Cud

6.26 Dimensions of panels used at Bronx Centre, New York (architect: Richard Meier).

made near-maximum use of available rolled sheet sizes. Some curved panels were also used on the projecting staircase enclosures, 3.6 m high x 0.862 m wide (Fig. 6.26). Because of cost, plasterboard linings were selected for this project, and it is interesting to note that the curved corners to the windows had to be made good in plaster on the inside face. Figure 6.27 shows detail from the Johnson & Johnson building, which incorporates a gutter system at the base of the panels to collect any water that may penetrate the sealant (usually silicone) joint system. Weepholes are also provided to discharge the water to the outside face. Also note the method of'floating'the aluminium sheet

Stud weld and slotted hole to allow movement

Silicone mastic seal

4 mm rolled aluminium sheet

Stud weld and slotted hole to allow movement

Silicone mastic seal

4 mm rolled aluminium sheet

Weephole to gutter section

Site-applied sealant from front face

Site-applied sealant from front face

Gutter section

Weep tube

6.27 Horizontal joint detail from Johnson & Johnson building, New Brunswick, USA (architect: I.M. Pei).

Gutter section

Weep tube

6.27 Horizontal joint detail from Johnson & Johnson building, New Brunswick, USA (architect: I.M. Pei).

onto the panel framework, using studs welded onto the sheet with slotted holes to permit thermal movement.

European examples of rolled sheet panel construction would include the Hochhaus Dresdner Bank in Frankfurt (panels by Josef Gartner; architects: Becker; Becker and Partners). Here the panels consist of 2.5 mm aluminium rolled sheet outer skin, which is deep drawn into a tray and screwed to an aluminium carrier system. Figure 6.28 shows the junction between two panels where the carrier is in four sections forming the outer and inner parts of the assembly. The aluminium skin is fixed to the outer section of the carrier; which is screwed from the inner section by a thermal

Inner section fixed back to structure

Inner lining

Insulated / inner panel

Inner lining

Inner section fixed back to structure

Insulated / inner panel

Insulated inner panel

Outside

2.5 mm aluminium panels screwed to framing

Insulated inner panel

Outside

2.5 mm aluminium panels screwed to framing

6.28 Plan of joint between panels at Hochhaus Dresdner Bank, Frankfurt (architects: Becker; Becker and Partners).

break. The inner lining is bolted back to the main structural framing.

Rain screen panels

This last type of panel is in effect a combination of rolled sheet and laminated panel in which a flat aluminium sheet 4-6 mm thick is mounted in front of a laminated panel, itself designed for weather resistance with a ventilated cavity between the two parts of the construction. As the name 'screen' suggests, these

Profiled rain screen panels hooked on to pins to aluminium carrier system

Profiled rain screen panels hooked on to pins to aluminium carrier system

Floor slab

Rain screen panel

Double glazed unit

6.29 Section of panels used at Umschlags AG office building, Basel (architects: Wetterwald and Wenger).

Floor slab

Rain screen panel

Double glazed unit

6.29 Section of panels used at Umschlags AG office building, Basel (architects: Wetterwald and Wenger).

panels are only a first-stage barrier The panels behind provide the thermal and acoustic performance, and can be mounted Into a carrier system or fixed to secondary framing in the same way as previously described.The joints between the rain screen panels should be 10 mm or more to allow for any thermal movement, and it is also advised that the fixing of the outer sheets to the carrier system should allow for movement.The gauge of the plate panel must also be such as to avoid rippling and distortion of the sheet (in aluminium, 4-6 mm). For a further discussion of rain screen and pressure-equalized wall design, see the AAMA (I 971), and Chapter 7 on curtain walling. This system of construction was used at the Umschlags

AG office building in Basel (Fig. 6.29) (architects: Wetterwald and Wenger), where 165 I mm wide x 2060 mm high decorative aluminium panels were deep drawn by Schmidlin and in effect 'hooked' onto the building, with an air gap of 20-30 mm provided between the outer panel and the insulation to ensure ventilation of the rain screen principle. Figure 6.30 shows a UK example of a rain screen, showing the air gap, the method of clipping the rain screen to the carrier; and the thermal break.

The size of the panel is limited only by the maximum size of the sheet metal panel and its ability to span between supports. However; the outside face of the inner laminated panel must also be waterproof, and this may limit the size of the overall assembly if joints in this panel are to be avoided. Rain screen panel principles have also been developed for over-cladding using metal panels mounted onto concrete block back-up walls.

These metal panels (usually powder-coated aluminium) are fixed to supporting mullions fixed in

Insulated cladding panel

Rain screen panel —

Patent interlocking thermal break

Insulated cladding panel

Rain screen panel —

Patent interlocking thermal break

Neoprene seals — Double glazing

Inner insulated panel

For louvre drape

Inner insulated panel

Neoprene seals — Double glazing

6.30 Typical rain screen detail (section).

turn back to the external building fabric. A cavity is usually formed between the original and the new fabric, which is insulated, normally with mineral fibre insulation. Panels are normally locked to the supporting mullions by stainless steel pins, either exposed or secret fixed, with the joint forming a rain screen mounted on brackets fixed to the blockwork or brickwork wall behind (Fig. 6.3 I).

The Knowsley fire in Liverpool (Bolland, 1991) raised questions on fire spreading through cavities within this type of assembly, and the need for fire stops at floor levels and around window openings. There is an essential conflict between the need for horizontal fire stops and the provision of ventilated cavities.

Fire tests on board products undertaken at Cardington (BRE, 1989) indicated that some benefits of fire spread may result from reducing the width of the cavity, but clearly the amount of air movement to ensure proper ventilation of the system to avoid condensation will need to be checked.

6.31 Typical secret fixing using metal pins for rain screen cladding.

The situation of wind loading on the inner face of the cavity is also not clear Work by N. J. Cook (Building Research Establishment) on dynamic wind effects on board products with open joints has shown that fluctuations in wind pressure are transmitted through open joints to act directly on the original wall. Manufacturers should be asked to confirm their assumptions on wind loading when specifying the fixings and type of back-up wall.

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