In many different situations the additional sound insulation of the floor may be required, for example:
- The noisy neighbors downstairs (you can hear the quarrels, baby crying or TV).
- The premises of cafes, restaurants, shops or karaokes are located under the apartment.
- Technical premises with noisy pipes and transformers.
- Your downstairs neighbors complain about the noise of the footsteps they can hear from your apartment :-)
- Floor structures in the wooden houses.
The soundproofing of the floor is noticeably different from the solutions for walls and ceilings. Indeed, each floor design must not only increase the sound insulation but also provide the stable and durable structure. The floor must always be a floor, i.e. it must withstand the weight of people and furniture and be structurally sustainable. You must admit that no sound insulation makes sense if the floor springs under your feet and seems unsteady! Several standard solutions are used for soundproofing the floor. The two most common of them are the "floating" screed and the joisted floor. The soundproofing of wooden floors stands out; we will discuss this case in the end.
Before starting to discuss the structures, the distinction between the airborne and impact noise should be understood.
Theairborne noise is the noise transmitted through the air. When sound waves interact with the floor slab they rock it and make it oscillating and emitting the noise into your apartment. The examples of airborne noise are as follows: people talk, TV or music.
The impact noise is the noise arising from the impacts. When the floor slab is directly impacted, the vibrations arise and penetrate into the apartment from downstairs. The typical examples of the impact noise are as follows: footsteps, moving furniture, falling objects.
Although the standard concrete floor slabs comply with the norms for the airborne noise with difficulty (however, even the compliance with the norms does not guarantee the silence), none of such slabs are even close to meet the requirements for the impact noise! If the screed is applied directly onto the concrete in your apartment, then the downstairs apartment will exceed the norms of the Building Codes and Regulations (SNiP) for the impact noise for more than 20 dB! The downstairs neighbors will hear the sounds of ordinary footsteps and even the fall of a felt-tip pen!
That's why the floor should be always soundproofed, regardless of the type of you house or the flooring you plan to use!
HOW THE FLOOR SOUND INSULATION MAY BE INCREASED
Floating screed is the most popular option of soundproofing the floor. Floating screed means that the screed is not directly connected with either the floor slab or the walls: it is poured over the soundproofing materials!
By the way, the word "floating" can be written in quotes because this screed is actually very stable and does not differ from the usual screed. But from the point of view of sound waves, the screed is really strictly isolated from the building by means of a layer of special damping materials which prevents the vibrations to spread from the floor structure to the screed and vice versa. Some materials protect only from the impact noise; the others protect both from the impact and the airborne noises. The total thickness of the "floating" floor can vary from 5 to 10 cm depending on the selected sound insulation.
If you just need to meet the norms of the Building Codes and Regulations (SNiP) for the impact noise and to prevent the potential problems with your downstairs neighbors, then you should place the basic sound insulation MaxForte-ShumoIzol under the screed. This affordable backerboard intended for mounting under the screed helps not only to reduce significantly the impact noise coming from the neighbors apartment but also provides the high-quality waterproofing! However, no thin backerboard is able to “remove” the conversations from the downstairs!
If you want to protect yourself from the airborne noise from your neighbors' apartment, you will have to place the more efficient materials with a sound-absorbing layer under the screed, namely: MaxForte-SoundPRO or 110 kg/m3 MaxForte-ECOslab. The "floating" floor which increases the sound insulation from the airborne noise will automatically increase it by the impact noise as well.
Combining the different materials under the backerboard does not make sense since the soundproofing properties of the composite layer will be determined by the characteristics of the most efficient material, and the contribution of the other less effective layers will be equal to zero. Summing up the characteristics of different materials does not work!
Another good way to soundproof the floor is to make the joisted floor. Wooden joists should be installed on the special VibroStop Floor vibration insulating fasteners, and the 60 kg/m3 MaxForte-ECOslab sound-absorbing slabs should be placed between the joists. At the end, the entire structure should be coated with the sheets of plywood or OSB.
The joisted floor will help to increase the soundproofing against both the airborne and the impact noise: the vibration dampers under the joists will reduce the transmission of vibrations whilst the acoustic slabs between the joists will increase the sound insulation against the airborne noise!
Penetration of the impact noise can be reduced without using a sand-concrete screed since the easier ways exist! As a "floating" screed, you can use the dry flooring made from the plywood or the gypsum plasterboard sheets; the ready-made prefabricated KNAUF Superfloor can also be used. Applying a dry screed over the MaxForte-ShumoIzol layer allows to reduce significantly the transmission of the impact noise from your apartment to the downstairs apartment!
The prefabricated flooring will not take up much space (the floor will rise by 2-3 cm) and can be mounted in the already repaired apartment.
By way of conclusion it should be noted that only thin backerboards (MaxForte-ShumoIzol or its analogs) must be laid under the prefabricated floor. Such flooring should not be mounted over the sound-absorbing slabs (the MaxForte-ECOslab, Shumostop or Rockwool Floor Batts). Despite a noticeable increase in soundproofing against the impact noise, the similar structures based on the mineral wool plates will always reduce the soundproofing against the airborne noise! The fact is that the prefabricated screed made of gypsum plasterboard sheets (as well as of OSB or plywood) has a low mass. Because of this, the sound-absorbing slabs find themselves underloaded, and the whole structure may resonate so reducing the sound insulation! Moreover, such structure may lack the needed structural stability when low density mineral wool plates are used.
It is also obvious that placement of expanded clay, foam plastic or other building materials under the flooring is absolutely of no sense from the point of view of increasing the noise insulation!
CHOOSING THE OPTIMAL STRUCTURE
As we explained above, some soundproofing structures reduce only the impact noise while the others reduce both the impact and the airborne noises. When choosing the optimal floor soundproofing structure, it should be necessary that the following factors be taken into consideration:
- Who is disturbed by the noise? It seems obvious that since you are reading this article then you are disturbed by the noise. But sometimes the downstairs neighbors may be so disturbed by the impact noise from your apartment (for example, by the children's running or the ball games) that they negotiate on soundproofing the floor of your apartment.
- The nature and volume of the noise. Is it impact or airborne noise? How loud is the noise? Are there low-frequency components in the noise range?
- The carrying capacity of the floor structure. In the older houses, the floor structure may be too poor to withstand the screed. In such cases, the solution may be the joisted floor.
- Thickness and cost of the structure. This point is not directly relating the sound insulation, but the final choice of the structure is often determined by the restrictions in thickness or cost.
SOUNDPROOFING THE WOODEN FLOORS
Soundproofing the old houses with wooden floors should be discussed specially. After you bought an apartment, you may have a desire to disassemble the old flooring, throw out the slag backfilling and fill the space between the beams with new expanded clay or mineral wool. However, this can never be done!
The fact is that the sound insulation of the floor structure directly depends on its mass and tightness, but each wooden floor is sorely lacking both the first and the second! The material debris between the beams significantly increases the sound insulation because it makes the floor structure heavier and ensures its tightness. Replacing the slag with the expanded clay (or with the ordinary low-density mineral wool) creates the situation when the sound insulation (especially against the low frequencies) will only be determined by a thin layer of lath and plaster from the side of the downstairs apartment.
In an apartment with wooden floors, the sequence of actions to increase the noise insulation may be as follows:
- Dismantling the old flooring.
- Inspection of slag backfilling. It should lie evenly. Large pieces of concrete or bricks should be crushed into the small fragments.
- Fill the remaining empty space between the beams with one or two layers of the 60 kg/m3 MaxForte-ECOslabs.
- Place the MaxForte SoundPRO over the beams and cover the floor with two layers of plywood. The plywood sheets should be laid in a staggered manner so that the seams between the sheets could not match. It is important that the plywood is not screwed to the beams.
By following these recommendations, you can significantly increase sound insulation against the airborne and the impact noise!
Sound insulation of the floor can also be improved in another way - by assembling the joisted floor system as described above. When doing this, there is no need to disassemble the existing floor, but the height of the room will decrease.
ABOUT THIN CONSTRUCTIONS AND FINISHED REPAIR
Soundproofing the floor cannot be achieved by use of thin structures! If the noise from the downstairs neighbors interferes in you life, then replacing the backerboard under the laminate will not change your situation at all – you will just spend the money. Soundproofing layers under the laminate floor do not exist! This problem cannot be solved by placing any cork pads, foam plastic or even special “soundproof” membranes under the flooring: this is a very popular myth. However, people often cling to such an idea because it is simple and subtle.
The truth is that only the special 5-10 cm thick constructions can seriously improve the floor noise insulation. This is the main problem of soundproofing the floor after the repair is finished – it is impossible to get rid of the noise from the downstairs neighbors without significant investments and reworking the repair!
Therefore, it is important to soundproof the floor yet at the stage of apartment repair, earlier than the screed is applied and the joisted flooring is assembled. Never save on sound insulation against the downstairs neighbors: the spent money will allow you to live tranquilly with any neighbors (who cannot be chosen, by the way). Increasing the floor noise insulation after the repair is finished is much more difficult and requires much more investments!