GB2089388A - Purlin and insulated roof - Google Patents

Abstract

An inverted channel section purlin (10) has an outwardly directed flange (16A, 16B) along the lower edge of each side. Heat insulating units (34, 36) are assembled around the flanges (16A, 16B), and crosspieces (46) are laid between the purlins with their ends received in recesses (38A) of the units (34, 36). Inner roofing sheets (50) of heat insulating material are laid on the crosspieces. Outer roofing sheets (52) are fixed directly to the top webs of the purlins. <IMAGE>

Description

SPECIFICATION Improvements in or relating to purlins and roof structures This invention relates to a purlin and also to a roof structure in which the purlins are incorporated.

The most commonly used roofing purlin is a Z-purlin. In roofing structures for warehouses, animal houses and like industrial and agricultural buildings often of substantial area, the outer skin of the roof is usually formed by roofing sheets, e.g.

asbestos sheets, which are clamped by means of hook members to the turned back edges of the upper webs of the Z-purlins. At the bottom, the purlins are fixed to the roof stanchions or rafters by means of angle section cleats.

The usual method of locating the hook members in position is by insertion from below through drilled apertures in the purlin and in the roofing sheet, requiring for this purpose that a workman supported on a duckboard above the partially constructed roof should reach downwardly and around the span of the next roofing sheet. This is clearly disadvantageous, more so when overpurlin heat insulation is to be incorporated immediately below the outer roofing sheets, since the seals intended to be effected, at the apertures in said sheets through which the hook members extend, when the roofing sheets are clamped down, are often broken by the load of the workman continuing to work on the roof.

Recently, therefore, there has been an increasing tendency to change to direct fixing, wherein a selftapping screw is passed through the roofing sheet from above and screwed downwardly into the top web of the purlin. With direct fixing, the web with turned back edge conventionally provided at the top of a Z-purlin is no longer required for cooperation with a hook member.

In addition, the conventional Z-purlin is liable to twist, and especially when increased strain is placed on the hook members and purlins due to the provision of heat insulation (which may demand the use of hook members with extra long stems), the entire roof structure can have a tendency to instability.

In our U.K. Patent Applications Nos. 8032387 and 8033274, we have already proposed an improved roofing structure, based on a J-section purlin or on a Z-purlin, wherein the inner roof layer. generally including heat insulation, is arranged between the purlins, combining the advantages of existing over-purlin and existing under-purlin heat insulating arrangements. This improved inter-purlin arrangement, in the case of an insulated roof, requires the use of a heat insulating sleeve, provided around the bottom flange or flanges of the Z-purlin or J-purlin, in order to eliminate the cold bridge which would otherwise exist between the warm interior of the building below the insulation and the cold space above the insulation below the outer roofing skin.

Having regard to the tendency to direct fixing of the outer roofing sheets, it is an object of this invention to provide an improved purlin, less liable to deformation and twist than the Z-purlin, which at the same time facilitates the provision of an inter-purlin heat insulating layer.

According to the invention, there is provided a purlin having a main limb of U-channel section formed by two spaced parellel webs connected at the top by a transverse web to enable direct fixing of outer roofing sheets, and two bottom flanges with turned back edges extending outwardly from the main limb at the bottoms of the respective parallel webs of said main limb.

A preferred purlin has a main limb of length top to bottom between 3 to 5 times the spacing between the parallel webs of said main limb. The overall span of the base of the purlin may be about twice (between 1 2 and 2-21x) the said spacing. The preferred purlin is made of steel, formed by cold rolling.

According to another aspect of the invention, there is provided a heat insulating roofing structure incorporating the above-described purlins. In this structure, a channel-purlin is fixed to a roof stanchion by angle-section cleats one limb of which is received within the purlin channel and clamped therein between a ferrule block and one web of the purlin main limb. This fixing is preferably effected at the ends of the purlin, and the same clamping means is employed to fix in position a U-section jointing sleeve received in the aligned channels of two purlins abutting end to end. On the one side of the purlin channel, the jointing sleeve is clamped directly between the cleat and the purlin web; on the other side the jointing sleeve is clamped directly between the ferrule block and the other purlin web.

