GB2205873A - Flat roofing - Google Patents

Abstract

Flat roofing material comprises a waterproof sheet (7) partially bounded to a layer of foamed material (5) by penetration of the foamed material (5) through apertures (9) in a perforated sheet (6) disposed between the waterproof sheet (7) and the foamed material (5). The waterproof sheet has a vapour permeable material bonded to one surface. <IMAGE>

Description

FLAT ROOFING This invention relates to flat roofing.

Provision of means for dissipation and venting of water or other vapour from beneath the waterproof covering (weathering) of flat roofing is an important feature in the design of such roofing.

Omission of means for dissipation and venting may result in blistering in hot weather, due to expansion of vapours and gases collected or trapped underneath the waterproof layer.

Partial bonding of the first layer is commonly employed in construction of built-up felt weathering to provide a release zone for trapped vapour and gases.

Partial bonding also allows for differential movement between the layers of felt and the insulation. A common method of partial bonding is to lay a sheet of perforated gritted felt upon the insulation material, the gritted surface facing downwards. Application of molten bitumen followed by a layer of felt, causes the latter to bond to the insulation through the apertures in the perforated sheet.

According to the present invention, flat roofing material comprises a waterproof sheet partially bonded to a layer of foamed material by penetration of the foamed material through apertures in a perforated sheet disposed between the waterproof sheet and the foamed material.

The waterproof sheet may comprise gritted bitumenous felt, or other sheet material having granular, fibrous or other material through which vapours or gases may permeate bonded to one surface. The perforated sheet may comprise a glass fibre sheet, or other dimensionally stable material which will bond to and stablise or reinforce the insulation, but remain non-adherent to bitumen which may be present in the waterproof sheet.

Roofing materials in accordance with this invention may be conveniently manufactured by application of the perforated and waterproof sheets to the foaming material prior to curing of the latter, causing direct bonding of the foamed material to the waterproof sheet.

Manufacture of the roofing material in the factory rather than in situ confers several advantages over the prior art. Application of molten bitumen in the prior art method is not amenable to precise control. The temperature and viscosity of the bitumen may vary, dependent on weather conditions, distance of the site of application from the source of molten bitumen, rate of application and many other factors. The extent of lateral penetration of the bitumen between the perforated sheet and the insulation layer is dependent on the viscosity of the bitumen and the degree of separation between the perforated sheet and the insulation, making the degree of bonding (which is impossible to observe) very difficult to control.Furthermore, application in or immediately following rainy weather may result in the occlusion of an unacceptably high amount of water between the roofing layers and poor bonding strength. Moreover, bitumen if used to partially bond the waterproof layer to the insulation, may soften or melt when additional layers of felt and hot bitumen are applied to the waterproof layer.

The invention is further described by means of example and not in any limitative sense, with reference to the accompanying drawings, of which Figure 1, is a diagramatic illustration of the prior art; Figure 2 shows the laying of a roof in accordance with the prior art; Figure 3 is a diagrammatic illustration of the construction of roofing in accordance with this invention; Figure 4 is an enlarged partial cross section of roofing in accordance with this invention and Figure 5 illustrates one method of manufacture of roofing material in accordance with this invention.

Figure 1 illustrates one formation of conventional built up flat roofing. Insulation boards (1) composed of foamed polyurethane, polyisocyanurate, phenolic or other insulation material, are fixed on the roof deck, vapour control layer, or other surface (not shown). Sheets (2) of apertured material, such as BS 747 type 3G perforated gritted felt, are laid grit side down upon the boards (1) and molten bonding bitumen (not shown) is poured on to it.

The molten bitumen which passes through the apertures spreads laterally through the layer of aggregate (grit), increasing the bonded area. The extent of lateral spreading is dependent upon the size of the aggregate (grit) and bitumen temperature, and other factors, but apertures having an area of approximately 8% of the total area have been found to afford approximately 12-30% bonded area.

Sheets (3) of felt, e.g. BS 747 type 3B, are unrolled into the molten bitumen as shown in Figure 2. A covering layer of bitumen, bitumen polymer or pitch polymer felt cap sheets (4) may form the external surface of the roof.

