GB2284835A - Rainscreen cassette - Google Patents

Abstract

A rainscreen cassette overcladding system for a building, the system comprising a number of cladding panels (11, 11') and a support structure made up of a number of brackets (8) secured to the wall of the building and a number of vertical support mullions (1, 1') mounted in the brackets (8). The support mullions (1, 1') are each provided on opposing sides with longitudinally extending flanges (2) to which the cladding panels (11, 11') may be secured, e.g. by self-tapping screws, and by hooks (13) which co-operate with rods (4) on mullions (1). <IMAGE>

Description

IMPROVED RAINSCREEN CASSETTE This invention relates to improvements in building overcladding systems, and in particular, but not exclusively, to aluminium rainscreen cassette systems.

Since the mid-1970s, it has been known to provide buildings, particularly high- or low-rise tower blocks, with an overcladding of one form or another. The purpose of the overcladding is mainly to protect the fabric of a building from damage and erosion caused by wind, rain and solar radiation, but the overcladding may also serve to provide insulation and to improve the aesthetic appearance of the building.

One method of overcladding is the render system, which is mainly applied in low-rise refurbishments. In the render system, mineral or polystyrene insulation is externally secured to the existing building structure either by way of 'through face' fixings, or by way of a railing system. A render, which will generally be polymer-modified, is then trowelled onto the external face of the insulation in one or more coats in order to achieve a specified thickness. Reinforcing mesh may be incorporated for extra strength, particularly around openings such as window reveals and soffits. With the render system, it is very important to ensure weather proofing around openings including aluminium or uPVC cill sections. If water breaches the render, the effectiveness of the insulation is impaired and damage to the building may result.

A more recent alternative to the render system is the board system. The support structure in the board system comprises aluminium brackets anchored back to the existing structure. These brackets support vertical spanning aluminium 'T'-section rails.

Insulation is fixed to the external elevations of the existing structure and the specified fire stopping detail is constructed. Flat boards, generally comprising laminated or glass reinforced plastic panels, are offered up to the T' rails and face-fixed using pop rivets. Thermal and moisture expansion and contraction are accommodated by the fixings. Vertical joins between panels are formed via the 'T rails which create drainage channels. Horizontal joins between panels may be left open, or may be provided with an aluminium or uPVC joint with a 'chair' section. The board system also suffers the disadvantage that water penetration can impair the effectiveness of the insulation and result in damage to the building.

The most versatile and effective overcladding system is the aluminium rainscreen cassette system.

This system provides a back-ventilated and drained aluminium cladding envelope designed to achieve internal and external pressure equalisation and to protect external walls from rain wetting and solar radiation. An insulating material, such as mineral wool, is secured to the existing facade. A support structure is then fixed to the building through the insulation material. The support structure is attached by means of a number of brackets bolted onto the building at floor levels by way of steel bolts.

Vertically running support mullions are then bolted onto the brackets, and a rainscreen is then built onto the support structure by means of panels which are hooked onto the support mullions. The panels are generally made out of aluminium, and may be polyester powder coated in a variety of colours. This type of installation provides a ventilated cavity behind the rainscreen which helps to reduce condensation, assist the evaporation of ingressed moisture, and which allows the original fabric of the building to breathe. These advantages of the rainscreen cassette system arise from the fact that the panels are disposed on the vertical support mullions in such a way that rain can pass between horizontally adjacent panels, and can then run down to ground level via channels provided in the vertical support mullions. The horizontal joins between vertically adjacent panels are designed to allow rain through, but to reduce its momentum by means of deflection flanges. Consequently, any rain which penetrates the rainscreen will run down the inside of the ventilated cavity. Since the rainscreen is not an impervious curtain wall, such a breach of the rainscreen does not lead to structural failure, since the ventilation allows the ingressed moisture to evaporate. Furthermore, any condensation build-up behind the rainscreen is also allowed to evaporate.

