Nationwide Floor Screeding

Datum Level – Exactly What Is It?
Essential in construction

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About Datum Level

Interior Screed Group Ltd are a nationwide floor screeding installer specialising in all types of floor screeding systems. We work with the biggest and most prestigious names in the residential and commercial building sectors.

What is a Datum Level on a construction site?

Datum Level is an horizontal plane on a construction site used to determine all other vertical dimensions to be measured from it. Datum level highlight’s differentials between vertical heights of floor levels along with differing levels of two separate points on the site.
As is often the case Datum Level is given a 0.000m designation (though this doesn’t have to be the ground level outside; the ground floor could be 0.650m with a first floor at 4.650m for example. A basement would be below the Datum Level so would be shown as a minus number, - 2.950m for example.
It is not uncommon, however, for the minus sign to be missed or misrepresented (as a dash for example) so often a temporary benchmark (TBM: a fixed point) is used so all over levels (even subterraneous) are represented by a positive value. Looking at the example above, the value assigned to the Datum Level (0.000m) would be assigned to the basement and the levels above would be adjusted accordingly.

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Datum levels give points of reference to enable the vertical setting out of the building by a site engineer; clearly indicated on all site drawings datum level is determined in metres in terms of a unit of measure. Datum level is indicated to three decimal places and because it is the building being set out the numbers should all be positive. The OS datum is the height above sea level and pertains to a specific datum point at Newlyn which is in Cornwall. If you are using the OS datum it must be clearly demarcated on your drawings.​ In particular with larger-scale developments, the Ordnance Survey (OS) datum is used as the Datum Level for the project/site. There are several advantages with this:
  • Work on the site can be related to other buildings and hard landscaping features like
  • You can take into account local gradients.
  • If you use the OS datum it is immediately compatible with the OD grid.
The Essential Guide to Floor Screeding Mixing Machines

Datum Level and Screed

British standards allow for a maximum departure from Datum of 15mm for floor screeding. In terms of SR (Surface Regularity) SR2 is normally specified as a standard measure and is plus or minus 5mm over a 2-meter straight edge.
Datum Levels are so critical to every building project. They are the reference point for every type of building work and are absolutely crucial in getting things right the first time. Measure once, screed once! Contact us for any help or advice on your construction project.