GB2379707A

GB2379707A - Transparent roofing panel

Info

Publication number: GB2379707A
Application number: GB0218628A
Authority: GB
Inventors: Thomas Gordon Ogilvie
Original assignee: HARTINGTON CONWAY Ltd
Current assignee: HARTINGTON CONWAY Ltd
Priority date: 2001-09-17
Filing date: 2002-08-12
Publication date: 2003-03-19
Anticipated expiration: 2022-08-12
Also published as: GB2379707B; GB0122388D0; GB0218628D0

Abstract

A transparent roofing panel comprises rigid upper and lower layers 2, 22 which are attached to each other along their longitudinal edges 4, 8, 26, 28 and spaced from each other between their longitudinal edges to form a void. A flexible membrane 18 is stretched across the void. Split fillers in upper 12 and lower 20 parts may be provided between the upper 2 and lower 22 layers running transversely and spaced at intervals in the longitudinal direction. The membrane may be held between the upper 12 and lower 20 parts of the split fillers. A method of manufacturing the roofing panel is also described.

Description

TITLE Rooflights DESCRIPTION Technical field The invention relates to the field of rooflights and in particular to rooflights having multiple skins for effective heat insulation.

Background A typical pitched roof of an industrial building comprises an inner liner panel and outer sheeting of metal, fibre-cement or plastic. The space between the liner panel and the outer sheeting is filled with insulation to reduce the escape of heat from the building through the roof. To admit daylight to the building, rooflights must be built into the roof. A basic double-skin rooflight comprises generally rigid, mutually spaced, translucent upper and lower layers corresponding to the liner and outer sheeting of the roof. Typically, they are made of glass-reinforced plastic (GRP) or polycarbonate. However, because it is not possible to stuff the void between the inner and outer layers with insulation without also blocking the light, such rooflights are a major source of heat loss from the building, typically with a heat flow per unit area of about ten times that of the insulated roof.

The rate of heat loss through a roof or rooflight is given as a U-value in units of watts per square metre per degree Celsius (Wm-2 per C). Current U. K. building regulations allow up to 20% of a roofs area to be occupied by rooflights, provided that the rooflights have a U-value of no more than 3.3 Wm' per C. New regulations expected in 2002 will reduce that figure to 2.2 Wm-2 per C.

Each layer or"skin"of a rooflight presents a pair of phase barriers (air-to-solid and solid-to-air) that hinder the transport of heat through the rooflight. A typical U-value for a single-skin rooflight is 5.6 Wm-2 per C, for a double-skin it is 2.8 Wm-2 per C and for a triple-skin 1.8 Wm' per C. Thus it is desirable to increase the number of skins across a rooflight and at least three skins are likely to be needed to comply with

the new building regulations. Of course, it is also desirable that the additional skins should not add excessively to the cost or weight of the rooflight and not adversely affect its performance in admitting light to the building and excluding moisture.

Existing triple-skin rooflights comprise three rigid, mutually spaced layers, which are either extruded from polycarbonate or bonded together from GRP. To add further layers in this way adds to the expense and weight of the rooflight, while cutting down the transmission of light. Furthermore, the points at which successive layers are bonded together provide"bridges"for the flow of heat, reducing the insulation efficiency of the rooflight.

Summary of the invention The invention provides a rooflight comprising: a substantially rigid upper layer and a substantially rigid lower layer, each of the upper and lower layers having opposing longitudinal edges, the upper and lower layers being attached to each other along the longitudinal edges and spaced from each other between the longitudinal edges to form a void; and a flexible membrane stretched across the void between the upper and lower layers.

The flexible membrane provides a lightweight and cheap solution to the problem of providing an extra skin in the rooflight. Because the membrane is stretched across the void, it is self-supporting and there is no need to bond the skins together at intermediate points that would increase heat loss.

It should be noted that, in this specification, the terms"upper"and"lower"are used merely to distinguish the layers and do not necessarily indicate the orientation of the rooflight during use or manufacture. Indeed, the preferred method of manufacture of the rooflight involves inverting it between certain steps.

The membrane needs to be held in place, first because it is under tension and second to seal the two parts of the void on respective sides of the membrane from one another

and prevent air from circulating between them. In the rooflight according to the invention, the membrane may be clamped between the upper and lower layers along at least one of the longitudinal edges, which allows the rooflight to be manufactured simply, without careful positioning of the membrane. Alternatively, the membrane may be adhered to the upper or lower layer adjacent to at least one of the longitudinal edges, which requires more careful positioning of the edge of the membrane but allows the edges of the upper and lower layers to be in direct contact with each other, which may assist adhesion between them. The membrane may also be adhered to a longitudinal strip fixed to the upper or lower layer.

