3.7 Details Required When Using Chimneys

When using ventilation chimneys, considerable care is required with respect to detailing. Illustration 1 shows how if not properly detailed, the use of ventilation chimneys can seriously compromise the sound insulation between multiple spaces.

When using chimneys it is also important to consider build-ability. Simple stud walls cannot be used, since it is not possible to build the inner skin of the shaft. The walls to the shaft must contain two leafs such to maintain the sound insulation across the shaft. The solution is to use a Shaft Wall system with an acoustic rating of 50 dB Rw+ or to form the shaft using dense 140mm block work. Note that a 50 dB Rw wall may not be appropriate in all instances.

The positioning of the ventilation shaft is also important; care must be taken not to breach the acoustic performance of separating walls and floors. Illustration 2 provides the recommended detail; here the separating wall and corridor wall are built first. It can also be seen that each shaft is formed over two separate penetrations within the floor slab. Once the corridor wall and separating walls are built the walls forming the shaft can be built. This detail should ensure the horizontal and vertical sound insulation between cellular spaces.