Floor Flatness

Level Tolerances & Floor Surface Regularity

It is a known fact in construction that floors need to be flat, not level. Flatness is the requirement.

Datum or Floor Flatness:

The maximum permissible departure from the level of a dappled finished self-levelling screed floor from a specified or agreed datum plane should consider the area of the floor and its end use.

For large areas, for ordinary purposes, a departure of up to 10 mm from the datum is generally considered to be satisfactory. Greater accuracy to the datum can be necessary for small rooms or for low-level glazing where a glazing bar (UK) muntin (US) meets the floor screed where the design for low-level glazing is specified or in the vicinity of door openings and where specialized equipment is to be installed directly on the floor.

Surface regularity is an essential quality of a screed or floor surface, often described as a measure of the waviness of the surface.

Tolerances on a Level & Floor Surface Regularity

Given below is the general surface regularity classification for regular accuracy floors surface.

Surface Regularity or Class SR: Maximum permissible departure from a 3m straight edge resting in contact with the floor.

Maximum gap measured with a slip gauge

Application SR1: 3 mm tolerances Standard for fine vinyl floor type surfaces


SR1 is a very smooth surface finish required for very fine floor covering. This cannot be achieved when pouring dappled finished class 2/3 floor. This is achieved usually by fine floor levelling an SR2/SR3 floor – customarily carried out by the fitter/installer of the fine floor covering.

SR 2:  5 mm Normal Standard for tile or timber

SR 3: 10 mm Utility Standard for tile or timber 

Remedial Measures in case of Non-Compliance

Remedial measures in non-compliance generally include localized grinding (where the effect on appearance is not an issue). The most feasible option would be localized grinding or the application of smoothing compounds. For cases where the screed is too high, removing and replacing the affected area might be necessary.

However, before resorting to any major remedial measures, it is best to compare the degree of non-compliance and its effect on the final flooring against the possible costs, delays, and impact on the floor’s appearance and long-term life.