In a preferred embodiment of the invention, the upper and lower layers are generally planar; the attachment between the upper and lower layers at one of the longitudinal edges is generally in the plane of the upper layer; and the attachment between the upper and lower layers at the other of the longitudinal edges is generally in the plane of the lower layer; whereby the membrane is stretched diagonally across the void.

The rooflight according to the invention preferably further comprises narrow fillers that extend transversely across the void, the fillers being spaced at intervals in the longitudinal direction; wherein each filler comprises an upper part and a lower part, with the membrane being clamped between the upper part and the lower part. This helps to locate the membrane within the void and to define its shape and tension.

The invention previously described can readily be adapted to comprise a plurality of the flexible membranes stretched across the void between the upper and lower layers and spaced from one another; optionally being clamped between fillers that are divided into the requisite number of parts.

Preferred materials are polyester for the membrane and glass-reinforced plastic for the upper and lower layers.

The invention further provides a method of manufacturing a rooflight, comprising the steps of :

(a) providing a substantially rigid lower layer having opposing longitudinal edges; (b) laying a flexible membrane across the lower layer from one longitudinal edge to the other; (c) laying a substantially rigid upper layer over the lower layer and the flexible membrane; and (d) attaching the upper layer to the lower layer along their respective longitudinal edges to form a void between the upper and lower layers, with the flexible membrane being stretched across the void.

Between steps (a) and (b), a plurality of lower parts of narrow fillers may be

"cs ; ; ^"/4 svev ly across I^w lwy-ei-vaIs +I'positioned transversely across the lower layer at intervals in the longitudinal direction, the corresponding upper parts of the fillers being positioned above the lower parts between steps (b) and (c) so as to clamp the membrane between the respective upper and lower parts of the fillers.

The drawings Figures 1 to 7 show successive steps in the manufacture of a rooflight in accordance with the invention, all viewed in transverse section; and Figures 8 to 11 show alternative ways of fixing the flexible membrane of a rooflight in accordance with the invention, all viewed in transverse section.

Figure 1 shows the lower layer 2 of a rooflight, which is translucent and substantially rigid. In this embodiment of the invention, the lower layer is manufactured from thermoformed GRP. Near one longitudinal edge 4 of the lower layer 2, at the left side as viewed in the drawing, is a small, upwardly projecting rib 6. The other longitudinal edge 8, at the right side as viewed in the drawing, is on a relatively tall, upwardly projecting leg 10.

The next step in manufacturing the rooflight is shown in Figure 2. The lower parts 12 of narrow, split fillers are positioned at intervals along the length of the lower layer 2.

The fillers are preferably of a foam material and approximately 25-50mm in width.

The lower surface of the filler part 12 is shaped to match the profile of the lower layer 2. The upper surface of the filler part 12 is shaped to define the desired profile of a flexible membrane that will form a middle skin of the rooflight, as described below.

In use, the longitudinal direction of the rooflight will be aligned with the pitch of the roof. The filler parts 12 are preferably placed at longitudinal positions to match the positions of the purlins of the roof (if known at the time of manufacture), typically at intervals of 1 to 2 metres. Alignment of the opaque fillers with the opaque purlins allows the maximum transmission of light through the rooflight and the fillers provide support between the layers of the rooflight at the points where it is fixed to the purlins. A further function of the fillers is to restrict circulation of air along the rooflight, thereby inhibiting heat transfer.

In the step shown in Figure 3, lines of hot melt adhesive 14 are deposited on top of the ribs 6 and leg 10 of the lower layer 2. Optionally, lines of silicone may also be deposited: in the illustrated embodiment a line of silicone 16 is deposited only on the leg 10. The hot melt adhesive 14 gives a sufficient bond to hold the rooflight together during manufacture and installation. The silicone 16 takes longer to cure but provides a better, more long-lasting seal.

In the step shown in Figure 4, a thin, flexible membrane 18 is laid across the lower layer 2, resting on the rib 6 and leg 10 of the lower layer 2. The membrane 18 must be transparent and stretchable. A preferred material for the membrane is a polyester film in a thickness of 20 u. m, such as Melinexo supplied by DuPont, which has good compatibility with the GRP material of the rooflight. Another suitable material for the membrane 18 might be nylon. The membrane 18 must be resistant to damage from prolonged exposure to ultraviolet light. It may be given optical properties distinct from those of the upper and lower layers but desirable for the rooflight as a whole, such as a tint or so-called solar control.

Wheels may be run along the membrane 18 on top of the rib 6 and leg 10 to press the membrane against the hot melt adhesive 14.

Figure 5 shows the next step in manufacturing the rooflight, in which upper parts 20 of the fillers are positioned above the corresponding lower parts 12. The upper parts 20 of the fillers are made of the same material and have the same width as the lower parts 12. The lower surface of the upper part 20 of the filler is shaped to conform to the upper surface of the lower part 12 of the filler. The upper surface of the upper part 20 of the filler is shaped to conform to the profile of the upper layer of the rooflight (described below).

