GB2165278A - A roof covering - Google Patents

Abstract

A roof covering is formed by a heat insulating layer of expanded plastics foam boards 4A, 4B the joints between them being covered by an adhesive strip 5 having a release agent on its upper surface. A membrane 6 formed by a mixture of bitumen and a contact adhesive is applied over the boards 4 and strip 5 to provide waterproofing. If the boards 4 separate due to shrinkage the release agent on the strip 5 allows the membrane 6 to stretch without breaking. <IMAGE>

Description

SPECIFICATION A roof covering This invention relates to a roof covering of the type comprising a heat insulating layer formed by boards of expanded synthetic plastics material placed edge to edge and covered by a waterproof layer of a bitumen based material.

The boards are preferably formed by extrusion to give them smooth upper and lower surfaces.

This type of structure has proved very popular in the past when, to install it, hot bitumen is applied to a roof deck, of concrete, metal, plywood etc., and allowed to cool to about 85"C when it becomes tacky. The polystyrene boards are pressed onto the bitumen so as to hold them in position. A thin glass tissue base felt carrying a soft form of bitumen on its underside is then laid loosely over the polystyrene and hot bitumen is used to bond at least a second layer of felt over that, causing the soft bitumen on the base felt to further soften and stick to the polystyrene.

The second and subsequent layers of roofing felt are made to B. S. 747.

Roofing installed in this way has not withstood the test of time and it has been found that the multi layer waterproofing comprised of roofing felt splits, blisters and subsides. It is the inventor's belief that these widespread problems arise from damage caused to the polystyrene during application of the hot bitumen applied at 1500C-2200C and, in many instances from progressive solar induced heatshrinking of the polystyrene causing the boards to part and causing the roofing felt to split along lines adjacent to where the polystyrene boards abut each other.It will be understood that polystyrene has a heat distortion capability at about 74"C and starts to melt and disintegrate at approximately 80"C, from which it can be seen that to put such a substance into intimate contact with hot bitumen will be bdund to cause damage. It is believed that given a dark surface finish the solar gain temperature at the insulant top surface can attain a temperature of 80"C i.e. in excess of 74"C.

This invention provides a roof covering comprising thermal insulating boards placed edge to edge and made of a material which is subject to shrinkage and a waterproof layer bonded to the sheets and extending across adjoining edges of the boards, characterised by anti-adhesion means inhibiting adhesion between the waterproof layer and border portions of the insulating boards bordering the edges thereof.

By employing an "anti-adhesion means" in this way any stretching of the waterproof layer due to shrinkage of the insulating boards is distributed over a substantial area of the waterproof layer. Splitting of the latter is thus made much less likely. The "anti-adhesion means" can readily be provided by adhesive tape having one adhesive side attached to the insulating boards and an opposite side carrying a silicone or other release agent.

Suitable bitumen based materials are readily available e.g. from HEX'DO (GB) Ltd. of No. 3 Eastern Industrial Estate, Newcraighall Road, Edinburgh under the trade name HEY'DI SK 2000, HEY'DI SK 2000 S and HEY'DI SK 2000 ALU, the former two having a polythene carrier sheet which supports the bituminous substance and the latter having an aluminium carrier sheet which can be an advantage since it serves to reflect solar energy, thereby reducing heat shrinkage to a minimum, and provides fire resistance. Such materials are supplied with a silicone treated release sheet on the side opposite the carrier sheet and it is necessary to remove this.

The bituminous mixture is preferably a mixture containing bitumen and natural or synthetic rubber. The natural or synthetic rubber can be replaced by other substances known for their contact adhesive properties. A suitable non-aggressive solvant could also be included in an adhesive.

One way in which the invention may be performed will now be described with reference to the accompanying drawings in which Figure 1 illustrates a schematic vertical cross-section through part of a roof covering constructed in accordance with the invention; and Figure 2 illustrates a cross-section similar to that of Fig. 1 but illustrating the effect of exposure of the roof covering to solar heat over a period of time.

The roof covering shown in Fig. 1 is applied to a concrete roof deck 1 as follows.

First a primer 2 is preferably applied to the concrete. This can be any one of many suitable products. HEY'DI SK primer is considered particularly suitable and is available from the aforementioned supplier.

