According to British Standards, Surface Regularity is defined as the deviation in height of the surface of a flooring layer over short distances in a local area. In simpler terms, it is the ‘flatness’ or ‘measure of waviness’ of the screeded surface.
To facilitate easy assessment of the flatness of the floor screed, the extent of surface regularity of the screed is generally expressed in terms of permissible departure from the underside of a 2m straightedge on legs laid in contact with the screed.
|Class||Maximum Permissible Departure from a 2m Straight Edge (mm)||Application|
|SR1||3mm||High standard floors, for special use|
|SR2||5mm||Normal standard floors, for use in commercial and industrial buildings|
|SR3||10mm||Utility standard floors, where surface regularity is less critical|
At CSC, we generally install floor screeds to SR2 specification. We also cater to projects that require SR1. However, it should be noted that SR1 specifications usually dictate a higher cost structure, as is documented in BS8204.
Departure from Datum
Departure from Datum is another important aspect which is often confused with surface regularity. Unlike Surface Regularity, departure from datum is the maximum permissible deviation of the finished surface of the flooring from datum, considering the extent of area of the floor and its intended use. The departure from datum can usually go up to +/-15 mm for large areas.
It is sometimes seen that the M10 specifications produced by architects are merely reproductions from historical projects, which quite often fail to describe the requirements in an entirely correct manner, which ultimately results in incorrect specifications for the departure from datum, SR requirement, BRE category, construction type, etc. It is therefore important that, depending on the area of the floor and its intended use, the designer should specify the expected departure from datum in advance.