The flanges with turned back edges at the bottom of a purlin enable a cold bridge eliminating sleeve of heat insulating material (preferably accommodated in a metal outer sleeve) to be hooked into position, covering the base of the purlin. Tee-bars are laid between the insulated bases of parallel purlins of the roof structure, preferably being located with the aid of locating slots provided in the cold bridge eliminating sleeves. The tee-bars are thus supported on the cold-bridge eliminating sleeves, out of direct contact with the purlins. The purlins and tee-bars together define rectangular trays for supporting a heat insulating layer, suitably held down in the trays.

The interiors of the channels of the purlins above the cold bridge eliminating sleeves will generally be insulated to a lesser extent than the cold space between the purlins above the main heat insulating layer. This can be advantageous in producing a limited warming of the metal of the main limbs of the purlins, thereby reducing condensation problems in the cold space.

A practical example of channel purlin and roof structure in accordance with the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a channel purlin in end view; Figure 2 shows a method of fixing a channel purlin to a roof stanchion or rafter; Figure 3 shows a cold bridge eliminating sleeve hooked on to the base of a channel purlin; Figures 3A and 3B respectively show the outer metal sleeve and insulating filler which form the cold bridge eliminating sleeve; and Figure 4 is a diagrammatic view of a partially constructed roof structure.

Figure 1 shows a channel-section purlin, with relative dimensions (e.g. mm) marked thereon.

The purlin 10 has a main limb of channel section defined by two spaced parallel webs 12A,12B connected at the top by a transverse web 14.

Flanges 16A, 16B with upturned edges 1 8A, 1 8B project oppositely outwards at the bottoms of the webs 12A, 1 2B to define the base of the purlin.

The purlin 10 is formed of cold rolled steel.

Figure 2 shows the manner of fixing a purlin 10 to a stanchion or roof rafter 20. A steel angie cleat 22 has one web suitably fixed to the rafter 20 by means not shown and its other web fixed to the web 12B of the purlin, within the channel thereof, with the aid of a ferrule block 24. The lower part of the ferrule block 24 is readily located by the lower clamping bolt 26, automatically positioning the upper part of the block for insertion of the upper clamping bolt 28. The use of two separate spacers instead of the single block 24 would entail more difficult manipulations. The ferrule block 24 may be moulded or otherwise formed of plastics material. The same clamping bolts 26,28 are used to fix in position a U-shaped jointing sleeve 30 of cold rolled steel bridging the joint between two adjacent purlins 10 abutting end to end.

Figure 3 shows a cold bridge eliminating sleeve 32 located to the base of a purlin 10. As will be clear from Figures 3A and 3B, the sleeve 32 is a composite sleeve consisting of an outer metal sleeve 34 and a heat insulating filler 36.

It is to be noted that the roof structure being formed (see Figure 4) will generally be a pitched roof structure. This is important in relation to Figure 3, as will shortly be made clear, in that the assembly shown in this figure is assumed to form part of a roof structure sloping upwardly to the right.

The outer metal sleeve 36 is formed with upper flanges 42A, 42B having pressed out tabs 38A, 388 (see also Figure 4), which have turned down edges 40A, 40B. The upper flanges of the sleeve 36 in which said tabs are formed are of different widths, so that the tab 38A in the upper flange 42A is not only wider but has a deeper turned down edge 40A. The differing widths of the arms 44A and 44B of the filler 36 are likewise to be noted.The form and dimensions of the component parts 34, 36 of the cold bridge eliminating sleeve 32 are thereby such that it can be hooked over the turned back edge 1 8A of the bottom flange 1 6A of the purlin 10, to be temporarily suspended in such a hooked condition, and then be pushed to the right using the available tolerances and swung upwardly to hook over the turned back edge 1 8B of the flange 1 6B on the other side of the purlin base. It can then be pushed downwardly of the pitch of the roof to transfer the available tolerances back to the left, effectively to fix said cold bridge eliminating sleeve 32 in a permanent position. The sleeve 32 extends along the entire length of the base of a line of purlins with cut-outs to accommodate the fixing cleats 22.

