This project demonstrates an innovative use of architectural façade glazing to an entire retail and office park. We as Specialist Façade Contractors were integral to its development. Our Early engagements at design stage allowed us to architecturally façade engineer this frameless fenestration. Value engineering and risk management been critical features of our in-house approach.
The Specialist Façade Contracting workpackage included:
- Frameless architecturally glazing to showroom areas.
- Integrated windows into composite kingspan panels.
- Capped Curtain walling to commercial retail park.
- Architectural midspan louvers.
- Frameless revolving door.
The face glass to the showroom areas is 20.5mm toughened/laminated single glazing. Each unit is typically 3000mm high by 2000mm wide. A number of glass risks were identified:
- Roller wave distortion was a concern, discussion with the glass supplier led to an agreed manufacturing methodology so that its effect was minimised so that the external appearance was flat.
- The Toughening process introduces the risk of Nickel Sulphide inclusion (NSI). To reduce this risk, the glass is Heat Soak Tested (HST). Heat soak testing does not eliminate the risk entirely but certainly a step in the right direction.
- A laminate interlayer had to be used that did not react adversely to weathering and material use. The ionoplast interlayer was chosen for its resilient qualities.
Glass Performance requirements
Single glazing of this type has poor u-values, poor solar gain control but excellent light transmission.
Factoring this into the design, solar gain is managed by external horizontal shading. This has an independent structure, standing outside of the façade solution.
Improving the u-value would require the alteration of the glazing configuration from single to double glazing.
In practice this would require the alteration of the façade fenestration. Each intermediate single pane presently spans unsupported, captivated top and bottom. Double glazing would introduce the requirement for fritting and secondary glass fins.
These options were all considered as part of the overall project life cycle and value engineering approach.
Screens sizes were procured to suit the availability of face glass to suit standard 3000mm by 2000mm toughening sizes. Sizes determined at design stage as availability of larger sizes limited to a smaller supplier network. Using Value engineering, the sizes reflect commercial availability enabling a more completive workpackage.
Frameless Façade Construction
The show room glazing is in effect frameless. Structural openings widths vary but the heights are typically 6m.
The perimeter framework is a 60mm stick curtain wall system. Mullions run up the jambs, transoms run across the base, head and intermediate I beam.
Horizontally the transom is connected to a horizontal 1m castellated steel beam. This beam is supported by vertical columns which stand at 6m centres. All connections are visible and typically of industrial architectural glazing solutions.
The transom is positioned as necessary to allow the face glass run through. The transom is fixed at 900mm centres. A flat plate is located to the underside of the transom connects it to the predrilled steel flange. Transom lengths are typically 6m and sleeved to allow for continuous runs.
Vertically at the jambs, the mullion is full height; the castellated beam is notched to allow it run through. It also acts as a midspan support.
At the base, the cast in situ floor is rebated; set out to an agreed line, the aluminium base plate is concealed beneath the floor finish.
At the head, the horizontal transom is fixed to secondary steel I beam.
Secondary Steelwork Design
The 1m high horizontal I beam has castellated profiled openings which allow natural daylight to penetrate internally into the deep retail space. Its aesthetics was an important consideration in the external visual appearance of the façade solution.
This beam is designed to ensure that at this level, no deflections will occur under load. All the intermediate face glass is two edge supported, captivated into a 15mm glazing rebate, the glazing rebate size was an important factor in the I beams design in respect of limiting deflections under wind and dead load.
The horizontal transom profile incorporates reinforced glazing shoes to transmit the glass loads back to the castellated I beam structure.
The transom is preped along its length for drainage with suitably drainage slots and is captiated by a external pressure plate and cap.
The overhead brise soleil projects 2.5 m from the face of the building and has specifically designed to provide protection from overheating in the summer months whilst allowing satisfactory light transmission in the heating months.
The minimalist approach, The solution is articulated by 10mm silicon joints at 2m centres, a 60mm horizontal pressure plate and cap and the structure which makes a contrasting architectural statement to the internal white finish.