Sound Theory

Sound level

The sound level is indicated in dB(A). The value is corrected for the ear’s varying sensitivity to different frequencies.

Airborne sound insulation: A construction’s (for example, floor structures) ability to isolate against typical airborne sound such as speech and speaker sound, etc. In practice, it is the difference in sound pressure levels on each side of a dividing structure. It is expressed in dB.

The higher the value, the better the isolation.

Rw = a construction’s airborne sound insulation measured in the laboratory.

R’w = field-measured value. This is the value one can expect in a finished building. This is usually 3-5 dB lower than the laboratory-measured value, due to sound transmission via adjacent structures, as well as workmanship. The requirement is for the field-measured value.

Impact sound: occurs when, among other things, foot traffic on the floor sets the floor structure and the walls under it in motion. This results in sound radiation to the room below.

Impact sound level: measured by placing a standardized tapping machine on the floor structure, and the sound pressure level is measured in the room below.

L’n,w = weighted, field-measured normalized impact sound level. The lower the value, the better the construction.

Flanking transmission = sound transmitted between two rooms via adjacent (flanking) construction elements. It is also used for all sound transmission that does not pass directly through the separating structure, such as through ducts and gaps or along the edge, above the ceiling, etc.

NS 8175 Sound levels in buildings

• Class A
  Corresponds to particularly good sound levels at which affected persons are only disturbed by sound and noise in exceptional cases.
  
  
• Class B
  Corresponds to sound levels clearly better than the minimum requirements given in class C and is considered a good sound standard. Affected persons may be disturbed by sound and noise to a certain extent.
  
  
• Class C
  Corresponds to the intentions for minimum requirements in the building regulations, i.e. R’w ≥ 55 dB (airborne sound) and L’n,w ≤ 53dB (impact sound)

In residential buildings there is an additional requirement in the form of a correction factor for the range 50-100 Hz in classes A and B.

In order to avoid approval of some designs that are not “good enough” even though they meet the criteria of the current building regulations, i.e. class C, NS 8175 recommends that a correction factor is also added in class C (for 50-100Hz) so that:

L’n,w + korrection factor ≤ 53 dB.

When this correction addition is included in the metric, compliance between regulations and the expectations of residents is improved.

This is to ensure better sound insulation in the bass range

But especially for impact sound, even lower frequencies (below 50 Hz) from walking comprise the subjective for people.

Complaints about impact sound are quite common when only marginally fulfilling the requirement in class C.

The requirements given in higher classes may better match the expectations of residents.

Measurements given satisfy the minimum requirement in Class C. c-corrections are not taken as a basis for measurements of impact noise and airborne noise.

Sound in joists

Airborn noise

Airborne noise insulation for acoustic joists, R’w, measured in dB. Airborne noise insulation is the field-measured reduction of airborne noise that can be expected through the floor divider in a finished building. The higher the value, the better the airborne noise insulation. This is the field measured value required by the regulations.The regulations recommend that airborne sound insulation should not be lower than 55 dB for floor dividers in wooden houses over several floors.

Impact sound

Impact sound insulation for acoustic joists, L’n,w, measured in dB. The impact sound insulation is the field-measured value of, for example, pedestrian traffic on the floor divider that can be expected to pass through the construction in the finished building. The lower the value, the better the impact sound reduction. This is the field measured value required by the regulations. Impact sound insulation is recommended in the regulations to be equal to or less than 53 dB for floor dividers in wooden houses over several floors.

Tabell som viser grenseverdi for lydklasse C ihht NS 8175.

Fig. 1 Lydbjelkelag

General text/picture about sound beam layers that show and describe requirements for sealing, edge support, minimum quality for standard plasterboard and fire plasterboard etc.

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To achieve the best sound insulation construction, the following should be done:

• Joists are recommended to be dimensioned according to the joist table for the comfort criterion and any reduction factors for the ceiling and subfloor type should be taken into account.
• Stiffer joists are better acoustically than less stiff joists.
• Follow the manufacturer’s installation instructions when installing ceilings using acoustic hangers and battens or acoustic profiles. It is important that these are loaded with the right load/area to function optimally.
• The ceiling must be constructed of acoustic radiation-reducing panels in a minimum of two layers.
• Floating floors on sound-absorbing surfaces ensure minimal flanking noise transmission.
• A ventilated subfloor (Forestia slotted floor) is necessary to achieve the maximum effect of the damping layer (impact sound panels).
• In addition to the sound properties of the actual joists, it must also be taken into account that other sound transmission paths can be limiting factors. Particular attention should be paid to the connection between the joists and other supporting structures. High accuracy is required for sealing. This and other important elements are described in SINTEF Byggforsk byggdetalj 522,511.

Detailed solutions

Fire safety requirements and solutions

Materials are classified as

• Non-flammable
• Combustible
• Limited flammable

NS-EN 13501-1

classifies interior cladding according to the fire-technical properties in classes A – F, where A stands for non-combustible material and F stands for no requirements. D stands for combustible material.

Floors are classified according to their ability to limit the spread of fire in coverings and substrates, as well as their ability to contribute to the development of smoke. Floor coverings are classified in fire-technical class G (NS3919), Dfl-s1/D-s2,d0 (NS-EN 13501-1).

In a complete fire-documented floor divider, the ceiling is also included as an important element. A ceiling of two layers of chipboard can be used up to fire resistance R60.

NS-EN 13501-1 specifies the surface classes D-s2,d0 and B-s1,d0. These classes specify requirements for the flammability of the surface, and the extent to which the surface contributes to the production of smoke and heat in a fire.

The table below indicates whether or not other conditions/requirements allow the use of chipboard (D-s2, d0) in ceilings and on walls: