ᐅ Impact sound and thermal insulation bonded beneath multi-layer engineered hardwood flooring

Hello everyone,

I searched the forum but didn’t really find a suitable thread, so I’m starting a new one.

In a ground-floor apartment of a 1970s building, I would like to install engineered hardwood flooring. The ceiling of the basement below is not insulated. From experience over the past winters, I can say that the floor gets quite cold. Therefore, I have been looking for an underlayment that provides both impact sound insulation and thermal insulation.

I came across cork as an option. However, since I want to glue both the underlayment and the hardwood itself, I need a glueable alternative to regular cork. Floating installation is ruled out for several reasons.

A company recommended the Kork-Pur underlay from Knauf (3mm (0.1 inch)) combined with Knauf adhesive for this purpose.

What are your thoughts? I couldn’t find much information online... I’m sure there are other recommended products that would serve this purpose.

Thank you in advance.

Good luck

oxxe235 schrieb:

I had a company recommend the cork foam boards from Knauf (3mm) combined with Knauf adhesive for this purpose.

What do you think about that?

From an insulation perspective? Nothing at all, as it is ineffective.
As impact sound insulation? If the parquet is glued down, it does nothing, because there is a basement underneath you. Nobody is bothered by impact noise there, and the effect inside the apartment is barely noticeable.

Are you the owner of the apartment, the house, or just a tenant? I’m getting at the fact that 5cm (2 inches) of insulation below the basement ceiling is much better than having no cork insulation at all.

Thank you for the quick reply!

Ineffective? Then why is cork promoted everywhere for its excellent thermal insulation properties, and why is it specifically mentioned that it should not be used with underfloor heating because of these properties?

In this house, everyone is bothered by impact sound, and the insulation needs to be as effective as possible. Here, the heating pipes are installed under the screed in such a way that they are touching it. In many places, there are acoustic bridges directly to the walls, etc. This means that my impact noise travels through the pipes to the floors above or to the neighbors.

I am the owner of the apartment, and no, I will not be pouring a new screed.

The basement ceiling will not be insulated in the near future.

oxxe235 schrieb:

Ineffective? Then why is cork so widely praised for its excellent thermal insulation properties and specifically noted as unsuitable for use with underfloor heating because of these characteristics?

The same is said about hardwood flooring – it just doesn’t conduct heat very well. That’s why it feels warm underfoot, even if the floor temperature is the same as tiles.
Yes, it insulates about as well as low-quality mineral wool or similar materials – but you only have 3mm (1/8 inch). To insulate a wall to current standards, you need around 18–20cm (7–8 inches) of cork. That’s why it’s said that 3mm is negligible and you won’t notice any difference.

oxxe235 schrieb:

In this house, everyone is bothered by the impact noise

Impact sound is the noise perceived BELOW you. Since there’s only a basement beneath you, impact sound insulation doesn’t matter.

Here is my brief response to the original question:

1. You either have impact sound insulation or thermal insulation. There is no construction layer that can satisfactorily provide both.

------------

2. Cork, as boards or rolls, used for thermal insulation is wishful thinking, nothing more. "Nordanney" has correctly provided all relevant information on this topic!

--------------

3. Are you considering interior insulation in principle? Fine, it will never achieve the desired effect, but fundamentally, anyone dealing with interior thermal insulation should thoroughly study the building physics basics beforehand. Keyword: "How can I cheaply and easily move the dew point below my parquet floor?"

---------

4. If installations are embedded in the screed, it cannot be considered compliant with building standards. This raises the general question of where such knowledge originates. Quote: "Here, heating pipes are laid under the screed such that they touch it." It is difficult to understand who or what is supposed to be touching and how this was determined.

To summarize:
a) Cork is not a suitable thermal insulation material, no matter who claims cork can serve this purpose.
b) 3mm cork as thermal insulation is unrealistic!
c) Thermal insulation is always installed on the cold side of a building component and only in specific cases together with a vapor barrier on the warm side. For uninsulated floors above ventilated (i.e., cold) basements, insulation of around 10cm (4 inches) on the basement ceiling is recommended. Anything else makes no sense, as heat transfer cannot be effectively reduced.

-----------------------

Information from the internet can—especially in construction—lead to significant damage due to misunderstood or misapplied knowledge!

Hoping my words find fertile ground: KlaRa