10 will be capable of being completely enclosed such as by closing all windows and doors the ground under house 10 is gas permeable and in the preferred embodiment is a layer of crushed rock gravel or some other similar gas permeable aggregate 14 as shown in fig1 the invention consists of three basic parts a gas receiving network 20 a conduit means 30 and a venting means 40 an optional feature is a vacuum indicator means 50 gas receiving network 20 is shown in side view in fig1 and in bottom plan view in fig2 gas receiving network 20 is located below slab 12 at a depth sufficient so as to be beneath typical plumbing and electrical wiring the receiving network 20 is arranged in a pattern so as to efficiently draw air from all areas beneath the house 10 in the preferred embodiment gas receiving network 20 comprises at least one loop pipe 22 whose shape generally conforms to the perimeter of slab 12 and a number of feeder pipes 24a 24n which extend inward from loop pipe 22 to cover all areas under house 10 in the preferred embodiment all pipes are approximately four inches in diameter each feeder pipe 24a 24n is in communication with loop pipe 22 which may be accomplished by attaching one end to loop pipe 22 on the opposing end of each feeder pipe 24a 24n is a cap 26 loop pipe 22 and feeder.