Floor Flatness and Levelness in Building Construction

What is floor flatness and levelness?

Pertaining to the surface’s smoothness floor flatness and levelness is a measurement of how smooth or level a floor is. Floor flatness is measure of smoothness of one surface while floor levelness is about uniformity of the very same surface.

Floor Flatness and Levelness in Construction

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It intends to be the foundation upon which the aesthetics, functionality, and longevity of a structure rest. Typically measured using a straightedge or an instrument called a levelometer, it is later compared to a specified tolerance in the building plan. Traditionally, it was measured over a 2-foot square area.

It acts as the groundwork for a structure’s integrity in building construction. It ensures smoothness, stability, and safety within a built environment.

There are various benefits associated with achieving optimal floor flatness, some of them are:

  • A flat floor surface ensures safety, reducing the risk of trips. This minimizes the liability of the building owner and provides a safer environment for them. 
  • The visual appeal of the space is enhanced with smooth and even It creates an inviting environment, contributing to a positive first impression. 
  • The lifespan of the flooring gets prolonged when it is maintained properly. Immediate attention to issues can minimize the worsening of cases and increase the longevity of the functionality and appearance of the structure.

Factors affecting Floor flatness

There are several factors that influence the floor flatness in building construction, including. These factors can impact the overall quality and levelness of a floor surface. Some key factors include –  

  • Concrete mix design: The type of the concrete mix and its consistency impact the final 
  • Curing process: Improper curing results in moisture and temperature control, leading to cracks and 
  • Substrate preparation: An uneven subgrade can lead to uneven 
  • Slab placement and floor finishing: Techniques used to lay the concrete slab impact the final 

Methods of testing floor flatness and levelness

Methods of testing floor flatness and levelness

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Measuring floor flatness and levelness is very essential to ensuring the structural integrity of the building. There are varied ways to measure floor flatness/levelness reporting and survey. Let us explore them one-by-one.  

Traditional methods

The traditional method used to measure floor flatness, like using a straightedge and level, has been utilized for centuries now. With these methods, workers manually assess the flatness of a surface. This assessment was limited due to human errors and the inability to detect irregularities, making it somewhat rudimentary in its accuracy. 

Some examples of traditional methods are:  

  • String and Straightedge: To measure variances, generally string and straightedge are being utilized in this approach.  
  • Handheld levels: Employees utilize handheld levels to check for levelness by looking at bubbles.  
  • Visual inspection: A subjective evaluation, it is about relying on workers with experience in visual inspection. 

Modern techniques

Discussing modern techniques, laser leveling and digital instruments have revolutionized the way of measuring. With laser leveling, a laser beam is projected into the floor surface, and variations are detected, thereby eliminating human errors and offering precise measurement.

Digital instruments, on the other hand, like electronic levels and inclinometers, further enhance the accuracy rate by providing digital readouts.

However, out of all, a laser scanner or 3D scanning principles is the best bet to deploy for these purposes. Read out our detail blog on how laser scanning could be useful for floor flatness/levelness testing and reporting.  

Some examples of modern techniques are:  

  • Laser leveling: The laser leveling process uses sensors and laser beams to effectively get the most accurate reading out of the floor’s situation.  
  • Digital floor profilers: Advanced sensors and algorithms provide comprehensive profiles with digital floor profilers.  
  • Floor scanning: Also, 3D scanning for floor flatness and levelness is used to gather millions of data points and then subsequently for heatmap generation and modeling.  

Floor flatness and levelness reporting

After testing, a report is being prepared on the test outcomes. A typical floor flatness and levelness report includes –  

  • A description of the test surface 
  • Test sections  
  • Location of test runs 
  • Overall FF and FL numbers for the slab 
  • The individual FF and FL numbers for each test run 
  • And whether any required local minimum was violated.  

Prior to analyzing a report, make sure that the total FF and FL numbers satisfy the necessary standards.

Let’s say the project specifications stipulate a minimum FF of 25 and a minimum FL of 20. The specification should provide the equivalent minimum local values, which are normally 60% of these values, or 15.0 and 12.0, respectively.  

