Radon - one or two?

I’m scheduled to perform HI, WDI ( Wood Destroying Insect ), and Radon inspections on a duplex. The space below grade is a single shared crawlspace. Would you place a monitor on the first floor of each unit? I’m in PA, and I can’t seem to find any direction on this.


I would place a monitor on the 1st floor of each unit.

Charge for 2 tests (1 for each unit).

Thanks Joe. I already quoted for one, but I’ll place two and correct on my next opportunity.

My understanding is that RE transactions require TWO. For accuracy anyway its best. 48hr Minimum.

I have to agree with Joe, EPA and NRSB protocols recommend the lowest habitable spaces be tested.



I always use two for testing as well. The readings are usually different even in the same area. Kind of strange.IMO.

Are we talking charcoal canisters or electronic moniters. If cannisters, then 2 are required to be placed within 6" of each other. If an electronic moniter, only one- but I would place one in each unit.


We’re talking Sun Nuclear CRM’s. I decided to place one in each unit, and call the event a “duplcate measurement” which is required by PA DEP. Thanks for your input.


I had assumed you were referencing Sun Nuclears seeing that you are PA State licensed in that testing category.

When in doubt, add an extra CRM monitor.

The data recorded always provides good reference info.

Are you using the 1027’s?

Ya know, it constantly amazes me how many people here in Kentucky are providing radon testing without having any training or certification.

And most of them are NACHI members!!!

My opinion is that if you do not know EPA protocol’s then why in the hay are you selling yourself as an inspector that knows how to test for radon!
Do you need a picture of a termite run also?

I use (2) Charcoal Bags on a custom made hanger in the lowest habitable level.

With a CRM, only a single device is needed. All others (including e-perm), require two. These are for Real Estate transactions.

NJ only requires a single device for radon resting, regardless of type, for all Real Estate transactions.

In rental units such as the duplex mentioned I always upsold to doing each. The reason was liability. Unless your a geologist and know the rock strata below the building it is nearly impossible to predict a reading in a particuliar unit.

In a townhouse complex I saw a number of other units with extraction systems and stated to my client that I was pretty certain that his unit had radon but the reading came back under 3.5 picocurries. He called me on it and my only reply was that his future neighbors were doing such as good job extracting it that he wouldn’t have to!

With Radon you can never be certain unless you test.


EPA Protocol
3.3 Measurement Location

[FONT=Tahoma]EPA recommends that measurements made for a real estate transaction be performed in the lowest level of the home which is currently suitable for occupancy. This means the lowest level that is currently lived-in, or a lower level that is not currently used (such as a basement, which a buyer could use for living space without renovations). Measurements should be made in a room that is used regularly, such as a living room, playroom, den, or bedroom. This includes a basement that can be used as a recreation room, bedroom, or playroom. This provides the buyer with the option of using a lower level of the home as part of the living area, with the knowledge that it has been tested for radon.[/FONT]

The reason for placing the radon test in the lowest livable space is to get the “worst” case reading. Don’t forget, when placing Radon tests, the building must meet closed building conditions for the 12 hrs prior to the test and throughout the entire 48hr test period to get valid results. In a Real Estate transaction, 2 tests are placed side by side at 4" apart in the lowest livable space unless you are using a CRM then only 1 is required. The other tests are not supposed to be placed in different locations unless you are placing 2 at each location. (there is another option, but not normally used due to time factors)

Testing location for an existing owner not selling may be different than for a real estate transaction.

For all that are testing for Radon and are not Certified for doing so or do not know proper EPA protocol, visit http://www.epa.gov/radon/pubs/homes_protocols.pdf
Following EPA protocol will result in more accurate results for your clients and better protect you.

Happy testing.


Revised info link: http://www.epa.gov/iaq/radon/pubs/

I’m always running into people who want to finish an unfinished basement after they buy the house. They want to know the Radon levels in the unfinished basement.

I advise them of the protocol, tell them about sealing the slab perimeter and penetrations, tell them levels will be effected by changes they’ll make when finishing the basement… and then I test in the unfinished basement. They’re paying for testing of their main area of concern.

I’ll test any area someone wants tested, but I’ll do my best to educate them before agreeing to the placement location.

Tell me about sealing slab perimeter and penetrations of an unfinished basement.

Radon gas rises into the living space through any opening it can find, such as the perimeter cold joint where the slab meets the foundation wall and through boxouts placed in various areas of the slab for plumbing pipe stub-outs and waste/drain lines (although seems like sometimes they just pour around them).

Anyway, caulking the perimeter joint and caulking and sealing any penetrations or boxouts in the field of the slab should take the levels down some.

If they were high to begin with or just barely acceptable, when the ground freezes around the home exterior, radon levels in the basement may rise to unacceptable levels, since the unfrozen ground beneath the slab provides an path for the gas to rise. If this is the situation, mitigation to acceptable levels may require an active system.