GB2261229A - Insulating roofing - Google Patents

Abstract

A roofing structure especially for tropical climates in which it provides good heat insulation comprises a plurality of roofing panels 1 each comprising a lightweight insulating core 8, for example of high density expanded polystyrene, and a rigid, self-supporting coating 9, for example of glass-reinforced cement, around the core, the panels being disposed in edge- to-edge abutment and being spaced from (4) and supported on a substantially water-impermeable roofing surface 5, 6, 7. <IMAGE>

Description

IMPROVEMENTS RELATING TO ROOFING SYSTEMS This invention relates to roofing systems and is particularly concerned with insulating roofing systems.

In tropical climatic conditions, buildings require some form of insulation against heat from the sun. The conventional flat reinforced concrete roofs of commercial, industrial and to a certain extent residential buildings are subject to maximum exposure as they sit on a horizontal plane. In certain countries, building plans are subject to guidelines and regulations imposed by the authorities and the thermal transmittance of roofs has to meet required values as dictated by the authorities. Therefore some kind of insulation material will have to be incorporated into the roofing design in order to comply with the requirements. In the selection of a proper insulation material, its compatibility with the substrate, the water-proofing membrane and the function of the roof itself must be considered.Due partly to the limited availability of suitable insulation materials for the roof, it is difficult to strike a balance between on the one hand, good thermal insulation properties, resistance to wear and lightweight and on the other hand water-proofness, cost-effectiveness and ease of application.

In accordance with the invention, there is now provided a roofing structure including a plurality of roofing panels each comprising a lightweight insulating core and a rigid, self-supporting coating around the core, the panels being disposed in edge-toedge abutment and being spaced from and supported on a substantially water-impermeable roofing surface.

The roofing panels used according to the invention are preferably manufactured from materials which find wide use in the construction industry and whose properties and characteristics are already well documented. For example, the lightweight insulating core is preferably of high density expanded polystyrene which finds wide use throughout the construction industry as an insulating material and is already manufactured in large quantities and is therefore relatively low in cost. Alternatively, the lightweight insulating core may be of other foamed or expanded plastics materials, such as foamed polyurethane, or of glass or mineral fibres, if necessary suitably treated to render them selfsupporting. Similarly, the coating around the core can be of a wide variety of structural materials but is preferably of a cementitious nature, for example glass-reinforced cement.Alternatively, it can be of plastics materials, especially fibre reinforced plastics materials.

The panels may be of any convenient shape or size to achieve their purpose and to enable their safe and rapid transport and manoeuvrability on site. For example, the panels may be of rectangular or hexagonal shape, but are preferably rectangular. In use, the panels are disposed on a water-proofing finish on the structural roof surface to form a continuous roofing surface, but are spaced from the water-proofing finish to permit rainwater which will percolate between the panels, to run off. Such spacing may be from 2 to 10 mm but is preferably approximately 5 mm, and may be achieved by arranging the corners of rectangular panels, for example, on suitable spacers. This arrangement has the additional advantage of maintaining the under-surface of the panels out of contact with the water-proofing finish to prevent rupture of the latter.

The roofing system of this invention can be considered to be an adaptation of the inverted roof system in that the insulation layer is situated above the water-proofing membrance to offer protection against U-V and weathering exposure. The significant difference is that thermal insulation is provided for example in a preferred and especially straightforward embodiment of the invention, by expanded high-density polystyrene foams encased all round with a skin of glass reinforced cement in the form of a lightweight panel. The panels are placed directly over the waterproofing membrance with a slight clearance of about 5 mm for example, to allow drainage of surface run-offs, resting on padded footings on four corners of the panels to cushion their weight and prevent puncture of the membrance.Depending on the thickness of the structural roof slab, the thickness of the insulating panels may be varied during factory production to ensure compliance with the existing thermal transmittance value requirement. The versatility of the glass reinforced concrete skin offers a wide variety of finishes including moulded patterns and the usage of colour pigments to create an aesthetic appeal over the entire roof.

In general, the advantages of the insulating panels outweigh those associated with conventional roofing systems and may be summarised as follows: (a) Thermal insulation value With the core made of expanded polystyrene foam, the insulation value of the panels ranks among the best when the weight factor is considered.