There are a number of disadvantages associated with the known construction of rainscreen cassette systems described above. The panels are attached to the support structure by way of notches which hook over horizontal bars provided on the vertical support mullions, and also by way of an interlock arrangement between vertically adjacent panels. This method of attachment, while allowing for thermal expansion, is not secure against strong upward wind forces. It has been known, especially on housing estates where a number of rainscreen cassette-clad buildings are close together, for the panels to peel off due to the uplift generated by strong winds. Furthermore, because the brackets to which the support mullions are attached can only be secured to the existing building frame at floor levels, which are generally around 2.5m apart, the support mullions have to have a relatively large box section in order to provide the necessary rigidity for the support structure. For example, the total distance from the original building fabric to the rainscreen is generally around 170mm, with the insulation material taking up around 50mm and the depth of the vertical support mullion taking up around 120mm. This structural requirement of known rainscreen cassettes means that window recesses are correspondingly relatively deep. Apart from any aesthetic disadvantages, such deep window recesses encourage the formation of wind eddies which can provide an uplift sufficient to unhook the panels from the support structure. Yet another disadvantage associated with known support structures arises from the inflexible nature of the bolted connection between the support mullions and the brackets. In order to achieve a uniform panelling surface regardless of structural irregularities in the fabric of the building itself, it is necessary to install the brackets to an extremely high tolerance prior to fitting the support mullions, i.e. the brackets on each face of the building have to be installed so that their points of attachment to the support mullions all fall within a predetermined, generally vertical plane, regardless of any anomalies in the building fabric. It is generally very difficult to adjust the projection of a bracket from the face of the building after it has been fitted, since the structural integrity of its connection to the building may be compromised.

The vertical support mullions do not generally extend the height of the building being clad, but are installed in shorter lengths. Since support brackets may only be installed at floor levels, it is not generally possible to provide support at both ends of any particular mullion. Furthermore, the gaps between vertically adjacent support mullions allow water to penetrate the rainscreen.

It is an object of the present invention to provide a rainscreen cladding system which alleviates these disadvantages.

According to a first aspect of the present invention, there is provided a support mullion for use in a rainscreen cladding system, which support mullion is provided on two opposing sides with a longitudinally extending flange to which rainscreen panels may be bolted when said support mullion is installed as part of a rainscreen cladding system.

The flanges are preferably arranged in such a way that a horizontal section through a support mullion is of a 'top hat' configuration. Upon installation, the rainscreen panels are secured to the flanges, preferably by means of self-tapping screws which pass through holes in the panels. Alternatively, the panels may be secured to the flanges by means of bolts which pass through the holes in the panels and holes provided at appropriate locations in the flanges. In order to allow for thermal expansion and contraction, it is advantageous for the holes in the rainscreen panels to be slot-shaped. This fixing arrangement is provided primarily in order to prevent the rainscreen panels from being lifted off the support structure, the greater proportion of the weight of the panels being supported by the previously described notch and bar arrangement. However, the present invention also provides an improvement over the known notch and bar arrangement through the provision of a U-shaped rubber clip, which is advantageously made out of ethyl propylene diene monomer (EPDM) or a similar suitable material. The clip is adapted to line the notches in the rainscreen panels, and is arranged so that its mouth is narrower than its internal width. This allows the rainscreen panels to be clipped onto the bar rather than merely being suspended.

In addition to providing a surface to which the rainscreen panels may be securely attached, the flanges give the support mullion of the present invention greater structural rigidity than the known type of mullion described above. This means that the box section of the mullion of the present invention may be smaller than that of a conventional mullion, enabling the rainscreen panels to be installed closer to the original fabric of a building. In certain embodiments of the present invention, the box section of the support mullion is such that, when a rainscreen is installed, the total distance from the original building fabric to the rainscreen panels is from 100mm to 150mm, preferably from 120mm to 130mm, as compared to known rainscreen cassette installations where the building to panel distance is generally around 170mm. The reduction in the building to panel distance, which is achieved through the relatively greater structural rigidity provided by the flanges of the mullions of the present invention, gives rise to the advantageous effect that the window recesses (which are the insets from the rainscreen layer to the windows of the clad building) are shallower than in conventionally clad buildings, and the uplifts caused by wind eddies are accordingly reduced.

According to a second aspect of the present invention, there is provided a support mullion for use in a rainscreen cladding system, which support mullion is provided on two opposing sides with longitudinally extending teeth, which teeth, when the support mullion is installed by means of brackets secured to the face of a building, mesh with corresponding teeth provided on the inner surfaces of the arms of the brackets.

