Muller Design Ltd -

Sub-floors
The following information contains industry standard tolerances for the preparation of sub-floors that are to be covered with wood flooring. Cement Screed Screed must measure level +/- 3mm per 2 linear metres in all directions. It must have a maximum moisture level of 4% and a relative humidity (ERH) of less than 75% when tested with a BS 8203 hygrometer. Hygrometer testing involves 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. Fast dry and rapid set screed and self- levelling products can accelerate the time taken to achieve the correct moisture levels. If a damp proof membrane is not incorporated within concrete slabs or screeds a surface DPM must be used. Joists Either a chipboard or plywood sub-floor must be fixed to the joists and measure level +/- 3mm per 2 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 floated 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 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. 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 should 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 2% 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 it’s 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. 18C should be maintained throughout the installation period and for a minimum of 24 hours thereafter. Under-floor heating must be switched off immediately in areas where floor protection is fitted, as soon as it is fitted, and only re-activated when the floor protection is removed. Post installation environment requirements The recommended humidity level is 50% it should not be allowed to fall below 40% or rise above 60%, programmable humidifiers or vaporizers are recommended. The surface temperature of the floor should never be below 10C or above 27C, heating systems can be programmed to remain within these parameters.

Sub-floors

The following information contains industry standard tolerances for the preparation of sub-floors that are to be covered with wood flooring.

Cement Screed
Screed must measure level +/- 3mm per 2 linear metres in all directions. It must have a maximum moisture level of 4% and a relative humidity (ERH) of less than 75% when tested with a BS 8203 hygrometer.
Hygrometer testing involves 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.
Fast dry and rapid set screed and self- levelling products can accelerate the time taken to achieve the correct moisture levels.
If a damp proof membrane is not incorporated within concrete slabs or screeds a surface DPM must be used.

Joists
Either a chipboard or plywood sub-floor must be fixed to the joists and measure level +/- 3mm per 2 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 floated 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
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.

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 should 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 2% 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 it’s 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.
18C should be maintained throughout the installation period and for a minimum of 24 hours thereafter.
Under-floor heating must be switched off immediately in areas where floor protection is fitted, as soon as it is fitted, and only re-activated when the floor protection is removed.

Post installation environment requirements
The recommended humidity level is 50% it should not be allowed to fall below 40% or rise above 60%, programmable humidifiers or vaporizers are recommended.
The surface temperature of the floor should never be below 10C or above 27C, heating systems can be programmed to remain within these parameters.