Privacy Screens and Wind loads
As a glass railing and balustrade manufacturer and supplier we run into frequent requests by customers for what is known as a “Privacy screen”.
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“Privacy screens” are what is often requested by local authorities. This is stipulated by them if your terrace, balcony or part of them only overlooks a neighbour’s property. It is requested so that your use of this balcony area does not invade or compromise their privacy.
Privacy screens are usually requested to be 1.8m high and use a glass that cannot be seen through – i.e. an opaque glass.
The subject of privacy screens and their height requires extra consideration for wind loadings and the subject of wind loading is not a simple calculation as there are many variables that need to be considered.
The loads on privacy screens are a lot larger than on regular glass balcony rails and will require stronger posts with bigger base plates.
Therefore the structural design of 1.8m high screens is governed by wind loading. For sites in the UK wind loading is calculated in accordance with British Standard 6399-2: 1997 Code of practice for wind loads. The basic wind speed for different geographical locations is obtained from Figure 6 of BS 6399. The basic wind speed varies from 20m/sec in an area around Oxford to 30m/sec in the North Scottish Islands.
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The basic wind speed is adjusted by various factors to allow for differences in site conditions. These include the site altitude and topography, whether the site is in a town or in the country, distance from the sea, and height of the building.
Special base plates and posts have been developed by us to be able to meet the required loads. In accordance with all the required parameters the spacing of the vertical posts is varied to suit different wind load conditions.
We have created three post spacings (1.0m, 1.25m & 1.5m post centres) to meet three design criteria. Should a site fall outside the standard design criteria, individual site specific designs can be prepared as required. These are summed up in three clear structural calculations available upon request.
Things to ascertain:
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The area the job is in in terms of basic wind speed. On each calculation there is a map of the UK with basic wind speeds (figure 6 on p3).
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Altitude of site
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Effective height of the building
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Site distance from the sea.
It is essential to read the reports but the main differences and parameter variation of the three calculations are:
For post spacings of 1.5m
For sites at an altitude of 50 metres or less above sea level within the 23 m/sec basic wind speed area, examples of the different types of terrain and height of buildings for which this system is suitable are as follows:
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Any coastal, country, or town location where the effective building height is 9 metres or less.
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Sites in town or country areas 10 km or more from the sea where the effective building height is 12 metres or less.
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Town sites 100 km or more from the sea, with an effective building height of 19m or less.
For post spacings of 1.2m
For sites at an altitude of 100 metres or less above sea level within the 25 m/sec basic wind speed area, examples of the different types of terrain and height of buildings for which this system is suitable are as follows:
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Any coastal, country, or town location where the effective building height is 7 metres or less.
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Sites in town or country areas 10 km or more from the sea where the effective building height is 8 metres or less.
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Town sites 100 km or more from the sea, with an effective building height of 14m or less.
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For post spacings of 1.0m
For sites at an altitude of 100 metres or less above sea level within the 25 m/sec basic wind speed area, examples of the different types of terrain and height of buildings for which this system is suitable are as follows:
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Any coastal, country, or town location where the effective building height is 19 metres or less.
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Sites in town or country areas 10 km or more from the sea where the effective building height is 20 metres or less.
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Town sites 100 km or more from the sea, with an effective building height of 30m or less.
The closer the post spacing the larger the load that can be applied.
The subject of privacy screen, their required loads and aesthetics are an intricate subject that needs to be properly assessed before designing a solution.