This is the area that prevents any dampness and moisture enter the house. As the foundations are built and the walls are going up, there has to be a certain level where you will have to place damp protection courses to stop any moisture from rising into the walls and ending up in the house. This is done by positioning a layer of DPC in the wall, usually between 150 - 225 mm above the ground on the outside of the cavity wall. It is very important to make sure that the DPC is positioned correctly in the cavity wall to stop any damp rising in the walls. DPC comes in variety of sizes and it is also used for protection against damp around lintels, cills, windows, doors and anywhere else that is needed.
A radon barrier covers the whole area of the floor of the house and around the foundation. The reason for this barrier is to stop the penetration of radon gas into the building. Radon is a radioactive gas which can cause lung cancer and under the Building Regulations on all new homes every percussion should be taken to stop this gas entering the house. Even though the radon barrier can be fitted by the self builders themselves, it is recommended that you should make sure that a professional fitter of radon barrier does this job for you and give you a certificate that the job is done. Do remember, the gas can enter the building through the smallest gap in the radon barrier. For an average house, the cost of fitting the barrier is between 800 - 1500 Euros. However you should get estimates from a few different contractors for this job on your project.