It goes without saying floors should be level.

However, once you've taken into account movement, deflection and different materials this can be easier said than done.

So, how much deflection is acceptable and how do you make your floors as flat as possible?

What can cause the floor to be out of level?

When finding a floor is out of level after completion, it is often the result of shrinkage, poor workmanship and deflection. Shimming or packing (materials used to fill gaps or make something level) can also shrink or become loose.

A floor joist can be designed to be within permissible deflection parameters under British Standard or Euro code, but may still exceed the maximum out of level requirement as found in Chapter 1 of our Technical Manual.

For example, a timber floor joist spanning 4m between supports and provided with solid strutting can, if designed to BS 5268 have a maximum permissible deflection of 12mm. So at mid span (2m) there ‘could be’ 12mm out of level and potentially at 1m intervals there could be a 6mm drop in level (per metre).

Although that amount is within design parameters under the British Standard, it would exceed the maximum out of level of 4mm per metre as required by our Technical Manual.

Tips for achieving a level floor

Designers and Structural Engineers must take into account at the design stage that the floor must be within the tolerances set out in Chapter 1 of our Technical Manual, as although the floor joist design may meet a relevant code or standard for deflection, it could result in a potential claim of exceeding the maximum out of level requirements as a defect of the Technical Manual.

Our Technical Manual Chapter 1.4 recommends floors up to 6m across can be a maximum of 4mm out of level per metre and a maximum of 25mm overall for larger spans.

It’s not just timber floors this tolerance standard applies too. Concrete beam and block floors should also meet this requirement.

To ensure the finished floor is level and within permissible tolerances our advice is to check, check and check again! When constructing upper floors any supporting walls or beams that are out of level will be reflected in the final floor, particularly when it comes to timber floors. So checking these before the floor is put in position will save time and effort later on.

By Frzana Ferguson