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External Shading Devices

Exterior shading devices include awnings, louvers, shutters, rolling shutters and shades, and solar screens. Whilst not shown below, one of the most important external shading devices is the building itself. In many instances, the structure and form of the building can be designed such that it protects windows that may normally be exposed to direct summer sun. Balcony overhangs and inset windows are a perfect example.

Awnings

Awnings are effective because they completely block direct sunlight. They are usually made of fabric or metal and are attached above the window and extend down and out. A properly installed awning can reduce heat gain by up to 65% on north-facing windows and 77% on eastern windows. A light-coloured awning also reflects sunlight so can help reduce radiant temperatures immediately outside the window.

Maintaining a gap between the top of the awning and the side of the building helps vent accumulated heat from under a solid-surface awning. If in a climate with cold winters, it may be desirable to remove awnings for winter storage, or to install retractable ones to maximise winter heat gains.

The amount of drop (how far down the awning comes) depends on the orientation of the window. An east or west window needs a drop of at least 65% to 75% of the window height. A north-facing window needs only a drop of 30% to 50% for the same amount of shade. A pleasing angle to the eye for mounting an awning is around 45 degrees. It is also important to make sure the awning does not project into the path of foot traffic by keeping the height of its lowest point at least 2 meters above the ground.

One disadvantage of awnings is that they can block the view from inside, particularly on the east and west sides. However, slatted awnings do allow limited viewing through the upper parts of windows.

Louvres

Louvres are attractive because their adjustable slats control the level of sunlight entering the building and, depending on the design, can be manually adjusted from inside or outside. The slats can be vertical or horizontal. Louvers remain fixed and are attached to the exteriors of window frames. Careful attention to the louvre angle can allow significant winter sun penetration whilst still excluding all sun in summer.

Shutters

Shutters are movable wooden or metal coverings that, when closed, keep sunlight out. Shutters are either solid or slatted with fixed or adjustable slats. Besides reducing heat gain, they can also provide privacy and security. Some shutters help insulate windows when it is cold outside.

Roller Shutters

Roller shutters have a series of horizontal slats that run down along a track. These are the most expensive shading options, but they work very well and provide excellent security. Many exterior rolling shutters or shades can be conveniently controlled from the inside. The disadvantage, however, is that they block all light and view when fully extended.

Solar Screens

Solar screens are an external fitting to the outside of the frame that are partially transparent. They act to reduce the amount of direct sunlight entering the window and cut down overall glare without fully blocking the view or eliminating air flow. They also provide privacy by restricting the view of the interior from outside the building. Solar screens come in a variety of colours and different materials with weaves that offer varying degrees of sun control. Some screens are also partially reflective, further reducing sun penetration.

Interior Shades

Although interior shading is not as effective as exterior shading, it is worthwhile if no external technique is possible. There are a number of different types.

Curtains and Drapes

Draperies and curtains made of tightly woven, light-coloured, opaque fabrics reflect more of short-wave solar radiation back out the window than they let through. The tighter the curtain is against the wall around the window, the better it will prevent heat gain. Two distinct layers improve the effectiveness of the draperies insulation when it is either hot or cold outside.

Venetian Blinds

Blinds, although not as effective as drapes, can be adjusted to let in some light and air while reflecting some of the heat. Some newer blinds are coated with reflective finishes for increase their effectiveness. To be effective, the reflective surfaces must face the outdoor side.

Cellular Shades

Cellular or honeycomb shades are similar to window shades, but are constructed from two layers of material with an air-gap between. This allows them to be raised and lowered easily, and also increases the thermal resistance of the overall window slightly. Some interior cellular shades also come with a reflective mylar coating. When down, these shades block the majority of natural light and restrict air flow.

Roller Blinds

Opaque roller shades are simply a thin sheet of material that unrolls down behind the window to reduce direct sun penetration. They are reasonably effective when fully drawn but also block light and restrict air flow.