How Effective Are Cordwood Walls Against Sound Insulation?

Cordwood masonry construction involves stacking logs end-to-end, often with insulation materials like sawdust or perlite in between the logs. This technique can create a solid wall with a high thermal mass, which can also provide some level of sound insulation. However, the sound-blocking effectiveness of cordwood walls is generally limited to frequencies below 500 Hz, where the sound waves are longer and can be more easily absorbed by the cordwood and mortar.

Factors Affecting Sound Insulation in Cordwood Walls

To improve the sound insulation of cordwood walls, builders can use a combination of techniques. One approach is to use a high-density mortar mix, such as a mix with a high silica content, which can help to fill in gaps between the cordwood logs and reduce sound transmission. Another option is to add insulation materials like fiberglass or recycled denim to the wall cavity, which can help to absorb sound waves and reduce transmission. In general, cordwood walls with a high density of insulation materials (such as 2-3 inches of insulation per foot of wall) can achieve sound transmission class (STC) ratings of 25-35, which is comparable to other types of masonry construction.

Designing for Sound Insulation in Cordwood Buildings

When designing a cordwood building for sound insulation, builders should consider the frequency range of the sounds they want to block. For example, if the goal is to reduce traffic noise, which typically falls in the frequency range of 100-200 Hz, a cordwood wall with a high density of insulation materials and a high-density mortar mix may be sufficient. However, if the goal is to block higher-frequency sounds like conversation or music, additional sound-blocking materials like mass-loaded vinyl or acoustic caulk may be necessary.