A Field Study of Full Height Passive Radon
Stack in the National Capital Region of
Canada
Prepared by: Dr. Liang Grace Zhou, Ethan Li, Gang Nong, and Jeff Whyte
National Research Council Canada - Construction Research Centre
For: the 14th International Workshop on the Geological Aspects of Radon Risk
Mapping
February 7, 2019
Radon Reduction Methods
2
(EPA Consumer’s Guide to Radon Reduction, 2016)
• Active sub-slab depressurization 50-99%
• Passive sub-slab depressurization 30-70%
Maybe more efficient in cold climates• Sub-membrane depressurization 50-99%
• Sealing radon entry routes Variable
• Sump-hole suction 50-99%
• Drain tile suction 50-99%
• Basement pressurization 50-99%
• Heat recovery ventilation Variable
3
2014 British Columbia Provincial Building Code
Radon Pipe Changes
(Illustration courtesy of BC Office of Housing and Construction Standards)
In 2015, several change requests submitted to
National Building Code (NBC) Standing
Committee on Housing and Small Buildings.
Installation of a radon vent pipe which extends
through, and terminates outside, the building in
Radon Area 1.
Passive Radon Stack Radon Reduction Effectiveness
Canadian Centre for Housing Technology Passive stack 56 Bq/m3No stack 85 Bq/m3
Passive Stack Radon Reduction: 35%
R14 insulation in attic to avoid ice blockage
Passive Stack:
Insulation in Unheated Space
5
R7 in unheated attic and R14 above rooflineCanadian General Standards Board Radon Control
Options for New (149.11) and Existing (149.12)
Buildings
Computational Fluid Dynamics Simulation Using COMSOL Multiphysics
Outdoor T: -25 °C and -30 °C
Attic T: -13 °C and -17 °C
Stack Inlet T: 18 °C
Stack Inlet RH: 50% and 100%
Stack Air Speed: 0.05 m/s, 0.1 m/s and 0.15 m/s
Above Roof Wind Speed: 21.5 km/h
6
Full Height Passive Radon Stack:
A Field Study in the National Capital Region
Why:
• Mid-term radon monitoring to minimize bias;
• A wide range of measurement parameters to understand system performance;
• Address National Building Code change requests;
• Develop practice guide.
How:
• 5 homes in Ottawa-Gatineau;
• House characteristics survey questionnaires;
• Blower door test before and after stack installation for air tightness;
• Tracer gas decay test before stack installation for natural air exchange rate;
• >30 day stack open, >30 day stack closed in the fall of 2017;
• >30 day stack open, >30 day stack closed in the winter of 2018;
• Measurements: radon concentration (indoor, soil, and stack); sub-slab pressure;
P/T/RH at the base and the exit of the stack; flow rate and air speed in the stack.
Special thanks to:
MB Radon Solutions for the stack installation and sub-slab communication testing
Jonathan Ham Energy Consulting for the blower door testing and locating leaking points
7
Full Height Passive Radon Stack:
House Characteristics Questionnaire
• 4 single homes and 1 townhome were recruited;
• All homeowners understood what radon is and the associated health risk;
• The highest level of education in all 5 households was university level or
higher;
• 1 home was located on a 2 acre property with minimal obstructions, and
the other homes were located in areas of moderate housing density;
• 4 homes were 2 storeys with a basement, and1 home was a bungalow
with a basement;
• All 5 homes had forced air furnaces and air conditioning systems. Only 1
home had a Heat Recovery Ventilator (HRV);
• Only 1 home had a smoker.
8
Full Height Passive Radon Stack:
Tracer Gas Decay Tests and Natural Air Exchange Rate
Home ID
Square footage
excluding the
basement (ft2)
Air Changes per Hour (ACH)
1 2000 0.071
2 1400 0.493
3 2100 0.046
4 2000 0.096
5 2950 0.101
y = 3.5933e-0.493x
R² = 0.9723
0
0.5
1
1.5
2
2.5
3
3.5
0 1 2 3 4
SF6
co
nce
ntr
atio
n (
pp
m)
Elapsed time (hour)
Home 2 SF6 Decay
y = 0.5675e-0.046x
R² = 0.8874
0
0.1
0.2
0.3
0.4
0.5
0.6
0 1 2 3 4 5 6
SF6
co
nce
ntr
atio
n (
pp
m)
Elapsed time (hour)
Home 3 SF6 Decay
9
Full Height Passive Radon Stack:
Blower Door Test and Sealing Radon Entry Points
10
Full Height Passive Radon Stack:
Radon in Soil Gas Sampling
• Saphymo soil gas probe
• AlphaGUARD PQ2000
PRO radon monitor
• AlphaPUMP
• Saphymo Multisensor Unit
• Vapor Pin™ KitHome ID
Number of
sampling
locations
Average
sampling depth
(m)
Soil radon
concentration
(Bq/m3)
1 20.50 36100
0.50 58200
2 1 Sub-slab area* 22560
3 6
0.81 15690
0.65 22512
0.51 11780
0.50 11470
0.60 12320
0.50 19240
4 5
0.93 18740
1.00 21550
0.77 36120
0.80 28590
0.75 34650
5 1 0.50 57050
• Difficult to drill 0.8-1.0 m
