Impact sound in timber construction
Sustainable construction requires maximum sound insulation with minimum use of resources. This requires floor structures with ecological building materials and good impact sound insulation. We use our impact sound test bench to develop new, efficient floor structures.
Good sound insulation can easily be achieved with heavy concrete ceilings and impact sound insulation. However, this construction method performs poorly in terms of sustainability and the construction process. Lightweight wooden ceilings are much better. For sound insulation, these are weighted with an additional mass according to the current state of the art. Wood-concrete composite ceilings (HBV), heavy underlay floors or fills are common. Unfortunately, these measures considerably worsen the climate balance of the timber construction and its deconstructability.
We test innovative floor structures with comparative measurements for our customers in our impact sound test bench. The impact sound test bench is the result of several bachelor theses at the Bern University of Applied Sciences in Biel.
Impact sound measurements on the test bench
We use the impact sound test bench to measure the change in impact sound insulation by adjusting individual layers. In this example, a tried and tested floor structure serves as a reference variant. One layer is changed in each of two variants and the influence on the sound insulation values and the ecological balance is analyzed.
The test method is based on the ISO 16251-1 standard. A standard hammer mill is used as the impact sound source. The structure-borne sound level is determined on the underside of the carrier plate by means of acceleration measurement, which is specified as the velocity level Lv. The ΔLv to the test ceiling is formed from the determined velocity level of the reference ceiling. This provides a statement on the change in impact sound insulation compared to the reference ceiling. The four corners of the support plate are softly supported and thus decoupled from the test stand. The test ceiling with dimensions of 100 cm × 100 cm lies above it. The vertical natural frequency of the test specimens on the elastic supports is individually adjusted to 8 Hz for each test specimen. The vibration acceleration is measured at ten positions using several uniaxial piezoelectric accelerometers. The signals are amplified, Fourier transformed and filtered into one-third octave bands and displayed as effective values. Vibration calibration is carried out in accordance with the requirements of ISO 16063 (all parts).
Elastically bound chippings fill from Köhnke for sound insulation
An elastically bonded chippings fill improves sound insulation and at the same time acts as a leveling fill. The inexpensive and quick-to-install chippings fill replaces HBV ceilings. It also results in a weight saving of approx. 50 % compared to concrete. Due to the many advantages, Timbatec uses this system in residential and commercial buildings and dispenses with HBV ceilings.
Notes
No water escapes from the bonded chippings fill. It can usually be applied directly to the wooden ceilings without a separating layer. On delicate substrates or with certain lignature systems, a separating fleece must be laid. This should be done before any cables (electrical or sanitary pipes). An edge strip is generally not necessary, but can be applied in the case of moisture-sensitive walls or for the subsequent underlay floors.
Material thickness: The fill is normally applied in a thickness of 50 mm to 80 mm. Thinner layer thicknesses (at least 30 mm) bring considerably less improvement in sound insulation; thicknesses over 80 mm have no significant benefit according to the manufacturer of the binder.
Drying: The water-based binder requires good drying conditions. The room temperature should be at least 15° C and good ventilation must be ensured. If the climate is poor (high humidity and/or cold temperatures), in the worst case no drying will take place at all. The other layers can be laid once the chippings layer has dried completely and is firm to walk on.
General: As this system is based on 4-8 mm chippings, slight differences in height are to be expected. A fine leveling layer (dry fill) must therefore be provided for dry floors. The Köhnke K 102-CH bonded chippings fill is a leveling layer and does not have a solid surface. Construction site operation is therefore only possible to a very limited extent; wooden boards may have to be laid for protection.