ᐅ Double insulation = better soundproofing?

Hello,

I am currently insulating the interior of my house (timber frame construction). For the interior walls and ceilings, I need to install 4cm (1.5 inches) of Rockwool stone wool insulation. Since I still have some space in the walls, I am considering installing two layers of 4cm (1.5 inches) each.

Do you think this would provide any benefits in terms of soundproofing?

Regards,
Micha

Soundproofing usually requires mass, while insulation often needs almost the opposite. Of course, doubling up on a small amount of mass is better than nothing, but I wouldn’t expect miracles. If you want soundproofing, build a 23cm (9 inches) wall using 1600 density calcium silicate blocks. (Warning: genuine sarcasm).

Soundproofing and thermal insulation contradict each other. Materials suitable for soundproofing are not ideal for thermal insulation—soundproofing is achieved using as heavy materials as possible, while thermal insulation requires lightweight materials with a high proportion of enclosed air. The additional 4cm (1.5 inches) of internal insulation is therefore intended solely for thermal insulation. However, you should consider that, due to building physics, for external walls a maximum of 20% of the insulation thickness should be placed on the room side, on this side of the inner frame closure—probably an OSB board.

Among the various insulation materials, mineral wool still offers the best soundproofing.