External Shading Devices
What are they?
External shading can either take the form of:
- External solid or perforated shade devices such as panels mounted on the outside of the building. Shades may be static or movable (typically under automatic control).
- Reflective film that can be applied to glazing; or
- ‘Fritting’, which is architectural glazing with an applied opaque pattern.
They all act by deflecting the sun’s rays from the building glazing, thereby reducing solar gain within the occupied space.
Advantages / Disadvantages
- Reduces the need for air conditioning
- Considerably more effective at reducing solar gain than internal blinds.
- Higher cost to retrofit than internal blinds.
- Reduces natural light and therefore increases the need for artificial lighting.
- Can impact on occupant views.
External shading devices reduce the cooling requirement in a building, therefore saving energy. The effectiveness of the shading depends on building form, the shading design and the amount and orientation of glazing.
External shading will add to the cost of cleaning the external façade. Maintenance costs will be higher if the shading is automated because there are moving parts that require periodic overhaul and adjustment.
Some shading systems may also make it difficult to clean the building’s windows, and may also attract birdlife and the associated droppings.
Solar film has a short lifespan (5 years) if applied to the exterior of the glass, but is more effective in that location. When installed on the interior face of the glass, it will be less effective but has a much longer lifespan (15 years)
Retrofit / improvement opportunities
External shading devices are technically challenging to retrofit depending on the type of building façade. For example, glazed curtain walling does not readily allow sufficient fixing points to allow installation. It can also be difficult to retrofit from a planning perspective because the external appearance of the building will be affected. Adding external shading to an existing building is typically undertaken as part of any façade modernisation works.
Solar film does not typically require planning approval unless it alters the external appearance of the building or the building is listed or in a conservation area.
All building types.
Temperature control / Occupant comfort
External shading devised will improve temperature control and comfort if positioned effectively, but will reduce the amount of natural light entering a space.
External shading devices most typically comprise fins or a louvre system on the external face of the building – either a fixed system or automatically adjustable depending on sunlight levels.
Window films are difficult to see when but close inspection often reveals small lines around the edge of the window pane where the film has not covered.
Fritting is visible as opaque elements within the glass itself.
Questions to ask
- Is the shading system fixed or automatically controlled?
- Is the window film applied to the interior or exterior of the glass?
Carbon Trust How to implement solar shading (CTL065)
CIBSE TM37 Design for Improved Solar