Sometimes, insulation is installed next to a party wall to stop noise from getting through it. But before insulation goes in, you should know where the noise comes from and how it travels to your side of the wall. The two most common ways for noise to get through a wall, roof, or floor structure are via the air and via the wall, roof, or floor itself.
When this approach is chosen, insulation material is simply pushed against the party wall before its hidden by a finished partition or other layers. Density should be your main factor when choosing insulation material.
The Party Wall Act could say that installing insulation in party walls is 'notifiable,' as per decisions in previous court cases that show the importance of plastering to these walls. For this reason, since the wall is impacted by these works, a Notice is required. The Notice must be sent to the Adjoining Owner(s) so they can respond to it.