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Last edited 16 May 2022
Floor level (FL)
Finished Floor Level (FFL) is a planning and setting out term used in the design and construction of buildings, it may sometimes appear shortened to FFL on planning, layout and technical drawings. As it suggests, it indicates the intended level a floor should be at once finished ie once all the different sundry items are installed, for example insulation, screed, underlay and carpet.
Structural Floor Level (SFL) or sometimes Structural Slab Level (SSL) in the case of concrete frame buildings, describes the floor level prior to the addition of finishing items such as screed, underlay and flooring. The numerical measure will normally be written next to the abbreviation on a drawing often with a + to indicate vertical increase or - in the case of basements. The figure will be a certain amount above or below whatever the agreed setting out position or datum is. For example the setting out position might be 0.00, the SSL +3.0 and the FFL +3.3.
Building Ground Level (BGL) might be used to describe the setting out position for the building ie the 0.00 from which all other levels will be measured. The height of this in relationship to the site itself will depend on the approach taken and agreed by the project team, though it will normally be slightly higher than the Ordinace Survey (OS) Level or Natural Ground Level (NGL) to allow for structural foundations.
Ordinance Survey (OS) level, is based on the accepted levels or measures of the lay of land across the United Kingdom, these are calculated through the use of Ordnance Survey Bench marks (BMs) which are survey marks that are made by Ordnance Survey to record the height of the landscape above Ordnance Datum. Based on these and the process of surveying, the more localised OS or what might be call Natural Ground Levels are calculated and recorded.
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