Noise: Environmental: Insulating the Home

Noise - Environmental - Insulating the Home - Floors & Ceilings

Improving Floors/Ceilings

Click here and then search for "noise" to find the proposed revisions to the Building Regulations which cover conversions and suitable sound insulation treatments to floors.

Firstly, it is worth inspecting the construction for weaknesses, such as gaps between boards in timber floors, poorly isolated flues/chimneys or ventilation ducts, pipework and so on. Sound can also be transmitted via the walls which flank the separating floor, particularly if they are medium-weight; this "flanking transmission" may limit the maximum sound insulation attainable; again suitable tests can indicate whether flanking transmission (sound coming up side walls or chimneys) is important. Under some circumstances flanking transmission can be the most important sound path; so treating the floor may make little if any improvement to the overall sound insulation.

Sound transmitted through floors falls into two categories; airborne (speech, music etc.) and impact (footsteps). Impact sound can be greatly reduced by a soft floor covering such as carpet on thick underlay, but this would not affect airborne sound. An effective way to improve both types of sound insulation is to construct a new ceiling supported on independent joists below the existing ceiling.

Patch up any holes, gaps or cracks in the existing ceiling, for example if light fittings have been removed.
The new ceiling should be of a minimum of 25mm plasterboard (preferably in two layers arranged to have staggered and sealed joints) with a cavity of at least 150mm between the ceilings;
A layer of mineral wool or glass fibre insulation at least 50mm thick and of about 50kg/m3 density should be laid in the cavity; note that this "insulation" is thermal insulation; actually the layer is "absorbing" sound as it passes through the cavity.
Surface mount any new fittings (e.g. lights) on the new ceiling; cutting holes in the new ceiling for say downlighters, will effectively damage the sound insulation performance you have just worked so hard to achieve.

Naturally such treatment is only possible where the rooms are high enough to permit a loss of 150 mm or more. Alternatively, the sound insulation may be improved to some extent by filling the space between the floor joists with a heavy, loose fill "pugging" material. Examples would be dry sand or high density pelleted mineral wool. You must ensure that the structure can support the extra weight!!

A further alternative would be a 'floating' floor, for example the top "floating" layer would consist of 18mm Tongue and Groove chipboard, bonded to a layer of 19mm plasterboard; The top layer would be laid on a spongy layer which should be 25mm mineral fibre having a density of around 100kg/m3 or similar; this spongy layer would extend up around the floating layer to provide isolation from the walls, the gap between the floating layer and the walls being around 10mm. The spongy layer itself would lie upon or could be glued to the existing floor after any gaps or cracks in the floor had been made good. It is important that there are no fixings through the top layer into the existing floor, as this would damage the structural isolation. The increase in floor height would be around 60 mm, which can cause considerable problems with doors, skirting boards, power sockets and so on.

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