deep into the ground
• Difficult to obtain sufficient
soil gas flow due to high
back pressure in the
compact soil
• Radon concentration in
soil varies greatly over
small distances
11
Full Height Passive Radon Stack:
Communication Test and Stack Insulation
Sub-slab Pressure Communication Testing is critical! No stack installed in Home 5
due to unsuccessful sub-slab pressure communication testing
R7 in unheated attic and R14 above roofline
12
Home 1 Home 2 Home 3 Home 4
Full Height Passive Radon Stack:
Stack Configuration
13
Results from Home 1 Closed stack: 150 Bq/m3 Open stack: 110 Bq/m3 (Reduction 36%)
Before
sealing
radon entry
points: 310
Bq/m3
Stack height = 23 ft
Flow rate = 2.4 cfm
14
Results from Home 2 Closed stack: 165 Bq/m3 Open stack: 12 Bq/m3 (Reduction 92%)
Before
sealing
radon
entry
points:
200 Bq/m3
Stack height = 31 ft
Flow rate = 11 cfm
15
Results from Home 3 Closed stack: 117 Bq/m3 Open stack: 22 Bq/m3 (Reduction 81%)
Before
sealing
radon
entry
points:
196 Bq/m3
Stack height = 31 ft
Flow rate = 12 cfm
16
Results from Home 4 Closed stack: 140 Bq/m3 Open stack: 68 Bq/m3 (Reduction 51%)
Before
sealing
radon
entry
points:
161 Bq/m3
Stack height = 23.5 ft
Flow rate = 3.4 cfm
17
Full Height Passive Radon Stack Field Study:
Observations and Conclusions
• A monitoring period of 4 weeks for each testing scenario is required to capture
passive radon stack performance;
• Under the test conditions, the 4 passive radon stacks reduced the indoor
radon concentrations by 36%, 92%, 81%, and 51%;
• Height of passive radon stack is critical (>25 ft to achieve >50% reduction);
• Blower door testing plus a smoke pencil can pin point the radon entry points;
• Sealing radon entry points effectively may contribute significantly to radon
reduction;
• Insulation of the portion of stack passing unheated space may enhance the
stack effect and radon reduction;
• Radon mitigation requires specific knowledge and skills as well as good
practice;
•Tracer gas decay test demonstrated Home 1 had <0.1ACH; a HRV and
increased ventilation rate may be a radon solution;
• Soil gas radon levels can vary within a very short distance and thus sampling
radon from soil provides limited extra value.
18
Future Work: 2018 and Beyond
Phase II of field study of full size passive radon stack in BC (15 homes):
• House characteristics questionnaire;
• Conduct blower door testing prior to open/closed stack testing;
• >30 day stack open, >30 day stack closed in the fall of 2018
• >30 day stack open, >30 day stack closed in the winter of 2019
• Measurements: radon concentration (indoor and stack); sub-slab pressure;
P/T/RH at the base and the exit of the stack; air speed in the stack.
A field study of HRV for indoor radon control in airtight houses with moderate
radon levels
1919
Thank you
Liang Grace Zhou
Senior Research Officer
613-990-1220
www.nrc-cnrc.gc.ca
November is Radon Action Month in Canada!
20
Outreach
• “Radon in Canadian Buildings”, Building Owners and Managers Association of Ottawa,
2012
• “Radon Mitigation NRC’s Indoor Air Strategies and Solutions,” for Association of
Municipalities of Ontario, 2013
• “Impact of Radon ASD System on Re-entrainment, Energy Use, and Indoor
Environment”, Construct Canada Expo, Toronto, 2013
• “New Research for Healthier Homes,” Better Builder Magazine, 2014
• Canadian Home Builders’ Association Housing Research Summary 2013–2015
• Host a stakeholder consultation workshop in 2012
• “NRC helps integrate radon technology into the building code”, Canadian Association of
Radon Scientists and Technologists, Vancouver, 2015
• “Experimental Study Of Heating Energy Use And Indoor Environment During Operation
Of Active Soil Depressurization Radon Mitigation System”, Indoor Air Conference,
Belgium, 2016
• “NRC and Radon Control Technologies”, Federal Provincial Territorial Radiation
Protection Committee 2016
• “NRC and Radon Control Technologies”, CHBA TRC Forum 2016
• “Combatting Radon with Scientific Research”, Construct Canada Magazine in 2017
• Media launch of National Radon Action Month 2017
21
Home ID Test Scenario ACH @50 Pa ELA (sq.in.)
1
Before stall
installation5.17 179.8
After stack
installation5.00 169.0
2
Before stall
installation6.02 174.9
After stack
installation4.94 135.9
3
Before stall
installation3.30 146.4
After stack
installation3.39 167.3
4
Before stall
installation3.80 200.7
After stack
installation3.90 213.5
5
Before stall
installation1.97 65.6
After stack
installation
(No stack installed)
-- --