Architecture Notes

Why create a double skin facade?  The idea typically comes up when discussing a tall building.  Tall buildings lead to the desire to have expansive views and a great deal of glass.  If you create an all glass building, It takes a great deal of mechanical ventilation, and thus energy, to keep it cool in the summer and warm in the winter.  To mitigate this setback, the concept of the double skin facade can improve the thermal comfort, acoustic isolation from the exterior and potentially the energy efficiency of the building.  In a nutshell, we’re talking about 2 layers of glass and and intermediate space or cavity.  The cavity is a space of mediation between the interior and exterior enviroment.  Here is an excellent break down from this report available online:

This concept is manifested with a single exterior layer of heat-strengthened

safety glass or laminated safety glass, with exterior air inlet and outlet

openings controlled with manual or automatic throttling flaps. The second

interior façade layer consists of fixed or operable, double or single-pane, casement

or hopper windows. Within the intermediate space are retractable or

fixed Venetian blinds or roller shades, whose operation can be manual or

automated. During cooling conditions, the Venetian blinds (or roller shades)

cover the full height of the façade and are tilted to block direct sun. Absorbed

solar radiation is either convected within the intermediate space or re-radiIntroduction

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ated to the interior and exterior. Low-emittance coatings on the interior glass

façade reduce radiative heat gains to the interior. If operable, the interior

windows are closed. Convection within the intermediate cavity occurs either

through thermal buoyancy or is wind driven. In some cases, mechanical ventilation

is used to extract heat”.

This concept is manifested with a single exterior layer of heat-strengthened safety glass or laminated safety glass, with exterior air inlet and outlet openings controlled with manual or automatic throttling flaps. The second interior façade layer consists of fixed or operable, double or single-pane, casement or hopper windows. Within the intermediate space are retractable or fixed Venetian blinds or roller shades, whose operation can be manual or automated. During cooling conditions, the Venetian blinds (or roller shades) cover the full height of the façade and are tilted to block direct sun. Absorbed solar radiation is either convected within the intermediate space or re-radiated to the interior and exterior. Low-emittance coatings on the interior glass façade reduce radiative heat gains to the interior. If operable, the interior windows are closed. Convection within the intermediate cavity occurs either through thermal buoyancy or is wind driven. In some cases, mechanical ventilation is used to extract heat.

Warm or Cool Climates

In a cool climate, the solar gain in the cavity can be circulated into the occupied space to offset mechanical ventilation requirements.  In a warm climate, the cavity is vented; the hot air rises, vents out and pulls in cooler air behind it.  This cooler cavity space reduces cooling requirements within the occupied space.

Types

Box Windows:  Consists of framed inward swinging window.  The cavity  is divided horizontally.  Vertical divisions of the cavity at every bay prevent the spread of sounds and smells from room to room.  Suited for solid facades with punched openings.

Shaft Box:  Special form of box windowed facade. Facade alternates between box windows and vertical shafts.  Shaft-box facades require fewer openings on the outside layer.  This system is best suited for lower rise construction.

Corridor Facade:  Intermediate space is closed at each floor.  Special care should be taken to prevent sound transmission from room to room via the corridor.  Best where high levels of sound insulation is required between rooms.

Multistory Facade:  Intermediate space is open with horizontal division.  In winter, the facade can be closed at top and bottom to exploit the conservatory effect and optimize solar energy gains.  Like corridor facades, special care should be taken acoustically.

Criticisms

From Wikipedia

The advantages of double skin facades over conventional single skin facades is not clear-cut; similar insulative values may be obtained using conventional high performance, low-e windows. The cavity results in a decrease in usable floor space, and depending on the strategy for ventilating the cavity it may have problems with condensation, becoming soiled or introducing outside noise. The construction of a second skin may also present a significant increase in materials and design costs.

Building energy modeling of double skin facades is inherently more difficult because of varying heat transfer properties within the cavity, making the modeling of energy performance and the prediction of savings debatable.