Threshold
A threshold is a strip of wood, stone metal and so on that forms the bottom of a doorway, which is crossed when in entering a building or a room. It is sometimes referred to as a door sill or door saddle.
Thresholds can pose a barrier to passage for people with disabilities, and so thresholds are now typically level, rather than stepped, with a level or ramped approach. However, this can create difficulties preventing water penetration or air infiltration through a doorway from the outside, and so modern threshold designs can be complex.
An ‘accessible threshold’ is defined as a threshold that is level or, if it is raised, has a total height of not more than 15mm, a minimum number of upstands and slopes and with any upstands higher than 5mm chamfered.
Other acceptable solutions are described in ‘Accessible thresholds in new housing – Guidance for house builders and developers’, The Stationery Office Ltd. 1999.
Ref Approved document M, Volume 1: Dwellings.
The word threshold can also refer to a level at which a change applies, for example; the payroll threshold above which the apprenticeship levy applies, a size of project above which an Environmental Impact Assessment might be required, the threshold for appointment of principal contractors and principal designers, the temperature threshold above which overheating might occur and so on.
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