Note Horizontal and Vertical Datum Grading Plan Drawing

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Datum

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On a construction projection, a datum level is an capricious horizontal aeroplane of reference from which all vertical dimensions are measured. It can show the vertical tiptop divergence between floor levels of a building as well as differences in levels between 1 function of the site and some other.

The datum on a site can be given a 0.000m designation just this does not have to necessarily be outside ground level; if it is, a ground flooring may be at say, 0.750m and a outset floor at 4.750 and and so on proceeding up the building. In contrast, a basement which volition exist beneath ground will be beneath datum level and will therefore have a minus symbol prefixed to it e.g -3.250m.

Nonetheless, minus signs tin be easily misread, not seen or read every bit a nuance, then can crusade defoliation. For this reason, a suitable fixed point (called a temporary criterion – TBM) is assumed to ensure that all other levels are positive. So, in the case of the basement level referred to above, information technology may be given 0.000m as the site datum, in which case (following the logic from higher up) footing level = three.250m; ground floor = 4.000m; first flooring = viii.000m and then on. The levels normally refer to finished floor levels (FFL) only can too point other features east.g finished structural level (FSL)

Datum levels are useful equally they provide points of reference to allow the vertical setting out of buildings and how they chronicle to other levels on a site. They should be conspicuously indicated on all relevant drawings with all levels described in metres to three decimal places merely always equally positive numbers considering they are above datum level.

It is increasingly the case, especially for big projects, that the Ordnance Survey (Os) datum is used as a project datum every bit information technology allows piece of work on the site to be related to other features in the expanse, e.k manholes and sewers, local gradients etc. Using this approach means that everything is to the aforementioned OS datum and Bone grid (OSG).

Note: OS datum is taken as superlative above sea-level based on a known datum indicate at Newlyn, Cornwall; if the OS datum is being used, it must be indicated on the drawings. OSG is the standard known grid beyond the United kingdom of great britain and northern ireland.

For more information see: Ordnance datum.

[edit] Other datums

A datum may besides be a line from which all other horizontal dimensions relate to whether, on architectural or technology drawings. An example is a building that has a programme generated from a dorsum wall.

A datum may also be a betoken that is used for setting out the edifice. This must be clearly marked on drawings to help the contractor'south setting out. For example, a circular building will be set out from a datum point from which all radii are generated.

Drawing for Understanding, Creating Interpretive Drawings of Celebrated Buildings, published by Historic England in 2016 defines a datum line equally: 'A horizontal or vertical reference line used to control height and horizontal distance measurements.'

[edit] Related articles on Designing Buildings

• At grade.
• Data.
• Ordnance Survey.
• Origin point.
• Geographic information system GIS.
• Global positioning systems and global navigation satellite systems.
• Building height.
• International Holding Measurement Standards.
• Invert.
• Location program.
• Measurement.
• Ordnance datum.
• Setting out.
• Site plan.
• Water engineering.

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Source: https://www.designingbuildings.co.uk/wiki/Datum

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