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Air Intrusion and Its Impact on Moisture
Transport in Mechanically Attached Roofing
Systems
Institute For Research in Construction
Authors: Suda Molleti, Bas Baskaran, Peter Kalinger
and Pascal Beaulieu
Presenter: Peter Kalinger
International Symposium 2011
Institute for Research in Construction
Outline
Overview of Air Intrusion
Quantification of Air Intrusion – Experimental
Testing
Impact of Air Intrusion on Moisture Transport –
Experimental Testing
Conclusions
Institute for Research in Construction
SCIENCE BEHIND AIR MOVEMENT
Pre
ssu
re D
iffe
ren
ce
Wind
HVAC
Temperature Flow Path
Institute for Research in Construction
When air enters or leaves from one environmental
condition to the other environmental condition through the building
envelope assembly, it is termed as “Air Leakage”.
AIR LEAKAGE
Institute for Research in Construction
When conditioned indoor air enters into a building envelope
assembly but cannot escape to the exterior environment, it is
termed as “Air Intrusion”.
AIR INTRUSION
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AIR LEAKAGE VS. AIR INTRUSION
RCI INTERFACE – NOVEMBER 2010 PROFESSIONAL ROOFING– JANUARY 2010
Institute for Research in Construction
WIND UPLIFT ACTION OF MECHANICALLY
ATTACHED ROOFING SYSTEM
WIND SPEEDS > 50 mph
MEASURED PRESSURES > 30 psf
RIALTO, CALIFORNIA
Institute for Research in Construction
AIR INTRUSION IMPACT ON MOISTURE
TRANSPORT
What is the relation between air intrusion and moisture transport
and what are the limits for potential condensation ?
Institute for Research in Construction
DYNAMIC ROOFING FACILITY AIR INTRUSION TEST FACILITY (DRF-AI)
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DECK INSTALLATION
36” 36” 24”
Deck Overlap
Edge Seal Along Width
Deck edges on L-channel
Edge Seal Along Length
L- lock Seam
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Additional
tests to fill
the data
NRCA/CRCA
SIGDERS DEVELOPED CONTROL
DATA FOR AIR INTRUSION
0.79
2.05
2.59
2.87
0.36 0.38 0.34
0
0.5
1
1.5
2
2.5
3
3.5 M
B-3
ft-N
oA
B
TP
-6ft
-No
AB
TP
-10
ft-
No
AB
TS
-10ft
-No
AB
MB
-3ft
-Wit
h S
AF
TP
-6ft
-Wit
h S
AF
TS
-10ft
-Wit
h S
AF
Rep
ort
ing
air
in
tru
sio
n v
olu
me
at
25
psf
(ft
3/l
ine
ar
ft)
WITHOUT AIR RETARDER WITH AIR RETARDER
Institute for Research in Construction
CRCA-NRCA RESEARCH PROJECT
MEMBERS
Task 1 – System Evaluation: Quantify air
intrusion of the common roofing assembly
configurations
Task 2 –Develop a relation between air
intrusion and risk for moisture
condensation
RESEARCH TASKS
August 2009 - August 2012 Project Duration :
Institute for Research in Construction
EXPERIMENTAL LAYOUT
Deck : 22 Ga -80 ksi
Membrane
EPDM
4 ft x 4 ft x 2 in. ISO
3.HD Cover Board
1.Kraft Paper
3 SYSTEMS TESTED
PVC
2.Polyethylene
Institute for Research in Construction
Mechanical
fastened
5/board = 50 fasteners
INSULATION INSTALLATION : S1 AND S2
10 boards
of
48 x 48 x 2 in
ISO
seals
along
the
width
ISO
seals
along
the
length
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S3 : HD COVER BOARD(NO AIR RETARDER ON DECK)
HD: = 4 FT X 8 FT X 0.5 IN
FD: = 8 PER BOARD
INSULATION INSTALLATION
2 FT
4 FT
4 FT
4 FT
4 FT 2 FT
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MEMBRANE LAYOUT
S1, S3: TS: FR = 114 IN FS = 12 IN.
S2: TP: FR = 66 IN FS = 12 IN.
