Buy & construct a wood floor

Dane Care are familiar with the work of a great many of the wood floor profession. You may have only taken supply of wood or had a particular company supply & fit, but often its a benefit to have a 3rd party to advise on getting even more from your wood floor. Using established relationships with wood and finish suppliers we can shed light on what is worrying you and help to complete anything that is going to be of further benefit.

Successful surface finishing relies on a stable, well constructed floor so if you have simply bought a floor then ensure your installer is thoroughly familiarise with the floor supplier’s installation guidance before works proceed.

Quality is, however, often undermined by the effects of the sub-floor structure. To this end, we provide guidance here on sub-floor industry standards. These should help a client understand and support the installer in pressing the main contractor to meet these requirements that constitute such an important aspect of the works.

1. Sub-floor Preparation

Cement Screed

Screed must measure level +/- 3mm per 3 linear metres in all directions. Surface moisture meters should be showing a maximum moisture level of 4%, whereupon a relative humidity (ERH) of less than 75% must be recorded with a BS 8203 hygrometer prior to the installation of the wood floor. Hygrometer testing is preferably undertaken by drilling into the screed. The screed must be marked to allow for invasive testing without damage to pipes, electrical wiring, or membranes within the screed. Plugs can be supplied to builders for insertion during the screed build so they are ready for later testing without risking any sub-floor structure. Should insertion of plugs be impossible then use of a surface box for hygrometer testing will be undertaken.

When self-levelling has been used over concrete then, whilst other methods of moisture readings may be used to monitor the progress of a screed’s drying, the drilling in of plugs for a Hygrometer test is the only absolute test, since it prevents surface self-levelling products from masking the true moisture of an underlying screed. It should be noted that use of self-levelling compounds BEFORE the screed is known to be dry is incorrect, since they significantly set back the drying schedule for the screed. Seek advice in advance from your building products suppliers.


A contractor cannot install onto joists and continue to offer an installation guarantee. Joists, existing or new, move and that will mean wood floors may squeak!

Either a chipboard or plywood sub-floor must be fixed to the joists and measure level +/- 3mm per 3 linear metres in all directions.

Chipboard must be tongue and grooved and have a minimum thickness of 18mm. It must be glued at the tongue and groove and screwed to the joists at 300mm centres. The joints must be staggered.

Plywood must have a minimum thickness of 12.5mm for a fixed wood floor, 18mm for a glued wood floor and 18mm for under-floor heating. The plywood must be screwed to the joists at 300mm centres. The joints must be staggered.


Floorboards above joists must measure level +/- 3mm per 2 linear metres in all directions. They must be fixed with 2 screws per board at each joist fixing point. Any damaged or rotten boards must be replaced. Only fit wood-floors over floorboards if the grain runs at 90 degrees to the original floorboard direction and glue is used. This constraint will over-ride any design requirements.

Underfloor Heating

For installation of wood floors above under-floor heating the same sub-floor preparation as already outlined for screed and joist supported sub-floors is correct.

Cement screeds, screed repairs and screed leveling materials must however be approved by the under-floor heating manufacturer.

The sub-floor support material must be satisfactorily secured and fixed above the heating system.

Operation of all underfloor heating systems prior to wood floor installation

The heating system must be activated and the temperature increased in daily increments of 5C, ie. day one 5C, day two 10C, day three 15C until the maximum temperature is reached.

The maximum temperature should be maintained for at least 48 hours or in the case of cement screed, until the correct moisture level of 4% and relative humidity (ERH) of less than 75% is achieved and recorded.

The heating system should then be cooled observing the same 5C adjustments per day.

When the heating system has returned to its lowest level switch the heating system off for 2 days.

Re-activate the heating system and once again increase the temperature by 5C per day until the installation temperature of 18C is reached.

This effectively means that a 15 day period is required after the start-up of your boiler or electrics and the start of your floor installation. This assumes the screed is dry before this period.

Installation environment requirements

18C should be maintained throughout the installation period and for a minimum of 24 hours thereafter.

The recommended humidity level is 50% it should not be allowed to fall below 40% or rise above 60%.