Figures 3 and 4 illustrate the construction of roofing material in accordance with this invention. A layer of foamed polymer plastics material (5) is allowed to expand through apertures {9) in a perforated sheet (6) into engagement with a waterproof sheet (7). Curing of the foamed polymer (5) causes it to bond to the sheet (7) in the vicinity of the apertures (9).

The sheet (6) may be composed of glass fibre or a like material, which is non-adherent to the sheet (7).

Wet-laid or other glass fibre sheeting may be coated, except in the vicinity of the perforations, to impede both the passage of foaming insulation material and adhesion to the sheet (7). Suitable coatings include polyethylene, polypropylene or other polymers, metal foils, etc.

Alternatively, perforated gritted felt, similar to BS 747 type 3G, may be employed as the sheet (6), the gritted surface being directed upwards towards the waterproof layer.

When glass fibre sheeting, bitumen felt, or other sheeting (7) is employed, the partially bonded area generally corresponds to the area of the perforations.

Thus, perforations occupying 12-30% of the total area are preferred in this case.

The foamed layer may be of any convenient thickness and density. Thicknesses of 20-100mm may be suitable, although thicknesses up to 150mm may be employed. Foam densities of 32-40 kgm-3, or others known to those skilled in the art, may be conveniently employed.

Wet-laid, glass fibre tissue having a weight of 35-120 gum~2 (estimated as the unperforated material) has been found to be suitable as the sheet (6). This may be coated on the upper side adjacent to the sheet (7) with a polymer (or metal foils, etc) of appropriate melting point to resist melting under the temperatures of manufacture of the insulation board or of those temperatures transmitted to the coating during weathering of the roof with hot bitumen. Where a polymer coating is employed, a coating weight of 25- 70gm- 2 may be applied.

The waterproof sheet (7) may comprise a bitumenous felt of a type commonly used for roof weathering, or any other sheeting known or found to be compatible with bitumen roofing, with aggregate (8) bonded to the side adjacent to the perforated sheet (6). The aggregate may be of any type and size commonly used in the manufacture of roofing felts, but sand of size 16/30 mesh has been successfully employed for this material. In an alternative version the aggregate is replaced by a layer of fibrous material such as polyester, glass fibre or other strong, stable, rot proof material.

The layer of aggregate or fibrous material may be bonded to the sheet (7) by means of bitumen, polymer modified bitumen, or other substances compatible with the sheet (7) and with the foamed insulation material.

Fine aggregate such as sand, limestone, talc, mica, or other material, or combination of materials, of approximately 150 mesh size, may be bonded to the exposed upper surface of the sheet (7) to reduce the risk of stored boards sticking together.

The lower face of the insulation panel (to be fixed to the vapour control layer or roof deck) may comprise a sheet (10) of glass fibre tissue, impregnated or treated glass fibre tissue,bitumen coated glass fibre tissue, metal foil, or a combination thereof, or any other durable stable sheeting commonly used as a facing material in the manufacture of insulation boards for roofing purposes.

In alternative embodiments of the invention, the aggregate (or alternative fibrous layer), may be bonded to the upper face of the perforated sheet (6) rather than the lower face of the waterproof sheet (7).

In alternative embodiments of the invention, the sheet (7) may be waterproof or otherwise, but may be resistant to penetration by (and be capable of forming secure attachment to) bonding bitumens or other adhesives commonly used in roof weathering applications.

Use of roofing material in accordance with this invention not only allows good control during manufacture, but also facilitates installation, particularly in wet weather. Weathering by bonding subsequent layers of felt in hot bitumen is easier and quicker than in the prior art, as there is no longer a requirement to ensure that molten bitumen flows into all of the perforations in the 3G felt. A strippable water resistant covering sheet may be provided to keep the upper surface of the sheet (7) dry prior to installation.

Gases may be gradually evolved from foamed insulation materials, due to partial hydrolysis or the diffusion of blowing agent through ageing. Water vapour may also pass through the insulating material, due to high internal vapour pressures in the building beneath.