As will be clear from Figure 4, the tabs 38A, 38B define slots enabling the base webs of the tee-bars 46 to be located between adjacent purlins 1 0A, 1 OB with the aid of tee-bar retaining clips 48. The tee-bars 46 are supported on the cold bridge eliminating sleeves 32, out of direct contact with the purl ins 1 0A, OB. Inner roofing slabs 50 of fire-retardant, heat-insulating material are laid into and suitably held down in the rectangularly framed trays formed by the substantially coplanar base webs of the tee-bars 46 and upper flanges 42A, 428 of the sleeves 32.

An adhesive seal can be incorporated around the frames of the trays to create a vapour sealed arrangement.

The outer roofing sheets 52 in Figure 4 are directly fixed to the top webs 1 4 of the purlins 1 0A, 1 or, for example by use of self-tapping screws (not shown).

As previously mentioned, the channel purlin 10 has the advantage of being much less liable to twist and deformation than the conventional Z-purlin, whilst being equally easily produced by cold rolling sheet steel. At the same time, it enables direct fixing of the outer roofing sheets and facilitates provision of an inter-purlin heat insulating arrangement in the manner described with reference to Figures 3 and 4. Additionally, it enables condensation problems to be minimised in the cold space above the heat insulation, while the ferrule block fixing method shown in Figure 2 enables the number of fixing cleats to be reduced as compared to a Z-purlin system.

It should be mentioned that the invention is also applicable to industrial buildings in which, occasionally and in some climates, heat insulation is not required. The tee-bars can then be laid directly between the purlins, located by recesses in the turned back edges of the bottom flanges at the bases of the purlins. Again, the channel purlin described is applicable to over-purlin and underpurlin heat insulating arrangements, although its preferred use is in conjunction with the inter-purlin arrangement also described.

Claims (27)

1. A purlin having a main limb of U-channel section formed by two spaced parallel webs connected at the top by a transverse web to enable direct fixing of outer roofing sheets, and two bottom flanges extending outwardly and oppositely in coplanar relationship from the main limb at the bottoms of the respective parallel webs thereof to assist in the supporting of inner roofing sheets.

2. A purlin according to claim 1, wherein the two bottom flanges have respective edge portions turned back upwardly parallel to the main limb.

3. A purlin according to claim 1 or claim 2, having a main limb of overall depth top to bottom between 3 and 5 times the spacing between the parallel webs of said main limb.

4. A purlin according to claim 3, wherein the overall span of the base of the purlin in the direction normal to its main limb is between 1 2 and 22 times the spacing between the parallel webs of the main limb.

5. A purlin according to claim 4 when appendant to claim 2, wherein the upturned edge portions of the bottom flanges have a depth top to bottom between one eighth and one sixteenth the overall depth of the main limb.

6. A purlin according to any of claims 1 to 5, formed of steel by cold rolling.

7. A purlin/sleeve assembly comprising a purlin according to any of claims 1 to 6, assembled with a sleeve unit which comprises a U-shaped sleeve of heat insulating material inverted to embrace the base of the purlin.

8. A purlin/sleeve assembly according to claim 7, wherein the sleeve unit is constituted by an insulating U-sleeve filler within a metal outer sleeve.

9. A purlin/sleeve assembly according to claim 8 when appendant to claim 2, wherein the metal outer sleeve is generally of U-shape inverted to enclose the inverted U-sleeve filler, said metal sleeve having coplanar inturned edge portions at the tops of its limbs respectively extending over the top edges of upturned edge portions of the bottom flanges of the purlin.

10. A purlin/sleeve assembly according to claim 9, wherein the U-sleeve unit is dimensioned, in the transverse direction normal to the main limb of the purlin, to permit assembly with the base of the purlin by hooking the inturned edge portion of one limb of the outer U-sleeve over the upturned edge portion of the bottom flange on one side of the purlin, and then swinging the sleeve unit upwardly against the bottom of the purlin to enable the inturned edge portion of the other limb of the outer U-sleeve to be engaged over the upturned edge portion of the bottom flange on the other side of the purlin by a displacement of the sleeve unit in the said transverse direction which maintains the hooked engagement on the first mentioned side of the purl in.

