GB2233681A - Roof construction - Google Patents

Abstract

The roof construction comprises a number of parallel trusses with cross bracing between. The trusses are made up from top members (10), bottom members (12) and upright members (14) of metal channel secured together. A bracket (22) may be used for supporting cross bracing members (15) and for clamping bottom runners (12) to an existing roof surface. The top members (10) of the trusses describe an inclined surface on which structural insulation boards are mounted, the construction having either inclined top members (10) with horizontal bracing (16) or horizontal top members (10) with inclined bracing (16). The construction is of particular use in overlying an existing flat roof to provide a pitched roof. Structural insulation boards and roofing material overly the construction. <IMAGE>

Description

Roof Construction The present invention relates to roof constructions involving the construction of a framework of trusses with cross bracing.

The construction of a sloping roof surface on an existing flat roof, a technique known as cut-to-fall roofing, is used to provide additional insulation and alleviate drainage problem associated with flat roofing. Settlement of the structure can lead to ponding of rainwater in the settled areas of the roof.

Ponding can, in turn, lead to degradation of the roofing material in the settled areas, resulting in water penetration.

British Standard Code of Practice CP144: Part 3: 1970 Amendment 2527 recaromends that cut-to-fall roofing should have a gradient of not less that 1 in 80. Even at gradients of 1 in 40 (a slope angle of 1.450) settlement and ponding can still occur if the roofing material is not adequately supported.

Presently correction of the fall of settled roofs is achieved using cork, cellular plastic or composite formers. An inclined surface upon which roofing material is subsequently deposited may be built up using two or three standard tapering blocks of cork with flat boards of rigid urethane foam or cork material supporting the tapering blocks of cork to give a graduated incline. The boards are held together and in position by bitumen adhesive, with the desired roof shape being achieved by cutting and stacking of the standard boards.

Such a system does have drawbacks: at roof widths in excess ss of around 6 metres, the volume of insulation material and the cost of installation makes the system uneconomical.

Additionally, in low (thinner) areas of the roof, problems can occur with interstitial condensation.

In accordance with the present invention there is provided a roof construction comprising a nuSber of trusses positioned side by side, each truss being formed fran lengths of metal section and having top and bottom members and a number of upright members therebetween, with further lengths of metal section providing bracing itrdbers between adjacent trusses and the top merabers of the trusses describing an inclined surface on which structural insulation boards and roofing material are supported.

The trusses may have inclined top members and be braced by horizontal lengths of metal section between adjacent trusses.

Alternatively, or in ooobination with this arrangement, the trusses may have horizontal top members increasing in height across the roof with bracing sections between adjacent top members defining the inclined surface.

The trusses may be constructed from lengths of metal section, such as galvanised mild steel channel, either cut to size from stock lengths on site or provided as preformed sections bolted, screwed, welded or rivetted together to simplify construction. The construction may be simplified by use of two sizes of metal channel only: the first being used for the top and bottom members of trusses and the second for the upright members and cross bracing sections. Alternatively a single size of metal channel may be used provided the ends of the upright members and cross bracing section are swaged or crimped.

The present invention further provides a novel bracket by means of which the construction may be further simplified.

The bracket according to the invention preferably has a saddle portion shaped to fit closely around a first member and having one or more sockets to receive the free end of a further member extending transversely to the first member.

Such a bracket may be used in the construction of a framework for a cut-to-fall roof, the saddle portion sitting over the top member of a truss and holding the ends of bracing sections. Where two sections of channel are to be joined end to end, the bracket may be placed over the join and rivetted to each channel section. The bracket may also be used to clamp channel sections to an existing roof surface by means of screws or bolts driven through suitably positioned clearance holes in the sockets and into the roof surface. It will thus be appreciated that the framework may be constructed using a single design of bracket. On metal deck roofs or where fixing centres are random, a modified fining bracket may be used, having a wider fixing point to coincide with the crown of metal deck corrugations.

The use of a number of preformed truss sections and bracing pieces in a framework constructed with the aid of only one or two designs of bracket provides a cut-to-fall roof which is simple to assemble and easily adaptable to different sizes of roof. The completed framework is equivalent to a oonventional truss support and is cheaper to produce and install than, for example, the cork former method described above.

One particular preferred enlxxlunent of the present invention will now be described by way of example only and with reference to the acocoanying drawings in which: Fig. 1 shows a part of the framework at the junction of two truss sections; Fig. 2 shows the bracket used in framework assembly clamping a bottom member to the flat surface; Fig. 3 shows an alternative design of bottom member clamping bracket; Fig. 4 shows the junction of top and bottom members at the lower edge of the framework; Fig. 5 is a side elevation (with exaggerated vertical scale) of an inclined truss constructed in accordance with the present invention; ; Fig. 6 is a schematic plan of a rainwater outlet using the construction of the present invention; and Fig. 7 shows the truss members used in construction of the outlet of Fig. 6.

The framework support for the cut-to-fall roof of the present invention is constructed from mild steel channel as shown in Figure 1.

Truss sections are constructed with the free ends of the upright members 14 inside the channelling of the top mEmber 10 and bottom member 12 and held in position by spot welding or by rivets, bolts or screws through the side walls 18,20 of the channel.

The e bracket 22 used in assembly of the framework is shown in Figures 1 and 2. A rectangular plate 24 with perpendicularly extending side plates 26 defines a saddle portion 28 with internal dimensions corresponding to the external dimensions of the channel used for the top members 10. Flanges 30 extending fram the side plates 26 and end plates 32 define a socket portion 34 having internal dimensions corresponding to the external dimensions of the channel used for the cross-bracing or nogging 16.

A first use of the bracket 22 is shown in Figure 1. A number of parallel trusses are positioned at evenly spaced intervals.

Between the top members 10 of adjacent truss sections, identical flogging portions 16 are provided. The plain (square end) flogging 16 is supported by brackets 22 saddling the top members 10, with all components secured by rivetting, bolting or screwing.

Similar flogging 16, either plain nogging supported by the brackets 22 or mitred nogging secured by rivetting, bolting or screwing is provided between the upright members 14 of adjacent trusses to further strengthen the framework.

A further use of the bracket is shown in Figure 2. The bottom member 12 of a truss is positioned on the surface of an existing flat roof (not shown) and the bracket 22 fitted on top of it. The flanges 30 of the bracket 22 extend across the roof surface and screws passing through clearance holes 35 in the flange 30 and into the roof surface, clamp the bottom members 12 in position.

An alternative design of bottom member fixing bracket 36 is shown in Fig. 3. ffi e bracket is a length of metal channel with slots 37 cut in the side walls of the channel, corresponding in position to the side walls 18 of the bottom member 12. The e bracket 36 has a flunber of clearance holes 38 through which screws 39 or bolts pass to secure the bracket and bottom member 12 to the roof surface.

In the framework of Fig. 1, a bracket 22 is positioned at the junction of a truss top member 10 and an upright member 14 with cross-bracing sections 16 to adjacent trusses.

Structural insulation boards are positioned on the completed framework and screwed directly to the top mebbers 10 and to the cross-bracing section 16. Adjacent boards are butt jointed. The boards, which are laminations of plywood and foam material, are already known and used in the industry for flat roof decking.

Figure 4 illustrates the junction of the top member 10 and bottom member 12 at the lower edge of the framework. The end of the top member 10 is nested in the bottom member 12 which is splayed slightly to allow the fit.

Figure 4 also shows an alternative method of cross-bracing using splayed noggings 16A. The ends of the metal channel are opened out to produce a flat plate 40 which is then bolted or rivetted to the surface of the upper member 10.

One truss shape 42 which may be constructed is shown in Figure 5: the vertical dimensions have been scaled up by a factor of 5 for the sake of clarity. The angled truss 42, with inclined top member 10, is constructed fran a number of preformed sections (42a-g) having bottom members 12a-g of fixed length.

