Testing context

The device sat on the floor, or up near the ceiling

“It was on the floor in the corner, out of the way.”

Placement guidance specifies a height range because the intention is to measure the air people breathe rather than the air at the slab or against the ceiling.

Floor-level placement is the more common of the two and tends to read higher, since the source is below.

Why this matters

What it changes about the decision in front of you.

Concentration is not uniform floor to ceiling, particularly in a basement where entry is through the slab.
Height is recorded on a compliant placement note, so its absence is noticeable to anyone reviewing the result.

What it could influence

Where the effect is likely to show, and in which direction where that is knowable.

A floor-level reading is likely to sit above what a compliant height would have produced in the same room.
A device on a high shelf may read lower, though the effect is generally smaller than at floor level.

What this does not settle

What still stands. Noticing a problem is not the same as losing the evidence.

The measurement still demonstrates that soil gas is entering, which is the substantive finding.
A floor-level figure below a threshold is a reasonably reassuring result, since compliant placement would likely have read lower still.
It does not mean the device malfunctioned or that the laboratory figure is wrong.

What a professional is likely to ask

Worth having answers ready. None of these is a test you can fail.

The actual height, which is measurable now if the position is remembered.
Whether the surface was a floor, a shelf, or something suspended.
Whether a compliant position exists in that room for a repeat.

What you can check yourself

Things you can establish today, without anyone visiting.

The height of the position used, with a tape measure.
Whether furniture in the room offers a position in the specified range.

What genuinely needs somebody on site

Where this platform stops. These are not questions a website can answer about your house.

The vertical gradient in that specific room, which varies with the slab and the air movement.

Categories a next step could fall into

Unordered, and none of them is a recommendation. Which applies depends on things this page does not know about your situation.

Review the testing context

When it is considered. When the conditions, placement, or duration of the test are unclear, which is the most common situation and the cheapest to resolve.

What it would establish. Whether the existing result is something to reason from, or something to repeat under conditions that can be described.

Discuss another test

When it is considered. When the prior result is disputed, the conditions cannot be reconstructed, or a longer observation period would answer the question being asked.

What it would establish. A second reading under conditions someone can describe, which is what makes two numbers comparable rather than merely different.

Sources

U.S. EPA — A Citizen’s Guide to Radon

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