Floor requirements to provide thermal mass for heating
A concrete slab floor provides excellent thermal mass. For maximum heat absorption, the surface
should:
• be exposed or be covered with a high density material such as tile or slate
• have a dark colour or a textured or matt finish
• be 100–200 mm thick
• be insulated underneath the slab (to give an R-value of at least 1.9) so that heat moves up into the
interior space rather than into the ground
• have slab edge insulation to reduce heat loss from the slab perimeter to the outside air.
Materials with high thermal resistance (such as carpet, cork or timber) should never be laid over
concrete floors that are to provide thermal mass.
Suspended concrete upper floors in two-storey construction may be used effectively as thermal mass. By
leaving the underside of the floor exposed, radiated heat will move to both the upper and the lower
levels.