Expanded polystyrene of density 16 kg/m3 has a K-value (thermal conductivity - W/m deg K) of 0.035 compared to vermiculite plastering of density 640 kg/m3 at K-value of 0.202 and concrete of density 2400 kg/m3 and K-value of 1.442.

(b) Compatibilitv with substrate-water-proofinq membrance As the panels are pre-casted and placed on site, the problem of compatibility with either the substrate or the water-proofing layer is totally avoided. In conventional roofing systems in which the insulation layer is cast on site directly on top of the substrate or the membrance, differential stressing at the interface of the layers can cause cracks to occur resulting in delamination of the insulation from the base.

(c) Water absorption and retention Conventional warm-roof systems require the water proofing membrance to be laid over the insulation layer; this is a common system adopted widely in practice in tropical countries. The insulation materials specified for such systems are usually lightweight screeds of either vermiculite cement or air-entrained concrete. Being cast in-situ and being cementitious in nature, the screed normally requires a curing period of 14 days. In tropical climatic conditions, heavy showers of rain can occur throughout the year and the exposed insulation screed may be saturated during a downpour.Due to the absorption and retention of such moisture by exfoliated vermiculite or the entrapment of moisture within the pores of air- entrained screed, the drying out period may be excessively prolonged and if the water-proofing membrance is to be laid over the insulation screed before it has completely dried, problems with blistering of the membrane occur with damaging results. With the insulating panels of the invention, the polystyrene core is protected by the GRC skin which because of its density will exclude most of the moisture. As pre-cast panels, curing occurs in the factory thus saving time on the construction site. In this system, the membrance will be laid directly over cast reinforced concrete and due to the much higher density of the concrete, water absorption if any is kept to a minimum.

(d) Protection of water-proofing membrane As in the inverted roofing system, with the insulation placed above the water-proofing membrane, the surface temperature of the membrane will be kept fairly constant since the insulating panels will act as a thermal screen. This will in turn minimise damage to the membrane due to cyclic thermal stressing. The panels also protect the membrane against damaging U-V radiation and surface erosion by wind and rainwater and therefore a lower performance (and less costly) water-proofing membrane may be used.

(e) Trafficability The GRC skin on the insulating panels is sufficiently thick to resist all forms of foot traffic and also includes limited wheel-based traffic such as pallet-trucks and wheelbarrows, for example. The panels are also suitable for use in roof-gardens and car-park decks subject to filing the area first with a layer of sand before placement of the panels. It should be noted that the water-proofing membrane must be able to resist ponding when used in the above situations.

(f) Aesthetic finishing The insulating panels may be moulded and coloured to form decorative patterns to improve the aesthetic finish of the roofs. Due to the versatility of the GRC encasement, the finish may be in the form of tiles, ceramics or granolithic without the common problems of such tiles without the common problems of such tiles delaminating in the conventional case-in-situ screeding method because of differential thermal movement of the substrate.

(g) Maintenance of roof Since the panels are relatively light and can be lifted up quite easily, the water-proofing membrane may be inspected and any damages repaired without great difficulty.

The invention will now be described in greater detail by way of example only with reference to the accompanying drawings, in which: Figs. l(a), l(b) and l(c) are top, bottom and side views of a roofing panel; and Fig. 2 is a cutaway perspective view of a roofing system according to the invention.

Referring first to Figs. l(a), l(b) and l(c) of the drawings, there is shown a roofing panel generally designated 1. The panel shown is in the form of a 600 mm square slab having a thickness of approximately 40 mm. Its top surface 2 has been formed to represent a tiled finish. Its bottom surface 3 is provided with pads 4 of synthetic rubber material at each corner, which serve to support the panel on a roof surface.

A roofing system according to the invention is shown in Fig. 2. It comprises a reinforced concrete roof slab 5 some 150 mm thick which supports a 50 mm sand/cement screed 6 applied to give a slight fall to provide water run-off. On the screed 6 there is a water-proof membrane 7 which may be a plastics sheet or, preferably, a liquid-applied material which has been allowed to dry and cure. It is on to this waterproof membrane 7 that the insulating panels 1 have been applied, standing on the pads 4. As can be seen in Fig. 2, the panel itself consists of a core 8 of 25 mm expanded polystyrene foam coated on both sides and on all edges with a 7 mm thick skin layer 9 of glassreinforced cement.

