Solar Shading

Proper use of solar shading can save you money and prevent over heating in your home. Everyone likes a house with lots of windows to give their home abundant natural light from the sun. The downside to this is that when summer comes around, the house has a tendency to overheat, feels humid and stuffy, and you turn on the air conditioning, running up energy costs.

Solar shading is the term used by architects, engineers and building system designers referring to a range of passive techniques to deal with overheating due to sun exposure on a building’s exterior. It encompasses:

- External Shading
- Window Glazing and Films
- Internal Blinds

As an alternative to air conditioning, a well designed house incorporating solar shading can achieve equal comfort with zero energy consumption, in combination with night-time ventilation. Designers must also take into account other aspects of the house; for example, blocking too much sunlight could cause additional energy use in lighting, or in winter, additional heating.

Other factors which affect overall residential overheating include heat from appliances, hot water showers, and cooking, number of occupants, hot water storage, average daytime temperature, the home’s insulation and it’s ventilation properties.

Of course, in more temperate areas, high humidity may necessitate the use of air conditioning, but in such a case, solar shading can still be used to cut down energy costs.

External Window Shading

The goal of external shading is to prevent sunlight from reaching a window. It is the single most effective method to reduce overheating. A few types of external shading are:

- Overhang: a horizontally projecting structure installed above the window. They protect well against high angle summer sun, especially on windows facing south. They allow the windows to be open and do not hinder the view.

- Light Shelf: a type of overhang installed half-way up a window, usually just above an average sized occupant’s head height.

- Awnings: Usually reserved for larger sized windows, awnings can work well on smaller windows as well, depending on the house. Retractable awnings are available and allow for use only when needed.

- External Blinds: many types are available, from roller type to vertical or horizontal slat type. Blinds cover the exterior of a window and provide good flexibility of use. Avoid horizontal louvred or slatted blinds, as they have the lowest shading factor of any external shading system.

Window Glazing and Films

Depending on the type of glass used in a window, sunlight can the resulting heat can be either reflected, transmitted or absorbed. Commercial construction has adopted the use of solar control glass, and residential use is becoming more widespread. Solar control glass can be either absorbent or reflective, with reflective being the more efficient type.

Specialized glazing has been introduced recently which reduces heat transmission while at the same time transmitting acceptable levels of light. This type of glass includes a coating which only reflects light in the infrared portion of the spectrum. The coating also reduces heat loss in winter, similar to the way low-e glass does.

Solar control films are also available, these can be retrofitted to existing flat pane glazing windows. Film tends to be less durable than specially designed glazing, but it can still be more cost effective than standard glazing windows.

Interior Window Blinds

Blinds on the inside of a window can help reduce overheating, but are not as effective as external forms of solar shading. This is due to the fact that the blind’s material tends to absorb solar heat and convect it out into the home’s interior. Solar reflective coating on fabrics can alleviate some of this absorption and will transmit less heat than conventional fabric blinds.

Roller blinds made of reflective opaque film instead of fabric are a good alternative to control solar heating. They offer solar shading characteristics similar to external window films, but give you the option to revert back to no shading on days when more lighting and solar heat is needed.

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