Good underfloor heating (electric or water-borne) is an ideal heating method,
and underfloor heating combined with a wood floor gives optimal domestic
comfort.
The laying instructions for each floor type also apply when
laying over underfloor heating.
The following instructions summarise what is specific to wood floors laid over underfloor heating.
Special Requirements
The floor construction must have a heat distribution
layer that provides a very even temperature over the entire floor area, in order
to avoid localised excessively high temperatures.
The whole floor area must be heated. However, this does not apply
with comfortheating systems, which complement ordinary heating. The temperature
with these systems is considerably lower than the permitted maximum of
27°C.
The floor covering must have a low resistance to thermal
transmittance.
It must be possible to control and limit the surface temperature with great
accuracy.
The surface temperature of the finished floor must never exceed 27°C at any
point. This also applies under rugs, etc., and furniture. Provided that rugs are
not too thick, or there are not too many, a reasonable temperature for exposed
floor areas is 23°C, giving a room temperature of approx 21°C. This of course
assumes that the room has normal heating requirements and normal standards
of draught-proofing, insulation, window areas, etc.
A vapour barrier must be built into the floor construction, as close to the
wood floor as possible. If the joists are thick or heavy, it is particularly
important that the vapour barrier is close to the wood floor. The vapour barrier
must never be underneath the joist structure.
Ensure that there are no air gaps between the wood floor and the surface
beneath, as this could cause the wood to dry
out.
Choice of wood floor:
Ideal choices are Kährs 15 mm
multi-layer parquet floor or Kährs 7 mm Linnea, with the woodloc joint. This
reduces the risk of cracking.
Kährs parquet can be laid over underfloor
heating, which must distribute the heat efficiently and evenly across the
floor.
The surface temperature of the floor must never exceed 27°C. This
also applies near radiator pipes and under any rugs, etc.
Beech and Hard
Maple multi-layer parquet floors expand and contract more than other wood
species. Underfloor heating causes the wood to dry out more, which results in
additional shrinkage. In a cold, dry climate (e.g. in Sweden), cracks between
strips and slightly concave boards are to be
expected.
Installation:
The working temperature when laying
should be at least 18°C. This applies to boards, subfloor and the room air
temperature. Relative humidity (RH) of the air must be less than 60% before,
during and after laying the floor. Flooring paper should be the first choice as
the interlayer, because both expanded polythene foam and cork paper have a
higher resistance to thermal transmittance. Kährs multi-layer parquet or Kährs
Linnea with woodloc must not be glued.
Remember that a floor laid over underfloor heating is more
susceptible to moisture than an unheated floor, because of the greater
difference in floor's moisture ratios in its driest and most moist
states.
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