Next a cold adhesive 3 is applied, this preferably also being a bitumen, synthetic rubber, solvent base product such as is available, again from for example HEY'DI (G.B.) Ltd..

Their K100 Cold Adhesive, which of thixotropic character is considered particularly suitable since it is not agressive to polystyrene.

Boards, such as shown at 4A and 4B of rigid closed cell expanded and and extruded polysturene foam having smooth continous sealed upper and lower surfaces are then applied, with their edges abutting each other, to form a heat insulating layer. A suitable material for the boards 4 is available under the trade name ROOF MATE from the Dow Chemical Company. A high density expanded bead polyst ene could be used as a second best alternative to extruded foam. This could either be moulded or cut from slab stock, through the latter possibility is not preferred since it tends to produce a dusty friable surface less likely to adhere to a self adhesive membrane 6 now to be described.

A thin paper strip 5 of width about 50 mms to 150 mms (preferably about 75 mms) having a self adhesive layer on one side and a siliconised non-stick layer on the other side is then applied, with its adhesive side down, over the joints between the insulating boards.

A suitable adhesive strip is available from Samuel Jones & Co., St. Neots, Cambridge under the trade name TAKSTRIP.

Having applied the strip 5, a preformed roll of HEY'DI SK 2000, HEY'DI SK 2000S or HEY'DI SK 2000 ALU is unrolled and its siliconised release sheet removed to reveal the adhesive membrane 6. This is pressed onto the surfaces of the boards 4 and over the joints covered by the strip 5. The protective polythene or aluminium carrier sheet 7 for the self adhesive membrane 6 forms the top surface of the roof covering.

Since the membrane 6 adheres by its own contact adhesive properties to the insulating boards 4 no damage occurs to the latter as was the case with a hot application of bitumen applied at a temperature of between 150 C and 220"C or thereabouts and thus the problems of localised disintegration of the polystyrene and subsequent blistering of the weatherproofing can be expected at least to be greatly reduced, and possibly totally eliminated. The use of a flexible cold adhesive below the insulating boards and the underlying surface such as can occur when similar boards are set in partially cooled bitumen as previously described.. The shrinkage of the boards 4 is also tolerated by this construction as is illustrated in Fig. 2.

Referring to Fig. 2 it will be seen that the boards 4A and 4B have diminished in size, more at their upper surfaces than at their lower surfaces since the former are more exposed to radiation from the sun. Substantially less shrinkage normally takes place at the lower portion.

The shrinkage has caused the paper strip 5 to split into parts 5A and 5B in the illustrated case, though in a less severe example of shrinkage the strip may stretch. In either event the silicone release agent on the upper surface of the strip means all of the membrane 6 above the strip stretches in order to provide the necessary waterproof bridge between the upper surfaces of boards 4A and 4B or is not stretched at all. The degree of extension per unit length is significantly less than if the strip 5 were not included. Nevertheless a construction without such a strip may accommodate sufficient shrinkage since the membrane 6 is of plastic consistency so that its upper part can, being supported by the sheet 7, retain its original form whilst alowing the lower part to flow to the left and right with movement of the boards 4.

In the condition shown in Fig. 2 it is to be noted that the upper carrier sheet 7 is held under tension so as to prevent collapse of the waterproof bridge between the boards 4A and 4B. The consistency of the membrane 6 is such that it is not self supporting and cannot retain a condition of tension on its own. Thus it would collapse if not for the presence of the carrier sheet 7.

It is believed that the illustrated technique will solve the problems previously described and create a renewal of the practice of using roof coverings incorporating an extruded polystyrene or moulded polystyrene board. Not only can the aforementioned specific problems be overcome, but the construction as described is particularly resistant to splitting and mechanical damage, the membrane 6 having self-healing properties; and it is furthermore particularly easy to repair, this being possible using a "patch" of the same material as the preformed roll.

Claims (2)

1. A roof covering comprising heat insulating boards placed edge to edge and made of a material which is subject to shrinkage and a waterproof layer bonded to the sheets and extending across adjoining edges of the sheets, characterised by anti-adhesion means inhibiting adhesion between the waterproof layer and border portions of the insulating sheets bordering the edges thereof.

2. A roof covering according to Claim 1 in which the anti-adhesion means is adhesive tape having one adhesive side which is adhered to the insulating sheets and one side carrying a release agent.