Are two impact sound insulation underlays worthwhile?

Hello everyone,

we have been considering for a long time whether to equip the apartments in our multi-family house with vinyl or tiles. We live on the ground floor. The upper floor and attic are rented out. A new thin-bed screed with underfloor heating has been installed. There is mineral wool under the screed.

Our neighbor has had bad experiences with tiles on the upper floors regarding impact sound, so we are somewhat skeptical about tiles. Therefore, we will lay vinyl in the attic for now. The click vinyl we have in mind already has impact sound insulation integrated (black rubber coating on the underside). Does it actually make sense to install a second impact sound underlay beneath the click vinyl? One variant is allowed for this vinyl, according to the seller, with a thickness of 1.8mm. (approx. €3.90 per m²)

1. Are these things any good, or would two layers be counterproductive?

2. Tiles are planned for the bathrooms. Here I have read about decoupling mats that also have impact sound properties (apparently up to 17 or 18dB). Does anyone have experience with this, or would it be money thrown away? (approx. €9-11/m²)

Best regards

Hello "Netzplan". I personally consider it positive when someone informs themselves in advance about the advantages and possibly also disadvantages of their intended execution of a floor covering construction. Clear answers to your questions: A 2-layer structure of the so-called "Trittschallfolie" is definitely counterproductive. Why? Well, the fittings of the locks are nowadays very finely designed. They hold (there are actually no standards for the required tensile strength here), and thus they fulfill their purpose. If you place another ductile layer under the floor elements, very likely bending moments will arise between the elements, affecting the edges, which inevitably has an unfavorable effect on the locking mechanism. That means in the "case of emergency": gaps will appear everywhere between the element edges because the locks open on the sides. ---------- Regarding your second question: The purpose of decoupling mats is to be able to transfer a critical screed surface into a reasonably stable state so that the layers applied by a floor/tile installer or their stresses cannot affect the screed surface. This has nothing to do with sound insulation! Sound insulation that deserves this name is always located beneath a screed (this inevitably also results from the test specification for impact sound measurements, whose test setup always considers a concrete ceiling as support). ----------------------------- Good luck with your further planning: KlaRa

I had a soundproofing fill applied on a solid wood ceiling on the upper floor and am very satisfied with the effect -> Köhnke gravel fill 5-8mm with binder K102 approx. 80mm thick.

70m² cost about €2200 in April 2021. The binder K102 (similar to sticky rubber) turns the loose gravel into a tough elastic board.

A 2-layer construction of the so-called "impact sound foil" is definitely counterproductive.

Thank you for the very detailed assistance. Counterproductive would then rather be towards the "joints" between the vinyl, but not regarding impact sound? Here, a further improvement in double impact sound reduction might possibly be expected? For example, there is the "b!design insulating underlay Silent Underlay Profi," which is apparently specially developed for vinyl/SPC/rigid floors. However, I am currently reading "Not suitable for vinyl floors with integrated impact sound insulation."

It has nothing to do with sound insulation!

I have, for example, found the following products: PCI POLYSILENT PLUS - 16dB - (55€/m²) Schlüter-DITRA-SOUND - 13dB - (21€/m²) Sopro TEB 664 - 17dB - (19€/m²) Dural DURABASE SW14 - 14dB - (13€/m²) Impact sound is explicitly mentioned here. Somehow, I cannot quite imagine how this should work if the decoupling mat is glued with mortar or adhesive.

I had a sound insulation screed applied on a solid wood ceiling on the upper floor and am very satisfied with the effect

Good. Under the screed, we also have mineral wool and bonded filling. Unfortunately, the mineral wool is only 2-3 cm. The filling underneath (Thermobound EPS granulate) varies depending on the floor between 0-7 cm. On the packaging, under "special advantages" it said = sound insulating, but no details here.

Wouldn't that be counterproductive more in the direction of "joints" between the vinyl, but not regarding impact sound?

Please read exactly what I wrote! We are talking here about a possible total failure if the locks fail due to the ductility of the subfloor (double foil layer). All these foils that promise a reduction in impact sound cannot deliver what insulation beneath at least a 45mm thick mineral screed as a floating construction can achieve. All these foils are rather a "crackling protection" for thin-layer floor elements (such as laminate floor elements), if there were still grains of sand on the screed surface. SOUND INSULATION is much more complex than the layman suspects. It consists of structure-borne, airborne, and room sound. The only thing such "impact sound foils" can be conditionally used against is the "clicking noise" that occurs when walking on loosely laid laminate floor elements. However, this has nothing to do with "sound insulation in residential construction." So the consumer remains responsible for deciding what he believes and ultimately buys/installs; the experts can only give their advice on this. -------------------------------- Regards: KlaRa

These foil products, which promise a reduction of impact sound, cannot deliver what insulation beneath a minimum 45mm thick mineral screed as a floating construction can achieve.

Hello Klara, yes, that’s true. I would therefore forgo a second layer. It’s "only" about impact sound, so an independent question: Regarding impact sound, it would certainly make a big difference whether you use vinyl with integrated impact sound insulation or tile the screed directly.