MITIGATION APPROACH ON REDUCING
THE NEUTRAL PRESSURE PLANE
STAND-ALONE OR COMBINED WITH OTHER METHODS
Georges A. Roserens
Swiss Federal Office of Public Health,
Radiological Risk Section,
CH-3003 Bern, Switzerland

ABSTRACT
Radon risk reduction requires that mitigation systems should be cost-effective. Standard
mitigation systems are well known, such as ASD, PSD, sealing, etc. Under natural conditions,
the ground floor is subject to negative air pressure and the upper story to positive pressure.
Such conditions are conducive to high radon concentrations as they encourage infiltration of
the gas into the building through cracks, fissures and passages in the basement. Mitigation by
reducing the neutral pressure plane is a simple method to reduce the radon concentration. To
lower the neutral axis, we install small wall ventilators or passive ventilation through pressure
differential balancing (in the window or in the wall). This method could also increase the
efficacy of all other remediation systems.

INTRODUCTION
The neutral pressure plane is variable and depends on the
inhabitant's behavior and the building type.. In Switzerland high
radon concentration up to 1,000,000 Bq/m3 or 27,000 pCi/l at a
depth of 3 meters in the soil has been measured.
(Johner H. U. and Roserens G. A.1998).

Radon entry routes: cracks, holes and gaps are vs: diffusion, water, buildings material,
almost the major contributor to the radon concentration in dwellings. The quantity of air
mixed with radon passes through a fissures or openings is mathematically complex to
determine.
1

& 2 #2
qV (inf =C d A$ 'p !
%) "

n

qV "inf =C inf (!p )

An important point to bear in mind, however, is that this quantity is related to the difference
in pressure.

307

HVAC - HRV AND RADON
Test and adjust your HVAC system.
Depressurization should be avoided (more radon fx(Δp) and risk of backdrafting).
If the building uses an HVAC system, it is necessarily to adjust it and reduce the negative air
pressure or better to tend to have a slightly positive pressure 0 to1 Pa (0-to 0.00014 psi).

MORE OR LESS AIRTIGHT HOUSES - WITHOUT HVAC - HRV
Energy saving: buildings have an airtight shell. This prevents
warm air from escaping and cold air from entering the home.
The external envelope of a building should be as airtight as
possible.
Energy efficient house: make it airtight.
For standard new houses measured: ca. 0.15 ACH
Blower Door test for new green buildings: max. 0.6 ACH
at 50 Pascals differential pressure

neutral
pressure plane

after
Natural ventilation:
If you open a window at the lowest position you will lower the
before
neutral pressure plane. You can not justify the radon reduction
with the dilution effect. In fact lowering the neutral pressure
axis is much more important (reducing the vacuum effect). In winter the owners would open
the window only few minutes daily, it is not enough to see a radon reduction in average.
Drill a hole in the external wall, but you will get an uncontrolled quantity of air and cold,
depending on the orientation of the wall, the wind etc.. (an unacceptable situation).
To regulate the air quantity to lower the neutral axis, we use a small fan, blowing from
outside to inside to control the air flow quantity (not to be confused with the house
pressurization).

308

The airflow is managed between outside and inside. In the winter time it is not imperative to
warm up the cold air because the quantity is minimal and sufficient to equilibrate the pressure
difference.
In many cases is also possible to install a simple grill in the window or in the wall to reach the
same effect. Noise and dust: use a device with sound insulation to reduce the outside noise
and an air filter.

REDUCING THE NEUTRAL PRESSURE PLANE
COMBINED WITH OTHER METHODS
This method increases the effect of traditional mitigation such as: active soil
depressurization, passive soil depressurization, crawlspace depressurization, crawlspace
airing, hollow floor depressurization, hollow wall depressurization and basement
depressurization.

CONCLUSIONS
Throughout the world, houses are different, climate is not the same and behavior may play an
important role. It is very important to pursue and to analyze alternatives and to test the limits
of these other possibilities. The focus is on developing low-cost mitigation systems.

309

310

311

WITH A WALL FAN WHEN JUST ONE AREA NEEDS TO BE
REMEDIATED

3

(20-60m /h preheating not necessary)

Fan switched off,
vanes closed fermés

312