This invention provides means for dissipating and venting such gases and vapours. In addition, the air layer retained by the partial bond enhances the thermal insulation properties of the roofing material and reduces the risk of damage to the foamed insulation layer by hot bitumen.

Bonding of the perforated and waterproof layers to the foamed material enhances the mechanical strength and stability of the latter.

In use, the insulating panels are attached to the roof deck or vapour control layer by conventional means, usually employing hot bitumen or other specialised adhesives, and then weathered with normally two layers of bitumenous felts, each of which is bonded in hot bitumen or by other means appropriate to the type of felt employed.

Figure 5 illustrates manufacture of roofing boards in accordance with this invention.

Sheets (26, (27) and (30) are conveniently provided in the form of rolls of material, for ease of handling.

Sheet (30) is unrolled and passed through mechanisms which tension and guide the sheet.

Foaming prepolymer (25) is applied to the sheet (30) by spraying or by any other convenient method known to those skilled in the art.

Where the sheet (30) comprises a glass tissue or other fibrous material, coated or laminated on one face with another material such as bitumen, metal foil, etc. the foaming prepolymer is normally applied to the uncoated side.

Sheets (26) and (27) are each unrolled and separately tensioned and guided in a similar manner to that of sheet (30).

Sheet (26) is then applied to the rising foam (25), before the latter is cured, causing the sheet (26) to be bonded to the foam.

Where the sheet (26) comprises glass tissue or other fibrous material, coated or laminated on one face with another material such as polyethylene, polypropylene, or other polymer, metal foil, etc., the uncoated side is normally applied to the rising foam.

Sheet (27) is then applied to the top sheet (26) before the rising foam (25) is cured, causing the foam which penetrates the apertures in the sheet (26) to impregnate and adhere to the lower face of the sheet (27).

The composite material is then passed into a suitable conveyor mechanism, which holds the composite together until the foam (25) is sufficiently cured, and thence to a sawing process which reduces the composite to insulation panels of convenient size.

In an alternative method of manufacture sheets (26) and (27) are each unrolled and separately tensioned and guided.

Sheet (26) is then laid on top of sheet (27) and foam (25) is applied to the top of sheet (26) (uncoated side). A proportion of the foam penetrates the apertures (9) in the sheet (26) and adheres to the sheet (27). When this alternative method of manufacture is employed, foaming prepolymer (or foam) (25) spreads laterally to some extent between the bottom surface of the sheet (26) and the top surface of sheet (27). In this instance, the apertures (9) in the sheet (26) may be reduced in size to achieve the desired 12-30% total bonded area. Sheet (30) is then applied to the top of the rising foam (25) before the latter has cured. (Foam to the uncoated side) then composite passed into conveyor, cured and sawn to convenient sizes.

Claims (10)

1. Flat roofing material comprising a waterproof sheet partially bonded to a layer of foamed material by penetration of the foamed material through apertures in a perforated sheet disposed between the waterproof sheet and the foamed material.

2. Flat roofing material as claimed in claim 1, wherein the waterproof sheet comprises a sheet material having a vapour permeable material bonded to one surface.

3. Flat roofing material as claimed in claim 2, wherein the waterproof sheet comprises gritted bitumenous felt.

4. Flat roofing material as claimed in any preceding claim, wherein the perforated sheet comprises a glass fibre sheet.

5. Flat roofing material as claimed in any preceding claim wherein the perforations occupy 12% to 30% of the area of the perforated sheet.

6. Flat roofing material as claimed in claim 4, wherein the glass fibre sheet comprises wet-laid glass fibre tissue having a weight when unperforated of 35 to 120gum

7. Flat roofing material as claimed in claim 6, wherein the glass fibre tissue is coated on the upper side with 25 to 70gm 2 of a polymer coating.

8. Flat roofing as claimed in claim 1 or 2, wherein the perforated sheet has a layer of aggregate bonded thereto.

9. Flat roofing substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings.

10. A method of manufacture of flat roofing as claimed in claim 1, substantially as hereinbefore described with reference to Figure 5 of the accompanying drawings.