This second aspect of the present invention enables the support mullions to be accurately installed so as to define a uniform plane without the need to ensure that all the brackets are installed so as to define a correspondingly uniform plane. This is achieved by way of the adjustable 'snap' fit afforded by the meshing of the teeth of the mullion and the teeth of the bracket. To install a support mullion of this aspect of the invention, the mullion is brought up to the appropriate bracket or brackets and is gently tapped in. Each tap moves the mullion further between the arms of the bracket by a predetermined number of tooth steps, advantageously one tooth step per tap. In preferred embodiments, this tapping process may be controlled by laser beam measuring equipment, which allows the position and orientation of the support mullion to be determined highly accurately relative to a predetermined reference point.

The spatial period of the teeth on both the mullion and the bracket is advantageously from O.lmm to lOmm, preferably from 0.5mm to 2mm. In a currently preferred embodiment, a spatial period of lmm is specified.

The brackets themselves are secured to the building by means of anchors which are sunk into the building at floor levels. Each anchor is adapted to receive a screw which passes through the rear face of the bracket. The screw may be grouted into place, or alternatively, the anchor may be provided with a capsule containing a chemical grout or other suitable adhesive such as Loctite (TM). As the screw is being fitted into the anchor, the capsule breaks, and the adhesive is released, thereby securing the screw firmly in the anchor.

According to a third aspect of the present invention, there is provided a support mullion for use in a rainscreen cladding system, which support mullion is adapted to receive an internal sleeve, which sleeve, when said rainscreen cladding system is installed, bridges the gap between vertically adjacent support mullions.

The internal sleeve is advantageously secured in such a way as to allow thermal expansion, preferably through being bolted, welded or secured by self-tapping screws to only one of the support mullions.

Alternatively or in addition, slot-shaped holes may be provided in any one or more of the sleeve, the upper mullion and the lower mullion. The internal sleeve, as well as providing increased rigidity, also helps to prevent the leakage of draining water from between adjacent support mullions.

According to a fourth aspect of the present invention, there is provided a window panel for use with the support mullion hereinbefore described, which window panel comprises a rainscreen panel incorporating a window, wherein the window, upon installation as part of a rainscreen cassette, is adapted to be located in the same plane as the wall of the structure on which it is installed.

Preferably, the window is sealed to the cill of the window panel by means of a gasket, which may be made out of EPDM. The head of the window, however, is preferably not sealed to the panel; this allows drainage of ingressed water and increases air circulation. A secondary cill tray is advantageously provided beneath the gasket between the window and the panel at the cill of the window. This secondary cill tray collects ingressed water and condensation, and discharges this to the channels provided in the support mullions.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: FIGURE 1 shows two adjoining flanged support mullions and an associated support bracket; FIGURE 2 shows the support bracket of Figure 1; FIGURE 3 shows a support mullion and a rainscreen panel; FIGURE 4 shows an exploded view of a rainscreen cassette system installed on a building; FIGURE 5 shows an EPDM clip; FIGURE 6 shows an exploded view of the attachment between a support bracket and the wall of a building; FIGURE 7 shows a window section rainscreen panel; FIGURE 8 shows in cross-section the head of the window panel of Figure 7; and FIGURE 9 shows in cross-section the cill of the window panel of Figure 7.

Each support mullion 1, 1' of Figure 1 is provided with a pair of flanges 2. The support mullions are also provided, at predetermined locations, with internal cross-bars 4 (see Figure 3). Adjacent support mullions 1, 1' are connected by an internal sleeve 5, which is fixed to the upper support mullion 1 by means of self-tapping screws 6. On each side of the support mullions 1, 1' there are provided sets of longitudinally extending teeth 7. The support bracket 8 is provided with a corresponding set of teeth 9, which mesh with the teeth 7 and enable the support mullion to be accurately positioned before being secured to the support bracket 8 by means of bolt 20.

The support bracket 8 is embedded in the structure of the building (see Figure 4) by anchoring means 10. The support bracket 8 is shown in more detail in Figure 2, which shows the bolt 20 passing through slot-shaped holes 22, which allow for thermal expansion and contraction.

