TIMBER ROOF TRUSS

THIS INVENTION relates to a timber roof truss. In particular, it is directed to a timber roof truss in which both upper and lower chords may be curved.

Throughout this specification, unless the contrary is expressly stated, where a document, act or item of knowledge is referred to or discussed, this reference or discussion i$ not an admission that the document, act or item of knowledge or any combination thereof was, at the priority date, publicly available, known to the public, part of the common general knowledge, or known to be relevant to an attempt to solve any problem with which this specification is concerned.

A roof truss, especially one used to support the roof of a residential structure, is typically manufactured from timber and comprises upper and lower chords connected by webs extending therebetween, Such a truss is a simple triangle using standard timber sections set on edge with the webs creating a combination of smaller triangles to provide the required rigidity; the upper chord(s) extend beyond where they converge with the lower chord(s) to provide any required eave overhang.

There are a number of disadvantages with such a truss which include (a) it is not possible to create readily a curved ceiling or roof outline as a complex combination of triangles is necessary to approximate the shape required; (b) it is difficult to achieve a smooth curve .as supporting battens must be individually adjusted on site using various curved templates; (c) the truss has little lateral stiffness or vertical stability during building construction and thus temporary cross bracing has to be provided until all battening is completed; (d) with truss members set on edge, only limited width is available for fixing of

battens which may require special care on assembly, or additional fittings, especially at butt joints, to avoid weakening the structure; (e) this minimal width can also prevent the use of industry standard tie down bolts and thus more complicated metal straps and/or brackets are required for the truss assembly; (f) for wider eaves, or for constructions in high wind zones, non- standard top chords or other methods of strengthening are required. All of the above disadvantages lead to increased construction costs.

In the prior technology, attempts have been made to address at least some of the above disadvantages by (a) use of specially fabricated unique timber beams or (b) by replacing timber trusses with trusses manufactured from metal, particularly steel and aluminium. However, a metal truss requires relatively sophisticated machinery to manufacture and assemble into the required shape, is not particularly environmentally friendly and still requires similar segmentation as discussed above with respect to a timber truss to approximate curves. Consequently, these prior technology solutions have generally been limited to expensive custom-designed homes,

It is thus a general object of the present invention to overcome, or at least ameliorate, one or more of the above-mentioned disadvantages.

According to a first aspect of the present invention, there is provided a roof truss manufactured from timber, said truss including:

a lower chord;

at least one upper chord; and

webs extending between and connecting together said lower chord and a respective said upper chord;

characterized in that said lower chord and/or at least one of said upper chord are of a curved configuration.

Preferably, said timber for said lower and upper chords is set on the flat,

Preferably, each said lower chord and each said upper chord are of a curved configuration,

Preferably, each said lower chord and said upper chord, when of a curved configuration, comprise a multiple of timber laminates,

Optionally, additional laminates can be incorporated where said upper and said lower chords converge to provide additional strength to said truss,

Optionally, said lower chord can be in multiple sections and joined to form a continuous chord.

Said timber laminates may be laminated together using one of more fixing means selected from the group comprising nails, screws, ripple pins and adhesive.

Said connecting together of said lower chord and a respective said upper chord may be by a nail plate,

As a second aspect of the present invention, there is provided a method of manufacturing a truss as hereinbefore described, said method including:

providing a said lower chord;

providing at least one said upper chord, and

connecting together said lower chord and a respective said upper chord with said webs, said webs of dimensions to restrain said lower chord and/or said at least one upper chord to a curved profile,

A third aspect of the present invention is the provision of a roof structure which includes:

a multiple of said truss as hereinbefore described assembled to provide a framework for a roof; and

one or more battens affixed to the upper surface of at least one of said upper chord for supporting sheet material thereon,

Said roof structure may also include one or more battens affixed to the undersurface of said lower chord for supporting sheet material thereon,

Optionally, the said roof structure may be adapted to enable fitting of a tie- down bolt or the like.

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings wherein;

FlG. 1 is a schematic representation of a structure which includes a truss constructed according to the invention;

FIG. 2 is a sectional view of the structure of FfG. 1 along the line A-A; and

FIG. 3 is a sectional view of the structure of FIG. 1 along the line B-B.

The truss (1 ) comprises a two-section lower chord 2(a,b), a first upper chord (3), a second upper chord (4), a series of connecting web members (5) and connecting plates (6),

Each chord (2,3,4) and web member (5) comprises two layers of straight timber laminated together using any conventional securing means known in the art such as nails, screws, ripple pins and similar mechanical fixings, or adhesive. The timber is set on the flat,

£ach connecting plate (6) is any suitable nail plate or similar known in the art.

The dimensions of each chord (2,3,4) and web member (5) are selected such that, on assembly to form the truss (1 ), the two sections 2(a,b) can be butt- jointed to form a continuous lower chord, and each chord (2,3,4) is restrained to a curved profile by suitable length of the appropriate web members (5), the web members (5) being held to the respective chords (2,3,4) using the connecting plates (6). Where the lower chord 2(a,b) and respective upper chord (3,4) meet, the resultant four-ply laminate (7,8) can be secured together with additional mechanical fixings.

Where the radii of the chords (2,3,4) are approximately 10m, (a) the four-ply laminate (7,8) junction of the chords (2,3,4) enable external eaves of approximately 1 ,4m to be created; (b) the trusses can be at 1800mm or 2400mm spacing, rather than the 900mm or 1200m spacing of conventional

triangular timber trusses; and (c) conventional flat roof sheeting can be readily attached to the curved surfaces of the chords (2,3,4) by timber battens

(9) without further modification to follow those curved surfaces.

Should additional strength be necessary for the assembled truss (1 ), such as in cyclone-prone areas, this additional strength can readily be achieved by using additional laminates in the construction of the chords (2,3,4) and/or by drilling vertically through the chords (2,3,4) and using threaded tie-down bolts

(10) as is known in the art.

Also, additional laminates, either the full length of the respective chords (2,3,4) or of a shorter length sandwiched between two of the full length laminates of the chords (2,3,4), could be incorporated into the structure to provide increased strength where the upper and lower chords converge, This increased strength enables a wider eave to be formed and/or provides more flexibility in the actual positioning of the vertical supports for the overall roof structure, ^'

The present invention thus offers a number of advantages of the prior art, which include:

wider spacing of trusses enabling greater design freedom in the positioning of constructional features such as large bay windows;

standard timber cuts can be used to create a continuous curved structure, both as an outer roof or inner ceiling;

the convergence of the upper and lower chords provides an increased overall strength for the truss which enables (i) wider external eaves tn

be constructed and (ii) provides flexibility in the positioning of the vertical supports for the roof structure for any given span;

total quantity of timber used for a given structure is approximately the same as more conventional triangular timber trusses;

can readily be adapted for use in high stress areas such as cyclone- prone climates; and

provides a curved truss which can be assembled easily from readily available standard components,

It will be appreciated that the above described embodiment is only an exemplification of the various aspects of the present invention and that modifications and alterations can be made thereto without departing from the inventive concept as broadly defined in the following claims,