This sheer, which should be at least 8mls thick, not only blocks the naturally occurring radioactive gas from entering the house, but also keep moisture from wicking into the finished slab, where it can cause cracking. An inexpensive plastic pipe set in the slab prior to the pour can save you hundreds of dollars down the road if you detect elevated radon levels in your finished home.
   To minimize the impact of termites, some brands of rigid insulation come pre-treated with an environmentally safe deterrent. The best defense, however, may be a good drainage system, since termites need moisture to thrive. By coating the exterior of the foundation wall with a water-proofer, installing proper drainage, and sloping the grade away from the foundation, your builder will ensure that the house is dry and stable for a long time.