Closed Cavity Façade (CCF)
Closed Cavity Façade (CCF)
State of the art façade system - best performance
The energy sustainability of a building is primarily determined by the interaction between the facade and the building’s climate control system. An intelligent facade’ – the Closed Cavity Facade – which meets all physical, energy and daylight requirements –allows sustainable and therefore future oriented planning goals to be achieved.
In its original form, the Closed Cavity Facade is a completely enclosed double-skin facade design with internal triple glazing and external single glazing. It does not allow natural window ventilation. However, a combination with natural window ventilation is possible. Truly energy-efficient solar control elements enclosed in the interstitial space of a hermetically sealed facade are completely protected from weather.
With regard to the energy efficiency of the solar control – as well as all other energy, use-related and operational issues – the Closed Cavity Facade combines the benefits of a normal rear-ventilated double-skin facade with the benefits of a single-skin facade.
Switzerland’s tallest high-rise in Basel
At 178 meters, Building 1 of the pharmaceutical company F. Hoffmann-La Roche is currently the highest building in Switzerland. Designed by the architectural firm Herzog & de Meuron, it features a Closed Cavity Facade. The building sets new standards in energy conservation and sustainability. For the first time, product-neutral planning fully exploits all energy and physical potential to achieve economy and acceptable levels of expenditure.
Glass selection only offers limited potential
The materials used for facades – and their thermal insulation values – only offer minor potential for improvement. No great advances are expected here in the short and medium term, as affordable sensational new energy-saving’ materials are not on the horizon. This applies particularly to glass which, for esthetic and architectural reasons, is the material of choice for most office and commercial buildings. At the same time, thermal insulation requirements have become more stringent. This has resulted in huge advances in insulating glass in recent years. Triple glazing with Ug values of 0.6 to 0.7 W/m2K has become the affordable standard. Vacuum glazing achieving Ug values of 0.4 to 0.5 W/m2K is not currently manufactured in large series. The improvement in U value over triple glazing is comparatively small, and product and liability risks have not been resolved – there are still problems with pane spacers and the edge seal. If the seal is even slightly compromised, the element is practically worthless. As a result, the choice for the internal glazing of the Closed Cavity Facade was almost logical: Triple glazing with a light solar control coating was selected that ensures a Ug value of 0.6 W/m2K.
Significantly slimmer facade profiles
The absence of casement windows – and their double frames – means that the facade profiles, which only have to hold fixed glazing on both sides, are significantly slimmer and almost flush with the glass, resulting in a more attractive appearance. This approach also allows the use of substantially larger glass formats compared to a normal double-skin facade. To the delight of the architects, this means that glazing across two office grid sections is no problem technically.
Significantly lower cleaning costs
A significant disadvantage of a normal double-skin facade compared to a singleskin facade is the fact that the normal double-skin facade has twice as much glass surface that has to be cleaned. Depending on the location, such cleaning may be required two or three times a year. This is not the case for the Closed Cavity Facade. The fact that the facade cavity cannot be opened means that only the internal and external glass surfaces of the facade unit have to be cleaned – and not the surfaces facing into the cavity. So the same amount of window cleaning as for a single-skin facade. And better still, the solar control elements – such as venetian blinds with their many light-colored narrow aluminum slats – are sealed in the cavity and never have to be cleaned again.
Depending on the size of the building, the cost savings over the 25-year life of a building are substantial and may exceed one million. As a result, the Closed Cavity Facade is the preferred option for countries or cities in which cleaning two or three times a year is not sufficient because of high levels of air pollution
Another goal of the technical mockup test series was to ensure that both the cavity and elements installed in the cavity are maintenance-free. This was required because the cavity seal can result in peak temperatures of up to 85 °C in extreme cases. The solar control elements must perform flawlessly even under these conditions. Also, there must be no material abrasion resulting from 20,000 cycles of opening and closing the solar control and light deflection system. All long-term tests have been completed successfully to date. The only part requiring maintenance – the solar control system motor – has been relocated from the cavity to the adjacent suspended ceiling, allowing access for maintenance.