Understanding F number system

Understanding floor flatness numbers

While talking about various techniques, let’s delve into the F-number system to understand how it works for testing floor flatness and levelness. The F-number system adds a quantitative aspect, assigning numerical values to different floor flatness and levelness. A higher F-number represents a flatter a more uniform sruface, while a lower one indicates a decreased deviation from a perfectly flat or uniform surface.

To understand the F-number system completely, you have to be comprehensible of three F numbers i.e., FF, FL, or FT  

FF number (Floor flatness number)

How near the floor is to being planar, is represented by FF values. Stated differently, floor flatness is a statistical measure of how uneven or wavy a concrete floor is, accounting for both wave height (amplitude) and horizontal spacing between waves (wavelength).

After the concrete is laid, elevation differences are measured every foot for 72 hours, and the FF measurement is calculated using a formula. The measures are linear, with greater values denoting a floor that is flatter. A floor having an FF number/measurement of 60, for instance, is twice as flat as one having an F measurement of 30. 

FL number (Floor levelness number) 

FL numbers give information regarding the levelness of the concrete floor. The degree to which the completed floor resembles the desired slope specified in the design documentation is referred to as levelness.

Within 72 hours of the concrete being put, elevation deviations are measured every 10 feet, and the results are incorporated into a formula to calculate floor levelness (FL).

Since the FL values are linear, a floor with FL of 50 is twice as level as one with a FL of 25. Higher FL numbers denote a more level floor. 

And the last is FT (Floor tolerance)  

The permissible range of departure from a given norm for flatness and levelness across the floor surface is determined by floor tolerance.

Here is a floor flatness and levelness chart for optimal value in different use cases

floor flatness and levelness chart for optimal value

Achieving floor flatness and levelness

Achieving and maintaining floor flatness and levelness is a continuous process involving a lot of detailing during the construction process. During the construction phase, proper techniques need to be utilized along with the right tools to achieve optimal value of flatness in your floor.

This process involves a thorough preparation of the surface and the utilization of good-quality materials and skilled labor. Advanced equipment helps to achieve precise leveling and finishing, reducing the risk of deviations and ensuring uniformity across the surface. 

Maintaining its longevity plays a pivotal role. After the construction, preserving the surface involves routine care and looking after any after-care of the surface.

Addressing issues promptly prevents the worsening of cases and helps maintain the longevity of the floor. 

  • Assessment: Look for high areas, dips, and unevenness in the floor. Follow a quantitive approach by testing.  
  • Cleaning: To ensure optimal adherence, clean any dust, spot, grease, and debris completely for optimal working in later stages.  
  • Floor Preparation: Use the appropriate filler to seal cracks, holes, and gaps, then let it cure and wait for some time.  
  • Priming: For better uniformity and adherence, use primer. The purpose of primer is to ensure prevention of rapid drying of floors.  
  • Mixing Leveling Compound: For mixing compound, refer to the manufacturer’s instructions. 
  • Apply Leveling Compound: Fill up low areas by uniformly pouring and spreading the compound. 
  • Smoothing and Finishing: To create a level, smooth surface, use tools. Some of the suitable concrete tools would be Trowel, Screed, Edger, etc.  
  • Drying and Curing: Give the compound the time it needs to dry, usually a few hours to several days. 
  • Surface preparation: Before installing flooring, prepare the surface by sweeping, vacuuming, or sanding any blemishes. 
  • Installation of Flooring: Install the selected flooring material in accordance with the manufacturer’s instructions. 


Floor flatness and levelness might seem like a very minor detail in a huge structure, but it has far bigger impacts in the long run. It is important to prioritize the maintenance and repair of flooring whenever deemed necessary. Architects and builders not only design spaces that look aesthetically appealing but also keep safety in mind to ensure the long-term satisfaction of the owners. 

Further Reading

Would you like to explore laser scanning services for faster, more accurate floor data in building construction?