In the arrangement depicted in Fig. 2, the complete roof structure will have a thermal conductivity of approximately 0.85 W/mOK.

The following technical specifications apply to the major components of the insulating panels, namely the GRC skin and the expanded polystyrene foam core.

Due to the versatility of the GRC, the specifications can be adjusted to suit the overall requirement of the finished product in line with its intended usage, i.e.

for heavy traffic roofs the glass fibre contents may be increased to give better tensile strength.

1. GRC specifications (a) Cement Ordinary Portland cement (OPC) to BS 12.

(b) Sand Fine clean river sand free of excessive silt of particle size in the range of 150 pm to 1 mm.

(c) Glass Fibres Alkali-resistant (AR) glass fibres for example those supplied under the trade name Cem-FIL which are pre-cut chopped strands of 12 to 25 mm length.

(d) Matrix ratio Aggregate/cement ratio - 0.25 or more Glass fibre ratio - 3% to 6% by weight Modified by suitable acrylic polymers for workability and improved strength.

(e) Density Dry density approximately 1800 to 2000 kg/m3.

(f) Thermal conductivity "K" value - 0.3 W/m deg K (g) Method of placement Using pre-mix method with chopped fibres incorporated in the fluid matrix and mixing at low-shear to distribute the fibres in all directions to produce a random three dimensional orientation of the fibres in the composite.

2. Expanded Polystyrene Foams (a) Density Ranging from 16 kg/m3 to 32 kg/m3 depending on usage of roof.

(b) Compressive strength Approximately 50 KN/m2 to 250 KN/m2 (c) Thermal conductivity K value - 0.028 to 0.035 W/m deg K (d) Grade Self-extinguishing expanded polystyrene EPS to BASF F 321/F 412.

3. Desiqn of panels 1. Suitable dimensions are as follows: (a) Lengths Available either as 600 mm x 600 mm or 750 mm x 750 mm.

(b) Thickness of core (EPS) Minimum thickness of 25 mm. Increment in 5 mm up to 40 mm depending on insulation value to be achieved.

(c) Thickness of GRC skin All round thickness to be minimum 7 mm thick and may be extended to 12 mm for heavy loading requirement or special finishing, e.g. granolithic trowel finishing.

(d) Available decorative finishing The versatility of the GRC skin offers a wide variety of decorative finishing to be incorporated into the design of the panels and colour pigmentation may be added to enhance the effect. Ceramic or mosaic tiles may be trowelled onto the panels during fabrication, thus saving time and ensuring quality control at manufacturing standard when compared to site application.

The panels will generally be manufactured by the pre-mix method whereby the pre-cut chopped strands of glass fibres will be mixed into the cement/sand fluid matrix and poured into a vibrating mould to form the required shape and thickness. Normal curing or accelerated steam curing may then be carried out.

Polymer modification with an acrylic resin may be part of the mix to improve its theology Standard quality checks on the panels will be based on the normal testing of GRC including hardness/impact and tensile breaking tests.

The insulating panels used according to the invention offer many advantages over the components of conventional roofing systems, in particular savings both in terms of time and money. The roofing system incorporates a protective layer together with a thermal insulation core to be installed over the screed/reinforced concrete substrate in a simple onestep installation without any cumbersome "wet works" on site.

Claims (7)

CLAIMS:

1. A roofing structure including a plurality of roofing panels each comprising a lightweight insulating core and a rigid, self-supporting coating around the core, the panels being disposed in edge-toedge abutment and being spaced from and supported on a substantially water-impermeable roofing surface.

2. A structure according to claim 1, wherein the cores of the panels are of high density expanded polystyrene.

3. A structure according to claim 1 or claim 2, wherein the coating around the cores of the panels is of glass-reinforced cement.

4. A structure according to any one of claims 1 to 3, wherein the panels are rectangular.

5. A structure according to any one of claims 1 to 3, wherein the panels are hexagonal.

6. A structure according to any one of claims 1 to 5, wherein the panels are supported at their corners on spacing members which are supported on the roofing surface.

7. A roofing structure according to claim 1, substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.