresses.

i. 15 In accordance with the invention a beam 9 is provided near each end of the lower chord 4 extending from that chord to the wall plate 3 together with, in this instance, two truncated truss end portions and 11.

Each of the truss end portions 11 comprises a sloping top chord part 12, a horizontal top chord part 13, a bottom chord part 14 and a post 15. The slope of the top chord part 12 is the same as that of the sloping parts of the top chords of the truncated trusses, and may be used in exactly the same way as rafters of the first or second section of roof covering. Likewise the horizontal top chord part 13 supports a hip rafter 8 in the same way as do the horizontal centre parts of the top chords of the truncated trusses.

7 The truss end portions 10 function in the same way as portions 11 and need no further description. It will be seen that each of them also supports a hip rafter 8.

Thus the truss end portions 10 and 11 may be made from the same stock material as are the trusses generally, and likewise may be pre-fabricated before delivery to site.

Each beam 9 is preferably a side member of a pre-fabricated ceiling support panel comprising that member, another side member 16, an end member 17 and a plurality, in this instance two, of ceiling joists 18. The joists 18 may function as supports for ceiling sheets.

This has the benefit over the prior art, in which such joists necessarily ooooo extend from the lower chord 4 to the wall plate 3, that they are substantially parallel to the lower chords of the trusses. This facilitates the affixture of the ceiling sheets as a whole in a uniform manner.

For preference the end member 17 of the ceiling panel has two lugs (not shown) projecting from it that are adapted to rest on the top of the lower chord member 4. This facilitates the emplacement of the panel and its support until and while the erector is fastening it in position.

Claims (6)

1. A hipped roof structure comprising at least one truncated truss, itself comprising a horizontal bottom chord and a top chord comprising a horizontal centre part flanked by two sloping parts, said at least one truss extending across a roofed area in a direction substantially parallel to an end boundary wall thereof, a beam extending from said bottom chord to said end boundary wall, and at least one truncated truss end portion extending from said beam to a side boundary wall of said area, wherein said truncated truss end portion comprises a sloping top chord part, a lo horizontal top chord part, a horizontal bottom chord part and a post extending from said bottom chord part to said horizontal top chord part; the slope of said sloping top chord part being the same as that of a said sloping part of the top chord of said at least one truncated truss. i:

2. A roof structure according to claim 1 wherein said beam is a side 15 member of a ceiling support panel spanning from said bottom chord to o: said end boundary wall. a

3. A roof structure according to claim 2 wherein said ceiling support panel further comprises a second side member spaced from said beam, an end member secured to said bottom chord, and at least two ceiling joists extending from said beam to said second side member.

4. A roof structure according to claim 1 further comprising a hip rafter supported by said truncated truss end portion, a first plurality of jack rafters extending from said hip rafter to said end boundary wall, and a second plurality of jack rafters extending from said hip rafter to said side boundary wall. i 9 A roof structure according to claim I wherein said truncated truss end portion is fabricated from component parts of the same material and cross-section as corresponding parts of said at least one truncated truss.

6. A method of making a roof structure according to claim 1 comprising the steps of prefabricating said at least one truncated truss, said beam and said truncated truss end portion as individual components at one location, transporting those components to a second location and assembling said structure at said second location from those components.

7. A method of making a roof structure according to claim 2 comprising the steps of prefabricating said at least one truncated truss, said ceiling support panel, and said truncated truss end portion as individual components at one location, transporting said components to a second location, and assembling said structure at said second location 15 from those components. S o Date: 4 December 1996 Applicant JOHN LYSAGHT (AUSTRALIA) LIMITED Attorney ROBERT G. SHELSTON F.I.P.A.A. of CARTER SMITH BEADLE f;\specs\11426 o ABSTRACT A hipped roof structure comprises a plurality of truncated trusses which become successively shallower as they approach an end of the roofed area. At least one beam extends from the bottom chord (4) of the shallowest truss to an end wall top plate which beam is a side member of a ceiling support panel (15,16,17 18). Two truncated truss end portions (10,11) extend from the beam to a side wall top plate and support a hip rafter which in turn supports jack rafters extending tF the walls. This enables all the components to be standardised and readily pre-fabricated for on site assembly. a a 0 f 9 a a ao* a aaa *oo o o o*