An underlay is a layer of material or cushioning which is laid between a wooden floor or carpet and the subfloor. It acts as a barrier to reduce dust particles, drafts, heat loss and sound. The tog rating measures the thermal resistance of the underlay. The higher the tog, the better the underlay is for warmth as it provides an extra layer of insulation. The colour or thickness of an underlay does not make any difference to thermal resistance so if an underlay is very thick but does not have a tog rating then it is not guaranteed to provide insulation against heat loss.
If underfloor heating is being used then the underlay should be suitable for use with the underfloor heating product and therefore have a low tog rating such as 0.35 tog. This is because the heat needs to be transferred from the underfloor heating system to the chosen floor covering, so the least thermal resistance is needed. Therefore a lower tog rating will provide a better performance for your underfloor heating system.
Quick Guide to tog ratings
Different floor coverings require different types of underlay with different tog ratings:
-
Type of floor covering
Recommended underlay tog rating
Hardwood Flooring
1.0 tog
Carpets
Over 2.5 tog
Underfloor Heating
Underlays should not be used to level an uneven subfloor, or provide a barrier to moisture. Separate products such as a floor levelling compound and Damp Proof Membranes (DPM) are available for these jobs.
