Preparation of the subfloors will depend on the condition of the existing structure and chosen method of floor installation. Before any installation takes place it is essential to determine the condition and moisture content of the subfloors.


Subfloor level should have no more than 3mm deviation with measuring over a 2 metre distance. The subfloor must conform to BS 8204: Part 1 1987, which states that it must not deviate by more than +/- 3mm under a 3mm straight edge in any one direction. Failure to keep to these tolerances may result in the floor squeaking or deflection of the floor in service.


Subfloors must also be vacuum clean, smooth and free of any debris, staples, visible nails, old adhesives or other dried substances before installation.


Timber Subfloors:

Wooden subfloors usually consist of pine floorboards or wood panel sheeting like plywood, chipboard etc. laid over joists or battens as a suspended floor. Prior to any installation the installer should check to see if the materials used are adequate and there is no water, moisture or rot present. A hydrometer reading should be used to see if the conditions are suitable and no damp is present.


Moisture content of the timber subfloor should be no more than 4% above or below the finished flooring. If the floor is on or below ground level the installer should also make sure there is adequate ventilation beneath and between the joists and air bricks are present and not blocked.


In the event that the timber subfloor is not fit for purpose or the work involves the construction of a new subfloor, the installer should use a minimum of 18mm thick External Grade Plywood or OSB Boards directly on the joists.


If the existing subfloor is adequate but not level, for example old uneven pine floorboards, a 12mm minimum External Grade Plywood or OSB Board can be glued directly on top of the existing subfloor. Where new sheeting is installed over an existing subfloor, any loose floorboards or boarding should be screwed down using long enough screws to penetrate and hold into the joists.


Concrete Subfloors:

The main responsibility of the installer prior to installation is making sure the moisture levels within the subfloor are low enough to lay the floor. Where concrete or other cementitious slabs are present, mainly in ground/basement levels, the installers should take a hygrometer reading to see if conditions are suitable and no damp is present. Screed or concrete subfloors must have under 4% moisture content. Failure to maintain these conditions could cause excessive dimensional change resulting in problems like delaminating, cupping, cracking, etc.


In addition to checking the moisture, in ground/basement levels the installer should check to see if a Damp Proof Membrane (DPM) exists and if not or if it has been compromised it is important that a new DPM is fitted before moving on to installing the floor.


If you have any further questions or would like to discuss in further detail installations and subfloors, please contact us on 0114 2581256
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