GS, Oxford
Heat is lost through wooden floors either by conduction (wood is not a good insulator) or because of draughts through the joints. Your options are restricted if boards can’t be lifted to install insulation, but there are some measures that can help. Clearly, you can’t improve the insulation value of the boards, but you can improve the effect of any rugs and carpets. Their insulation value will be improved considerably if you put them on a foam underlay, and even more so if you can add an aluminised foam layer, obtainable from DIY outlets or heating and plumbers’ merchants. Aluminium kitchen foil will also be effective, though it may not last long. The aluminium reflects heat back into the room and reduces convection losses.
Heat loss through the gaps between boards can be reduced by filling them with flexible cork or wood-fibre strips, available from DIY outlets and flooring stores. The filler should be glued on one side only and pushed into the gap, finishing flush or slightly above the surface. Any protrusions can be easily sanded away. Gaps between the floor and skirtings can also be filled in this way. Indirect measures recognise that draughts can only enter the equation if the incoming air can escape elsewhere. This means sealing gaps around windows and doors with draught strippers, not forgetting the loft hatch and other openings into the loft.
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Many timber floors have excessive underfloor ventilation; this can be reduced by sealing up some of the perforated air bricks in the outside walls, especially those facing the prevailing wind direction, though this should be done only under expert advice. The same goes for room ventilation openings into cavity walls.
Michael Kilcommons is a chartered civil engineer based in Winchester