A Radon Mystery on a Home Inspection in Nassau NY

A Home Inspection I performed in Nassau NY


A unique radon issue we encountered.

I wanted to write a blog about a radon situation I encountered on a property that I performed a home inspection on in Nassau New York. At the initial home inspection, we tested for radon levels. The property already had a radon mitigation system installed that appeared to be working perfectly.

Our radon levels came back high approximately 12.0, so the owner called back the radon mitigation company that put the radon system in 10 years ago to further assess. The radon mitigation company installed an additional suction area to pull the radon gas below the slab from a seperate and distinct area to see if that would solve the problem.


Two more tests were done one electronic and one with charcoal canisters to determine if the radon levels were resolved and reduced to a normal level. Both radon tests returned very high results almost as if the radon mitigation system was never installed.



The owner and the radon mitigation company started to brainstorm to try abs figure out why the radon levels were still high. The radon mitigation company ended up sealing the very small cracks on the slab as the radon can leak into the basement from the small slab cracks. After they sealed the cracks they tested for radon one more time. A radon test was done and the normals were in fact still high.


After a few days the buyer requested that a radon test was done to determine if the radon levels in the water were normal. The buyer was concerned about the radon within the well water.


Shield Guard Home Inspections returned to the home to take water samples. As I was in the home collecting water samples I was curious to see what was going on in the basement with the radon issue. As I was standing in the basement I started to think there has to be a way the radon is leaking into the basement through a decent size opening.


The basement was a poured foundation with a typically newer slab. The basement contained reflective insulation on the walls, covering all penetrations. I started snooping around and peeling back some of the insulation that was in the basement.


The basement was finished with foil faced insulation. I started to think about the penetrations in the foundation that may allow radon to leak inside. The two that popped in my head were the water supply line and the main drain line that went out to the road.


I identified where the main drain was exiting the foundation and it was covered with insulation. I peeled back the foil faced insulation and long and behold the white PVC pipe that was used for the main drain had an approximate 2 - 3” inch gap around the entire pipe.







Additionally the dryer was right near the main drain. The dryer was pulling air from that opening as the dryer can create negative air pressure as it runs its cycle. This means it could contribute to pulling in air and radon from the small foundation hole.



The radon mitigation company returned to the property in Nassau New York and sealed the 2 inch opening around the main drain pipe. A radon test was performed by our home inspection company and the test returned readings of 1.7 PCL. Readings under 4.0 PCL are considered “normal” .


Radon is a odorless gas that makes its way into the structure through the basement. Radon can seep into the basement through cracks, sub pump pit openings, penetrations and other openings around the basement walls and slab. Sealing the openings in the concrete walls and concrete slab can significantly reduce the amount of radon that enters the structure. Additionally you may be able to save money if you seal the openings around the walls and slab and avoid putting in additional suction points in the basement for the radon mitigation system if a radon mitigation system is recommended by a home inspection company.

Call us if you have any questions or would like to book a radon test or home inspection!


(518) 649-9111

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