The membrane 18 is stretched downwards by the upper parts 20 of the fillers when they are inserted. At the longitudinal positions of the fillers, the membrane 18'is then clamped between the upper and lower parts 12, 20 of the split fillers and conforms to the profile defined by the split fillers. Between those longitudinal positions, the membrane 18 remains taut between the rib 6 and leg 10 of the lower layer 2, as shown in Figure 5.

Before or after the fixing of the upper parts 20 of the split fillers, parts of the membrane 18 that extend beyond the small rib 6 of the lower layer may be trimmed away.

Prior to the next step, shown in Figure 6, the partially assembled rooflight is inverted so that the same apparatus can be used for depositing adhesive 14 on the upper layer 22 as was used on the lower layer 2.

Figure 6 shows an upper layer 22 of the rooflight, which appears at the bottom of the drawing because of the inverted configuration of the rooflight during the final manufacturing steps. The upper layer 22 is translucent and substantially rigid. In this embodiment of the invention, the lower layer is manufactured from thermoformed GRP. It has a ribbed profile, including a small rib 24 that projects upwards (when the rooflight is not inverted) near one longitudinal edge 26 of the upper layer 22, at the left side as viewed in the drawing. The other longitudinal edge 28 of the upper layer

22, at the right side as viewed in the drawing, is on a leg 30 that projects downwards (when the rooflight is not inverted).

Lines of hot melt adhesive 14 and silicone 16 are deposited along the rib 24 and leg 30 of the upper layer, as previously described with respect to the lower layer.

Next, the part-assembly including the lower layer 2 is brought into engagement with the upper layer 22 to form a complete rooflight, as shown (still inverted) in Figure 7.

The leg 10 of the lower layer 2 engages with the rib 24 of the upper layer 22 to seal the rooflight along the respective longitudinal edges 8,26. The rib 6 of the lower layer 2 engages with the leg 30 of the upper layer 22 to seal the rooflight along the respective longitudinal edges 4,28. Away from the longitudinal edges, the rigid upper and lower layers 2, 22 are spaced from one another to form a void.

At the positions of the fillers, the fillers 12,20 fill the void between the upper and lower layers 2,22 and (as previously explained) at those positions the membrane 18' conforms to the profile defined by the upper and lower parts 12,20 of the split fillers.

Between the longitudinal positions of the fillers, when the upper and lower layers 2,22 are brought together, the membrane 18 becomes clamped between the leg 10 of the lower layer and the rib 24 of the upper layer 22. However, between that point where it is clamped and the point where the membrane 18 is adhered to the rib 6 of the lower layer 2, the membrane 18 remains free and it stretches diagonally across the void as shown in Figure 7 to form a middle skin of the rooflight, separate from the upper and lower layers 2,22.

It can be seen in Figure 7 how the profile of the assembled rooflight adjacent to its longitudinal edges is such that neighbouring rooflights can be made to overlap neatly.

The reader should understand that the profiles shown are only illustrative and that a wide variety of profiles of both the upper and lower layers 2,22 are possible, generally matching the profiles of the inner lining and outer sheeting of the roof in which the rooflight is to be fitted.

In the described embodiment of the invention, the membrane 18 is trimmed along rib 6 of the lower layer 2 prior to assembly with the upper layer 22. This allows the upper and lower layers 2,22 to be in direct contact with one another adjacent to their longitudinal edges 4,28, which may help with adhesion between the layers. Adjacent to the other longitudinal edges 8,26, the membrane 18 is sandwiched between the upper and lower layers 2,22, which, depending on the material of the membrane 18 and the choice of adhesive 14, may interfere with adhesion between the upper and lower layers 2,22. To avoid sandwiching the membrane 18 in this manner, it may be possible to design a profile of the lower layer that allows the membrane 18 to be readily trimmed along both edges. Alternatively, an edge of the membrane 18 may be positioned so that it does not overlap the leg 10 of the lower layer but butts against it.

That solution requires more careful positioning of the membrane 18, which will add to --Iuires more ca-ri---- ! the manufacturing cost. It also requires a suitable surface adjacent to the leg 10 on which to adhere the edge of the membrane 18. One candidate for that surface is the small shoulder 32, which is provided to accommodate an overlapping neighbouring rooflight, but could be heightened (as shown in Figure 8) to provide a small horizontal surface above the level of the fillers. Alternatively, a strip of the same material that forms the fillers could be inserted longitudinally, resting on the shoulder 32, to provide the required horizontal surface for adhesion of the membrane 18.

