A contractor wants to cut a hole in the side of our condo unit and run a three-inch pipe up above the roof line. Is it a necessity that this run up on the outside, or can it run up through the attic?
Scott County Iowa radon
As long as the pipe is properly sealed (and especially if the fan on the system is in the attic), the pipe can be run up through the house. It may be easier from a construction standpoint to go outside, but there is nothing (from a radon mitigation standpoint) that requires the pipe to run outside the house.
Some more discussion of this can be found at these sites: