Sound insulation of wooden houses. How noise transmission between levels is stopped

One argument used by those less confident in timber-framed houses is the propagation of noise between levels and through walls. Some even recount having lived for a time in old wooden cottages or houses and hearing everything going on in the other rooms. At first glance, this seems logical when you consider that wood has been the material of choice for musical instrument sound boxes for centuries. Wood produces sound by direct impact and amplifies or absorbs sound waves. We still forget that in all areas, including construction, technologies have evolved. There are ways of building and materials to stop the propagation of sound, but also regulations requiring their use in the construction of timber frame houses.

Comfort closely linked to noise level in the home

Comfort in a home also depends on the noise level inside. It directly affects the quality of life of the inhabitants. All the sounds around us - voices, knocks, bangs, creaks, creaking pipes, creaking pipes, shuffling chairs, music, horns, traffic - all add up to noise. Sound is a vibration that is transmitted through the air (voices, the noise of household appliances, traffic) or another medium through which it travels (banging against a wall or floor, falling or dragging objects). It has several units of measurement, but the one that refers to intensity is the decibel (dB). Vibration generates an amount of energy that reaches our ears and when it is above a certain level, it disturbs us.

The lowest sound level is 0 dB. This is the lowest vibration perceived by the human ear. The normal human voice level is 60 dB, and the average noise level in the home is 50 dB. Any noise that occurs in the home below this level (whispering, low-noise appliances) keeps the sound at the same level and the ear will not perceive it. If another sound occurs, also at 50 dB (doubling the noise source), the total level will add 3 dB and the ear will perceive the difference (53 dB) and it can become a discomfort factor. If another 10 dB is added to the total level, the ear will feel a doubling of the noise, which will be really unpleasant.

How sound travels

Sound travels like a wave and has a certain frequency, measured in hertz (Hz). There are low-frequency sounds (low-pitched musical instruments), medium-frequency sounds (vocals, the crackling of pipes, hammer blows) and high-frequency sounds (sounds emitted by electric guitars, for example). It is the mid-frequency sounds that are important from a construction point of view.

Sound travels from room to room not only through open spaces, but also through partitions or side walls, ceilings, ceilings, floorboards, wall cavities, ventilation or pipe openings. When sound hits the wall, the wall picks up the energy and transmits it further into the other room. This is direct propagation. But sound can also hit the ceiling or floor, which in turn picks up the energy and carries it to other rooms. This is indirect propagation and is weaker in intensity than direct. Sounds can also propagate by dispersion, i.e. moving through poorly made joints, cracks or uninsulated ancillary spaces.

Why noise travels more easily in wooden houses.

Firstly, because wood is a lighter material. The more mass a material has, the harder sound travels through it. Wood is a lightweight building material which gives it many advantages (simpler and cheaper foundation, earthquake resistance, etc), but sound insulation is not one of them. Therefore, one way of soundproofing is to increase the mass, but without affecting the strength structure. This is where insulating materials come into play, which, when introduced into the walls, increase the mass while at the same time changing the sound frequency.

Another reason why noise propagates easily are the so-called noise bridges. Basically, they are the reason sound propagates between levels. Like thermal bridges, these bridges must be broken. Sound bridges are formed at the contact between side walls and ceilings, between the ceiling of the lower level and the floor of the upper level, etc. The interruption, the sound break between the construction elements is made on the principle of decoupling. Materials that absorb and change the sound frequency are placed between the elements. The materials must be chosen according to the weight that weighs on them (number of levels, load on the house) because there is a danger of subsidence with repercussions on acoustic performance. The materials used are in the form of strips or mats (membranes) made of EPDM (synthetic rubber), polyurethane or cork.

Noise protection standard NP 005-2022

Design and Inspection of Timber Construction Standard NP 005-2022 provides that timber construction elements shall be constructed in accordance with the noise protection requirements laid down in Standard C125 - Acoustics in buildings and urban areas and SR EN 16798 - Energy performance of buildings. Ventilation of buildings. Environmental parameters for the design and assessment of the energy performance of buildings, relating to indoor air quality, thermal comfort, lighting and acoustics.

The standard emphasizes that providing adequate protection against noise is an important factor in ensuring indoor comfort in buildings. Sound insulation must therefore be a top priority at all stages of the interdisciplinary design process. Both airborne noise (voices, walking, music, outside noise) and the noise normally made by the building (sewage, hot water in pipes, etc.) must be taken into account.

To achieve good sound insulation, the standard recommends the following solutions:

• the insertion of vibro-absorbent insulation layers between wooden construction elements and interior or exterior finishes;
• the use of elastic elements to isolate the impact noise transmitted through the walls or floors at the joint between the construction elements;
• the use of sound-attenuating materials when installation components or systems pass through timber construction elements.

How wooden houses are now built

Acoustic performance in wooden buildings is improved by solutions that add a extra massby noise barriers and fitting of materials that uncouples construction elements.

Sound transmission through interior walls. Table-resort-table is a system that adds mass and changes the frequency of sound. A layer of sound insulating material is placed in the wall between two layers of wooden resistance elements. The principle is as follows: the sound wave first penetrates the first layer of wood, hits the insulation which weakens it before entering the second layer of wood. The different structure of the insulation will absorb some of the energy and change the frequency. So the sound heard on the other side of the wall will be very muffled.

Noise transmission between levels. One of the reasons for the sound transmission in old wooden houses was the shared floor and ceiling. Now multi-storey buildings are made with different modules attached to each other. The ground floor ceiling and the floor of the first floor are two separate structures. Both of them are built on the table-spring-table system, benefiting from sound deadening. Sound-attenuating membranes are used inside the floors. The floor is also acoustically decoupled from the wooden structure, so no sound is transmitted through the structure.

External sound transmission through walls. They follow the same principle of adding mass by using materials that shift frequencies and take energy from the sound. They are used on both the exterior walls and the roof. Special membranes are also used on the roof to attenuate rain noise on houses covered with tin. House by the lake has such a system, the attic is very well soundproofed, even during heavy rain, despite the sheeting on the roof.

Today's timber frame houses cannot be compared to those built more than 20 years ago. The field is very dynamic and is constantly developing and modernizing, which makes the performance of houses built now far superior to old wooden houses as well as to those made of traditional building materials. The frame houses built now are squeak-free, quiet and warm.