Lesson 8 – Sun-shading in Natural Building

What is sun-shading?

Historical architecture relied on passive design approaches, such as the inclusion of sun shading to provide comfortable indoor conditions.

Since the second half of the 20th century, when technology became affordable and readily available, building design was able to rely on energy hungry devices, such as air conditioning and artificial lighting to provide the desired comfort.

With energy becoming more expensive and showing the effects on our environment,

Your encouraged to design buildings that thrive on passive design, rather than active appliances.

Did you know that external sun shading can be up to 5 times more effective than internal shading?

External shading devices protect the building envelope and reduce heat transfer through the building fabric. Whereas internal shading devices can reflect a small proportion of the heat that has already penetrated the buildings fabric.

Appropriately designed sun shading will not only support comfortable building temperatures but will help you save energy and money on cooling and heating systems.

Climate requires building facade design that responds to changing summer and winter temperatures and changing sun angles throughout the year.

Fixed or flexible external shading should protect your windows from unwanted heat gain in summer and allow for desired heat gain in winter.

The effectiveness of different shading devices is expressed as the Fc value, also called the shading factor.

It is measured in the proportion of solar energy entering a window. A low figure means the shading device is very effective, most of the solar energy is excluded.

A high figure means the shading device is not very effective, a lot of heat enters the room. A figure of 1 means no shading device is applied.

Refer to the example of internal and external louvres below:

Sun Angles

Different Facades Require Different External Shading

The graphic shows how sun angles change, depending on the season, the orientation, and time of the day.

Generally speaking, summer sun angles are high (up to 75°) and winter angles are considerably lower (up to 29°).

Furthermore, midday sun in the North is higher than morning or evening sun in the East and West.

North

Due to the sun’s high angle in summer, shading can be horizontal and fixed.

To provide full shading from late October to late February in Melbourne, the depth of the horizontal overhang should be approximately 45% of the vertical height to be shaded, measured from the window sill to the underside of the shading device.

This depth represents a good compromise between shading in summer and winter solar gain.

Fixed horizontal shading can be provided through structures, such as eaves, awnings, pergolas and verandas.

Adjustable external shading devices are also an option for north facing glazing, however they rely on the occupier understanding when to operate them for maximum benefit

East and West

Even in summer, eastern and western facades are exposed to relatively low sun angles.

On 21 December (mid-summer), eastern and western sun angles remain below 60°. Due to those low sun angles, normal fixed horizontal sun shading becomes ineffective.

Therefore adjustable shading devices are recommended.

These may include:

  • Canvas blinds (horizontal or vertical) ;
  • Conventional or roller shutters;
  • Angled metal or timber slats;
  • Shade cloth over pergolas.

The flexibility will allow occupants to respond to different seasons and individual comfort levels.

Furthermore, well designed flexible shading will contribute to a building’s architectural appearance and meet occupant’s privacy requirements.

South

For example in Australia (the opposite in the Northern Hemisphere), southern facades receive very little direct sunlight.

Only in midsummer will some low angled sun hit a southern facade, in the morning and evening.

Therefore it is not required to provide external shading devices.

However, when a building has an overheating problem, a flexible shading installation on the southwest can be an valuable addition.

Nevertheless, internal glare protection should be provided, especially for working environments.

Comparing Different External Shading Devices

“It is amazing what a difference the installation of external blinds made.

In summer we just keep them closed during the day, which means when coming home in the evening the house is still comfortably cool.

In the past we had to turn on the air conditioning units and wait at least half an hour before temperatures became comfortable.

Not to mention the electricity costs associated with relying on air-conditioning.”

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