building acoustics
Klas Hagberg
Acouwood partnership with Kuster and Partner
Acouwood partnership with Kuster and Partner

sound insulation

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Flanking transmission in CLT dwellings – How to design a proper ceiling

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Flanking transmission in CLT dwellings – How to design a proper ceiling

A common way to construct Cross Laminated Timber (CLT) dwellings is to mount the floor slabs continuous over several apartments, thereby reducing the number of CLT elements and work time with the crane on site. There are some crucial acoustic factors to consider if you are thinking about this route. CLT is sensitive to flanking transmission in the middle frequency range from about 125-160 Hz and upwards. If CLT elements are mounted between apartments and are exposed within the dwelling, the resulting sound insulation will not fulfill Swedish requirements. The resulting sound insulation R´w will likely be in the 40-50 dB range and not 52 dB as it should be. A common way to solve this issue is to install a resilient ceiling, and the solution can be optimized in different ways depending on the rest of the structure.

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Vertical flanking sound transmission in CLT dwellings

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Vertical flanking sound transmission in CLT dwellings

Dwellings with Cross Laminated Timber (CLT) have become very popular lately. When designing a multi-family dwelling in CLT there are some critical factors to consider with regards to acoustics and sound insulation. A characteristic property of CLT is that it is very sensitive to flanking transmission i.e. sound transmission between two rooms another path than through the directly separating partition. What this means in practice, is that whatever you do, do NOT mount CLT elements that are continuous between two dwellings. That is a recipe for disaster. It might work in premises or between rooms with lower requirements, but in dwellings it is a big NO-NO. So, what solutions are there?

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How to use the impact ball to evalute impact sound insulation in timber buildings

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How to use the impact ball to evalute impact sound insulation in timber buildings

The most common method to evaluate impact sound insulation in buildings, is the tapping machine. One of the issues with the tapping machine however, is that it does not resemble actual walking sound at all. If you have ever visited a field measurement of impact sound insulation, you will probably recognize the hammering noise that the acoustician creates. Another method that is less common, is the so called impact ball. The impact ball might very well be the most expensive ball in the world, with its four-digit price tag (five if you’re swedish)!