An additional section of different bottom member length may be provided at the upper end of the truss 42 for construction on existing roofs the width of which is not an integer multiple of the truss section bottom member length.

A number of such angled trusses 42 are mounted on an existing flat roof and strengthened by cross-bracing or nogging 16 as described above.

The sections making up each truss 42 are joined by securing adjacent stanchions 14f, 14g together as in Fig. 1.

Additionally, the brackets 22 supporting the cross-bracing 16 are positioned to overlap the joint between adjacent top runners 10f,10g and are rivetted to each.

An alternative design and arrangement of trusses 44 is shown in Figures 6 and 7. In Figure 7, as Figure 5, the vertical dimensions are scaled up by a factor of 5.

The 'square' trusses 44 which have top mebbers 10 and bottom members 12 parallel are provided in a set 44A-H having increasing top/bottom member separation. The nogging between the top members of adjacent trusses is thus inclined at the desired angle of slope and may be plain flogging positioned by means of the saddle brackets shown in Fig. 2 or splayed flogging as shown in Fig. 4. The set of square trusses 44A-H in Figure 7, which are of increasing length as well as height, may be used to construct an inverted pyramid to form a rainwater outlet as in Figure 6 in which rainwater is directed downwardly towards a central drain 46. Sizes for the trusses shown, at 60oIrKn spacing and a slope gradient of 1 in 40, would be: Truss Heist Length Truss Height 44A 21mm 30Orrrn 44E 77mm 4800ttrn 44B 32mm 1200mm 44F 92mn 6000mm 44C 47mn 2400mm 44G 107mn 7200mm 44D 62mm 3600mn 44H 122mm 8400mm The two methods described (inclined trusses with horizontal nogging and horizontal trusses with inclined flogging) may be used separately or in combination to provide a cut-to-fall roof framework in a number of designs allowing roof shapes other than a single slope to be produced.

Claims (14)

Claims

1. A roof construction comprising a number of trusses positioned side by side, each truss being formed fran lengths of metal section and having top and bottom members and a number of upright members therebetween, with further lengths of metal section providing bracing members between adjacent trusses and the top members of the trusses describing an inclined surface on which structural insulation boards and roofing material are supported.

2. A construction according to claim 1, including a bracket having a saddle portion shaped to fit closely around a first member and having one or more sockets to receive the free end of a further member extending transversely to the first member.

3. A construction according to claim 2, in which brackets as defined fit around the top members of adjacent trusses and support bracing members therebetween.

4. A construction according to claim 2 or claim 3, in which brackets as defined fit around the upright members of adjacent trusses and support bracing members therebetween.

5. A construction according to any of claims 2,3 or 4, in which a member extending across a flat surface is attached to the surface by a bracket as defined, which fits around the member, the or each socket being secured to the surface.

6. A construction according to any of claims 2 to 5, in which members, constructed of two or more axially aligned lengths of metal section, are joined together by a bracket as defined, which overlies the joint between adjacent lengths and is secured to each.

7. A construction according to claim 1, in which the trusses are positioned substantially parallel and equally spaced.

8. A construction according to any preceding claim, in which each truss is formed fram lengths of metal channel.

9. A construction according to any preceding claim, in which the top member of each of the trusses is inclined with respect to the bottom member.

10. A construction according to claim 9, in which the bracing members between adjacent trusses are substantially parallel to the plane of the bottom members.

11. A construction according to any of claims 1 to 8, in which the top member of each of the trusses is substantially parallel to the bottom member, the distance between top and bottom member differing between adjacent trusses.

12. A construction according to claim 11, in which all the bracing members between the top members of adjacent trusses are inclined with respect to the plane of the bottom members.

13. A roof construction substantially as hereinbefore described and with reference to the acooNpanying drawings.

14. A bracket for use in a roof construction substantially as hereinbefore described and shown in Figures 1 and 2 of the acoompanying drawings.