11. A purlin/sleeve assembly according to claim 8 or claim 9 or claim 10, wherein the metal outer sleeve is formed along the length of the inturned edge portions of its limbs with spaced locating slots for receiving the ends of crosspieces to be supported perpendicularly to the purlin.

1 2. A purlin/sleeve assembly according to claim 11, wherein the locating slots comprise tabs partially severed from the inturned edge portions and turned inwardly at a lower level than the plane of said inturned edge portions.

13. A purlin/sleeve assembly according to claim 12 when appendant to claim 10, wherein said inturned tabs have downwardly turned edge portions to hook over the upturned edge portions of the bottom flanges of the purlin.

14. A roof structure comprising a plurality of purlins according to any of claims 1 to 6, mounted to the roof stanchions in spaced parallel arrangement, a plurality of crosspieces in the form of inverted tee-bars supported in spaced parallel arrangement between the purlins on the bottom flanges of the latter, thereby to define rectangularly framed trays, and inner roofing sheets supported in said trays.

1 5. A roof structure according to claim 14, wherein each purlin is fixed to a roof stanchion by angle-section cleats one limb of which is received in the channel defined by the spaced parallel webs of the main limb of the purlin, said limb of the cleat being clamped in said channel between a ferrule block and one of said parallel webs.

16. A roof structure according to claim 1 5, wherein the ends of the purlin are fixed to the roof stanchion, and the clamping means associated with the ferrule block is also employed to fix in position an inverted U-section jointing sleeve received in aligned channels of two purlins abutting end to end.

1 7. A roof structure according to claim 16, wherein, on one side of the purlin channel, one web of the U-section jointing sleeve is clamped directly between the cleat and the one web of the main limb of the purlin and, on the other side of the purlin channel, the other web of the U-section jointing sleeve is clamped directly between the ferrule block and the other web of said purlin main limb.

18. A roof structure according to any of claims 14 to 17, having outer roofing sheets directly fixed to the top flanges of the purlins.

19. A heat insulating roof structure comprising a plurality of purlin/sleeve assemblies according to any of claims 7 to 1 3 mounted to the roof stanchions in spaced parallel arrangement, a plurality of crosspieces in the form of inverted teebars supported in spaced parallel arrangement between the purlins on the top surfaces of the sleeves which embrace the bottom flanges of the purlins, thereby to define rectangularly framed trays, and heat insulating sheets supported in said trays.

20. A roof structure according to claim 19, wherein each purlin is fixed to a roof stanchion by angle-section cleats one limb of which is received in the channel defined by the spaced parallel webs of the main limb of the purlin, said limb of the cleat being clamped in said channel between a ferrule block and one of said parallel webs.

21. A roof structure according to claim 20, wherein the ends of the purlin are fixed to the roof stanchion, and the clamping means associated with the ferrule block is also employed to fix in position an inverted U-section jointing sleeve received in aligned channels of two purlins abutting end to end.

22. A roof structure according to claim 21, wherein, on one side of the purlin channel, one web of the U-section jointing sleeve is clamped directly between the cleat and the one web of the main limb of the purlin and, on the other side of the purlin channel, the other web of the U-section jointing sleeve is clamped directly between the ferrule block and the other web of said purlin main limb.

23. A roof structure according to claim 22, having outer roofing sheets directly fixed to the top flanges of the purlins.

24. A roof structure according to any of claims 19 to 23 when appendant to claim 11, wherein the ends of the inverted tee-bars are held down in the locating slots in the outer sleeves of the sleeve units by retaining clips which engage beneath the inturned edge portions of the limbs of the outer sleeve at the sides of said locating slots.

25. A purlin substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

26. A purlin/sleeve assembly substantially as hereinbefore described with reference to Figures 3, 3A and 3B of the accompanying drawings.

27. A roof structure substantially as hereinbefore described with reference to Figures 2 and 4 of the accompanying drawings.