This article provides additional guidance on the Floor levels. It is important that all workmanship carried out during construction is completed in accordance with the relevant tolerances.
One might think this is pretty obvious, but a floor should be level! However once you take account of shrinkage, occasional poor workmanship and deflection; as with ‘flat roof’ designs, the difference between a designed level and actual level outcome can result in potential problems at completion stage.
Our Technical Manual makes reference to floor levels in Section 1 - Tolerances. It gives a recommendation that ‘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’.
Therefore, it is important when floors are constructed, particularly upper (intermediate) floors, that the setting out of the supporting elements to the floor (walls, beams etc.) is checked before the floor is put in position. Any ‘out of levelness’ that is built in at this stage will be still apparent when the floor boarding is installed, particularly in the case of timber floors. Shimming / packing should be avoided as these can also shrink or become loose.
On concrete floors, the levelness can be corrected to a degree with screeding, however, that should not result in the thickness of screed being below the recommended minimum thickness required to accommodate the out of ‘levelness’. For the purposes of this article, we are concentrating on providing guidance for upper floors (intermediate floors); however it can also be applicable to ground floors.
A high majority of upper floors in housing is still timber based and as stated above, shrinkage and poor workmanship can be a factor when finding a floor is ‘too much out of level’ post completion. However, another key factor is the Premier Guarantee warranty requirement for level of floors as stated in our Technical Manual Section 1 - Tolerances.
A floor joist (or in fact a concrete beam / plank) can be designed either by using TRADA Eurocode tables (timber joists) or by calculation to be within permissible deflection parameters following the British Standard or Euro code, but this may still exceed the maximum out of level requirement as found in section 1 of our Technical Manual.
For example, a timber floor joist spanning 4 metres between supports and is 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 1 metre intervals there could be a 6mm drop in level (per metre).
Although that amount is within design parameters under the BS, it would exceed the maximum out of level of 4mm per metre as required by Premier Guarantee tolerances as in the Technical Manual.
Our tolerances chapter is based on ‘Industry standards’ within the warranty sector, so Designers and Engineers must take this in to account at the design stage.
‘Technical Manual - Section 10: Upper Floors’ also makes reference to the fact that although an upper floor may be in accordance with a design to a BS or Eurocode Standard for deflection; the floor must be within the tolerances defined in Section 1 of the Technical Manual.
It’s not just timber floors this tolerance standard applies too. Concrete beam and block floors should also meet this requirement.
With all upper floors, deflection can also impact on the floor finishes, in particularly rigid finishes such as ceramic tiling, which may not be able to tolerate the ‘permissible deflection’ parameters.
For our Warranty purposes:
Designers and Engineers must be made aware of our Tolerances, 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 within our ‘Defects Insurance period’. This is applicable to buildings covered under the New Homes, Social Housing and Private residential policies.
Please Note: Every care was taken to ensure the information in this article was correct at the time of publication. Any written guidance provided does not replace the reader’s professional judgement and any construction project should comply with the relevant Building Regulations or applicable technical standards. However, for the most up to date Premier Guarantee technical guidance please refer to your Risk Management Surveyor and the latest version of the Premier Guarantee Technical Manual.