Rainscreen panels 11 are installed on the support mullions 1 by way of notches 13 which fit over crossbars 4, as shown in Figure 3. The panels are fixedly secured to the flanges 2 of the support mullions 1 by self-tapping screws 12. The depth d of the box section 21 of the support mullion is typically 50mm less than in support mullions of the known type. This is possible because the flanges 2 give additional rigidity to the support mullion. This reduction in box section allows the rainscreen panels to be positioned closer to the wall of the building, thereby reducing the effects of wind eddies which may form at window recesses.

A rainscreen cassette installation is shown in exploded form in Figure 4. Adjacent rainscreen panels 11, 11' are adapted so as to be individually removable from the support structure. This is achieved by removing the self-tapping screws 12 as appropriate and lifting out the required panel. This enables relatively trouble-free maintenance and checking to be carried out after installation. Insulating material 23 is provided at the surface of the building on which the rainscreen is being installed.

The rainscreen panel 11' of Figure 4 is provided with a notch 13 which fits over the cross-bar 4 of the support mullion 1. The notch 13 is provided with an EPDM rubber clip 14 which helps to hold the rainscreen panel 11 in place. The mouth 15 of the rubber clip 14 is narrowed, as shown in Figure 5.

The anchoring means 10 is shown in exploded detail in Figure 6. The anchor 10 is embedded in the wall of a building (see Figure 4) at a predetermined location.

The anchor 10 includes a hole 16 adapted to receive a screw 17, which attaches the support bracket 8 securely to the building via washers 18. The end of the hole 16 is provided with a capsule 19 which contains a suitable adhesive. As the screw 17 is fitted into the hole 16, the capsule 19 is broken and thereby releases the adhesive which ensures a secure fit.

Figure 7 shows a rainscreen panel 24 adapted for use at windows. This panel is generally identical to the plain panels 11 at its extremities, but is provided with a return portion 25 and a window pane 26, which are adapted to fit into existing window cut-outs in the building being clad.

Figure 8 shows in cross-section the top of a window installation comprising a rainscreen panel 24 with a return 25 and a window frame 27. There is no gasket at the interface 28 between the return 25 and the window frame 27 at the head of the window in order to allow drainage and air circulation.

At the window cill, shown in cross-section in Figure 9, an EPDM gasket 29 is provided between the window frame 27 and the return 25. This is in order to hinder the ingress of excess water. Any water which does penetrate the gasket, or which condenses under the return 25, is collected by a secondary cill tray 30 which discharges the water to the channels provided in the support structure.

Claims (8)

CLAIMS:

1. A rainscreen cladding system for a building, the system comprising a support structure and a number of cladding panels, characterised in that the support structure includes a number of support mullions each provided on opposing sides with longitudinally extending flanges to which the cladding panels may be secured when the system is installed.

2. A system as claimed in claim 1, wherein the cladding panels are provided with notches each of which is adapted, upon installation of the cladding panels to hook onto generally horizontal bars provided on the support mullions, characterised in that the notches in the cladding panels are provided with generally Ushaped rubber clips.

3. A system as claimed in claim 1 or 2, wherein the support mullions are mounted in brackets secured to the wall of the building, characterised in that the brackets comprise two arms provided on their inner surfaces with substantially longitudinally extending teeth, and in that the support mullions are provided with complementary teeth which mesh with the teeth on the brackets when the support mullions are installed.

4. A system as claimed in claim 1, 2 or 3, characterised in that the support mullions are adapted to receive and are provided with internal sleeves, which sleeves, when the system is installed, bridge the gap between vertically adjacent support mullions.

5. A system as claimed in any preceding claim, characterised in that at least one of the cladding panels incorporates a window, which window, when the cladding panels are installed, is located substantially in the same plane as the wall of the building.

6. A system as claimed in any preceding claim, wherein a number of anchors adapted to retain the support structure are sunk into the wall of the building, characterised in that at least one of the anchors is provided with a capsule containing chemical grout or adhesive, the capsule being adapted to release its contents when the support structure is mounted in the anchors.

7. A system as claimed in any preceding claim, characterised in that the box section of the support mullions is such that the distance between the wall of the building to the inner surface of the cladding panels is from lOOmm to 150mm.

8. A rainscreen cladding system for a building, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.