It is envisaged that the rooflight previously described can readily be adapted to accommodate more than one membrane 18 and have further improved insulative properties. The most convenient method would be to split each filler into n+l parts so as to define n profiles between the parts, each profile being occupied by a different membrane 18. Another method would be to manufacture a rooflight just as previously described but with a pair of membranes occupying the place of the single membrane 18 in the illustrated embodiment. A bubble of air could then be trapped between the pair of membranes to hold them apart from one another and form separate skins.

A pair of flexible membranes 18a and 18b are shown in Figure 9. The first membrane 18a is fixed between the rib 6 of the lower layer 2 and a foam strip 34 which is

inserted longitudinally. A second membrane 18b provides additional insulation and is adhered to a pair of foam strips 36 and 38 that are mounted on the rib 6 and foam strip 34 respectively.

In Figure 10 the lower layer 2 does not have a rib 6 and the flexible membrane 18 is fixed between two foam strips 40 and 42. Before the membrane 18 is adhered to the foam strips 40,42 the lower layer can be bent slightly as shown. This causes the membrane 18 to be properly tensioned when the lower layer is released and returns to its original straight configuration.

In Figures 9 and 10, the function of any of the foam strips 34 to 42 may be performed by any elongate strip of suitable shape, for example an extrusion of polycarbonate or another plastic material.

Figure 11 shows how the flexible membrane 18 can be adhered to the inside surface of the leg 10 of the lower layer. It will be appreciated that both ends of the membrane 18 can be fixed in this way.

Claims

CLAIMS 1. A rooflight comprising: a substantially rigid upper layer and a substantially rigid lower layer, each of the upper and lower layers having opposing longitudinal edges, the upper and lower layers being attached to each other along the longitudinal edges and spaced from each other between the longitudinal edges to form a void; and a flexible membrane stretched across the void between the upper and lower layers.
2. A rooflight according to claim 1, wherein the membrane is clamped between

the upper and lower layers along at least one of the longitudinal edges. p
3. A rooflight according to claim 1, wherein the membrane is adhered to the upper or lower layer adjacent to at least one of the longitudinal edges.
4. A rooflight according to claim 2 or claim 3, wherein the upper and lower layers are generally planar; the attachment between the upper and lower layers at one of the longitudinal edges is generally in the plane of the upper layer; and the attachment between the upper and lower layers at the other of the longitudinal edges is generally in the plane of the lower layer ; whereby the membrane is stretched diagonally across the void.
5. A rooflight according to claim 3, wherein the upper layer or the lower layer includes a shoulder adjacent to one of the longitudinal edges, to which the membrane is adhered.
6. A rooflight according to claim 3, wherein a longitudinal strip of material is provided adjacent to one of the longitudinal edges of the upper or the lower layer, the longitudinal strip having a surface to which the membrane is adhered.

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7. A rooflight according to any preceding claim, further comprising narrow fillers that extend transversely across the void, the fillers being spaced at intervals in the longitudinal direction; wherein each filler comprises an upper part and a lower part, with the membrane being clamped between the upper part and the lower part.
8. A rooflight according to any preceding claim, comprising a plurality of the flexible membranes stretched across the void between the upper and lower layers and spaced from one another.
9. A rooflight according to any preceding claim, wherein the membrane is a polyester film.
10. A rooflight according to any preceding claim, wherein the upper and lower layers are formed from glass-reinforced plastic.
11. A method of manufacturing a rooflight, comprising the steps of : (a) providing a substantially rigid lower layer having opposing longitudinal edges; (b) laying a flexible membrane across the lower layer from one longitudinal edge to the other; (c) laying a substantially rigid upper layer over the lower layer and the flexible membrane; and (d) attaching the upper layer to the lower layer along their respective longitudinal edges to form a void between the upper and lower layers, with the flexible membrane being stretched across the void.
12. A method according to claim 11, wherein step (c) involves stretching of the membrane.

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13. A method according to claim 11 or claim 12, comprising the further steps of : (al) between steps (a) and (b), positioning a plurality of lower parts of narrow fillers transversely across the lower layer at intervals in the longitudinal direction; and (bl) between steps (b) and (c), positioning a plurality of upper parts of the fillers transversely across the rooflight at positions above the corresponding lower parts, so as to clamp the membrane between the respective upper and lower parts of the fillers.
14. A method according to any of claims 11 to 13, comprising the further steps of : (a2) before step (b), depositing lines of adhesive adjacent to the longitudinal edges of the lower layer; and (b2) before step (c), depositing lines of adhesive adjacent to the longitudinal edges of the upper layer.
15. A method according to claim 14, comprising the further step of : (b3) between step (b) and step (c), trimming away part of the membrane that extends beyond the line of adhesive along at least one of the longitudinal edges of the lower layer.
16. A rooflight substantially as described herein with reference to the drawings.
17. A method of manufacturing a rooflight, substantially as described herein with reference to the drawings.