I have seen multiple houses sitting on concrete basements or slabs where additions were added on to the house in the 1970s-80s and air flows directly from under the addition to inside the house. The additions are not on concrete slabs, they appear to be just on piles with a crawlspace between the floor of the addition and the dirt below. Air then seems to get sucked from the crawlspace into the house when the furnace runs.

Is this the correct way to do an addition? Would it be better to pour a concrete slab under the addition which is connected to the concrete slab the rest of the house sits on, and build on that? Would that eliminate this air flow?

There is high radon around here and it always concerned me that the air sucked in from under the addition probably results in much higher radon levels inside the house.

2 Answers 2


Radon emitted from soil can pass through concrete quite easily. Furthermore, concrete and other earth products themselves can emit radon as well.

The fresh air vent coming from under an addition will not be any better with or without a concrete pad if the radon source is not properly mitigated.

If you have a concern for radon exposure in your home the only practical solution is to have your home professionally tested and mitigated if necessary.


Perhaps what you are seeing are three-season porches. Which don't need foundations or basements.

Radon typically comes in through the foundations...it's in the earth....it isn't floating around in our air.

Although there are all kinds of 'studies' relating Radon to deaths and diseases, I don't believe there is a death certificate anywhere where the cause of death is Radon.

  • These are additions such as extending the side of the house out or adding new rooms. The added parts sit on piles, not a full foundation or slab as the original part of the house. As for radon I believe concrete slows/blocks its penetration vs. just dirt.
    – user35358
    Jul 22, 2020 at 15:41
  • There are also few death certificates where the cause of death is petrol, yet there would be many fewer automobile fatalities without it. Radon is an very serious concern and shouldn't be trivialized.
    – psaxton
    Jul 23, 2020 at 16:14
  • That is patently ridiculous. Petrol does not cause car accidents. Radon is a scare tactic used by salesmen to sell. But you are of course welcome to your opinion. Jul 24, 2020 at 15:39

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