The design objective is to construct an airtight, and therefore substantially radon-proof, barrier across the whole of the building including the floor and walls. This objective may be achieved by incorporating measures within conventional types of floor construction.
In-situ (ground bearing) concrete floor
In the example illustrated in Figure 3.1 the damp proof membrane, which in this case is located beneath the in-situ concrete provides a radon proof barrier. The joints between the membrane must be sealed to make them as gas-tight as possible. Service pipes must be sealed and the cavity tray must be joined to the floor membrane and sealed.
Figure 3.1 Radon protection – in-situ (ground bearing) concrete floor Source (BRE, 1997)
To provide full protection with this type of floor construction the floor needs to be reinforced and supported on the inner leaf of the cavity wall, since a traditional ground bearing slab could settle on completion and rupture the radon barrier at the point where the slab meets the external wall as shown in Figure 3.2. In addition to these requirements supplementary protection must be provided by installing a subfloor depressurisation system. The damp proof membrane can be laid either below or above the concrete subfloor.
Figure 3.2 Radon protection – in-situ (ground bearing) concrete floor built into cavity wall Source (BRE, 1997)
Suspended concrete (beam and block) floor
As illustrated in Figure 3.3 basic radon protection is provided by a vapour proof membrane which is placed above a suspended concrete floor and linked to a cavity tray in the external walls. The joints between the sheets which form the membrane and the cavity tray must be sealed to make the construction air-tight as possible. Seals must be provided around service penetrations.
Figure 3.3 Radon protection – suspended (beam and block) floor Source (BRE, 1997)
To provide full radon protection supplementary protection must be provided by locating underfloor vents on two or more sides of the underfloor space.
Full radon protection is the only means of protecting timber floor construction. As illustrated in Figure 3.4 the radon proof barrier is provided within the concrete subfloor construction and continued across the cavity walls. Ventilation between the subfloor and timber floor is provided as with traditional construction.
Figure 3.4 Radon protection – timber floor Source (Personal Communication, 1997)
The supplementary protection is provided by providing ventilation above the radon barrier, this is the opposite of the other floor construction methods and requires further research.