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REPORTING AIR INTRUSION VOLUME AS PER THE ASTM D7586-11
0.79
2.05
2.59
2.87 2.81
0.36 0.38
0.65
0.34
1.03
0
0.5
1
1.5
2
2.5
3
3.5
MB
-3ft-N
oA
TP
-6ft-N
oA
B
TP
-10ft- N
oA
B
TS
-10ft-N
oA
B
TS
-10ft-W
ith C
B (S
3)
MB
-3ft-W
ith S
AF
TP
-6ft-W
ith S
AF
TP
-6ft-W
ith P
oly
(S2
)
TS
-10ft-W
ith S
AF
TS
-10ft-W
ith K
P (S
1)
Rep
ort
ing
air
in
tru
sio
n v
olu
me
at
25
psf
(ft
3/l
ine
ar
ft)
WITHOUT AIR BARRIER WITH AIR BARRIER
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TASK2:
AIR INTRUSION - MOISTURE TRANSPORT
EXPERIMENTAL STUDY WITH DYNAMIC PRESSURES
AND DIFFERENT RELATIVE HUMIDITY
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TEST SPECIMENS AND CONDITIONS
THERMOSET SYSTEM WITHOUT AIR RETARDER
S1: No Suction Pressure
(Vapor Drive) S2: With Suction Pressure
S3: No Suction Pressure
(Vapor Drive) S4: With Suction Pressure
Relative Humidity
25%
35%
50%
65%
THERMOSET SYSTEM WITH AIR RETARDER
Outdoor Target
Temperature:
-50C (230F)
Indoor Target
Temperature:
220C (720F)
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SUCTION PRESSURE
CSA A123.21 –DYNAMIC LOADING CYCLE
LEVEL 2200
CYCLES
Target Pressure: 60 psf
15 psf: 800 cycles
30 psf: 1100 cycles
45 psf: 225 cycles
60 psf: 75 cycles
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TYPICAL TEST SPECIMEN CONSTRUCTION
Temperature
And RH
sensors
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EXPERIMENTAL APPARATUS
Temp: 22°C
Humidity:
25 – 65 %
Temperature:-5°C
4ft x 4 ft
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TEST PROCEDURE Insulation boards pre weighed and the specimen constructed
Test chamber set to a target temperature of -50 C (230F)
Temperature and relative humidity set to 220C (720F) and 25% in the humidity
chamber.
After temperature and relative humidity stabilization, specimen subjected to
CSA A123.21-10 dynamic pressures for a duration of 5 hrs
Test stopped for visual inspections of condensation and insulation boards
weighed to measure the moisture content
Insulation boards put back and specimen reconstructed for testing at next
humidity level
With above outdoor and indoor temperatures, each specimen is subjected to
four different humidity levels of 25%, 35%, 50% and 65% and with dynamic
pressure application at each humidity level
Each specimen subjected to four days of testing (One humidity condition /day)
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25% 35 %
S1:NO AIR RETARDER - NO SUCTION PRESSURE VAPOR DRIVE
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BREACH IN
THE AIR
RETARDER
DURING
INSTALLTION
S4:WITH AIR RETARDER-WITH SUCTION PRESSURE
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S4:WITH AIR RETARDER-WITH SUCTION PRESSURE
RETESTED
65%
RH
50%
RH
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MOISTURE GAIN : COMPARISON
0
10
20
30
40
50
60
70
80
90
100
S1 S3 S2 S4
Mo
sit
ure
ga
in,
gm
Test Specimens
Board 1 Board 2 Board 3 Board 4
NO AB-NO SP AB- NO SP NO AB- SP AB- SP
0
1
2
3
4
5
6
7
8
9
10
S1 S3 S2 S4 Mo
sit
ure
Co
nte
nt
( %
of
DW
)
Test Specimens
Board 1 Board 2 Board 3 Board 4
Vapor Drive
Vapor Drive
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AIR INTRUSION LIMIT FOR POTENTIAL
CONDENSATION
0.79
2.05
2.59
2.87 2.81
0.36 0.38
0.65
0.34
1.03
0
0.5
1
1.5
2
2.5
3
3.5
MB
-3ft-N
oA
TP
-6ft-N
oA
B
TP
-10ft- N
oA
B
TS
-10ft-N
oA
B
TS
-10ft-W
ith C
B (S
3)
MB
-3ft-W
ith S
AF
TP
-6ft-W
ith S
AF
TP
-6ft-W
ith P
oly
(S2
)
TS
-10ft-W
ith S
AF
TS
-10ft-W
ith K
P (S
1)
Re
po
rtin
g a
ir in
tru
sio
n v
olu
me
at
25
ps
f (
ft3/l
ine
ar
ft)
Outdoor T : -50 C
Indoor T: 220 C
Indoor Humidity: 65%
WITHOUT AIR RETARDER WITH AIR RETARDER
Institute for Research in Construction
In collaboration with CRCA, NRCA and four major roofing manufacturers,
a research project focussing on air intrusion quantification and its impact
on the moisture transport was started.
The kraft paper and polyethylene sheet did minimize the air intrusion into
however both underperformed compared to the self adhered film as air
retarders.
Installing HD cover boards on top of the insulation provided no resistance
to air intrusion as the cover boards do not seal the primary flow paths of
the steel deck.
The risk for potential condensation and increased moisture gain within the
system from air intrusion is considerably higher than the potential moisture
gain due to vapour transmission.
CONCLUSIONS
Institute for Research in Construction
CONCLUSIONS
Air retarder at the deck level can minimize the moisture gain in the roof systems
both due to vapor transmission and air intrusion. However, trapped air due to air
intrusion between the air retarder and air barrier (membrane) within the roof
system can cause condensation.
At an outside temperature of -50 C (230F) and indoor conditions of 230C (720F)
with 65% relative humidity, an air intrusion volume of 0.63 ft3/ linear ft (17 L /
linear m) could be said to be the critical volume for potential condensation in
mechanically attached roofing systems.
Further study is needed to investigate and develop the limits for potential
condensation at different outdoor and indoor conditions, and at different humidity
levels.
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