We will be renovating the basement into a suite but we’re concerned about the possibility of noise transferring through the floor from the tenants below. How can we deaden or prevent this noise transfer?

Unfortunately there is no way to completely stop noise from spilling into an adjacent suite. Usually the base notes of a stereo system are the most difficult to deal with. The success of any assembly at reducing sound transfer is often directly proportionate to your budget, (the more you spend, the more effective the results). Here are some typical sound reducing floor assemblies that you can use in singly or in combination if your budget can afford it.

The simplest and most common strategy is to fill the floor joist cavity with fiberglass batt insulation. Before installing the ceiling drywall in the suite you can also install resilient sound channels perpendicular to the floor / ceiling joists. The ceiling drywall is then attached or hung from these channels. This creates an air gap and reduces the contact surfaces between the drywall and the floor / ceiling joists, thus reducing sound transmission. If you increase the drywall thickness to 5/8 inch from ½ inch your assembly will benefit from the additional mass. Although less common, some assemblies substitute “donna conna” soundboard for the resilient channels and attach the drywall through the board to the floor / ceiling joists with longer screws.

Since one of the best sound deadeners is mass you can also consider laying heavy underlay and carpet on the upper side of the assembly. Although more costly and difficult to install, the best single component in sound control is a 1 ½ inch skim coat of concrete on the upper side of the floor / ceiling assembly.  If you have a friend, contractor or building inspector with a copy of the Building Code you can research the amount of sound transmission for various assemblies under the heading “sound transmission class” ratings. An “STR” of 50 is considered the standard minimum in residential construction today.  To give you a practical example of the effectiveness you can expect from these assemblies, visit a modern (15 years or newer) apartment building. The floor / ceiling assemblies between suites will probably be a combination of concrete skim coat, R20 insulation, resilient channel and 5/8 inch drywall.