Which floor insulates sound best?

Answer

Dear Eva,

It depends on which insulation you mean. There is one hand airborne sound insulation which is aimed at limiting the transmission of airborne noise between two spaces. Airborne sounds are all sounds in which the air is made to vibrate directly (because sound is a vibration), such as through vocal cords (speech), loudspeakers in TVs, radios, mobile phones, … On the other hand, there is impact sound insulation who want to limit the transfer of contact noise between two rooms. Contact sounds are all sounds that end up in the building structure through (usually) brief contact between a subject (walking person) or object (sliding chair, …).

In front of airborne sound insulation can you make the split into vertical airborne sound insulation to limit vertical sound transmission (as in your question) or horizontal to limit the horizontal.

In front of vertical airborne sound insulation the mass of the floor is the determining parameter. A solid concrete floor, of which you speak, is optimal as this is the heaviest building material used in floors (in any case a lot heavier than wooden floors where the air sound insulation is not favourable). The floor must indeed be solid. Vaults weigh a lot less: a 16 cm thick vault only corresponds to about 10 cm of solid concrete floor (so better pre-cast + compression layer). A thickness of 20 cm solid concrete (with a screed on top of course) is usually sufficient to achieve the 54 dB sound pressure level difference that is required in the standard between, for example, two apartments for normal comfort. If the thickness is smaller, it depends on the construction of the walls, because sound is also transmitted via the connecting nodes between floors and walls (so-called flanking transmission). The following applies: heavy elements (sand-lime brick, for example) are better than light ones (fast-build masonry), although elastic strips can be used between floor and wall and/or between wall and ceiling to limit flanking sound transmission.

In front of horizontal airborne sound insulation do you have on the one hand”single stonewalls and the other double walls. Bee single stone walls again the masses play. Light, bending-resistant materials such as aerated concrete, gypsum blocks, light quick-build masonry and profiled metal sheets can also be avoided because of another phenomenon (coincidence, which would drive us too far).

Double walls enjoy a resonance principle, which means that the sound insulation can be excellent even with light structures (such as plasterboard). With double walls, the following principles apply to increase the sound insulation:

• Heavy cavity leaves and wide cavity
• Acoustic absorption in a cavity (such as mineral wool)
• For glass and light, bending-resistant materials: different cavity wall thicknesses
• As few rigid connections as possible between the two cavity leaves: preferably no or, if necessary, elastic anchors

In any case be chinks or gaps (for sockets, pipe penetrations, …) to avoid! If there are cracks or leaks, all the above principles are of less or no use: these should therefore be avoided first.

Regarding impact sound insulation are we only able to take concrete measures for contact noises introduced in the floor (of course also the most common). Then there are three options that may or may not be combined:

• Floating screed: screed resting on an elastic layer and also along the edges and at pipe penetrations not making any contact with the building structure
• Suspended ceiling in the room below: this creates a (horizontal) “double wall” principle, which was also good for airborne sound insulation
• Flexible material such as carpet as the top layer

So, hopefully the above is a satisfactory answer to your question.

With quiet regards,

Pieter Schevenels