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© buildingscience.com
Monitoring of Two Unvented Roofs
with Air-Permeable Insulation
in Climate Zone 2A
Kohta Ueno
Joseph W. Lstiburek, Ph.D., P.Eng.
December 5, 2016
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 2
© buildingscience.com
Unvented Roofs:
Background
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 3
© buildingscience.com
Unvented/Cathedralized Roofs
Insulation at roof deck, rather than attic floor
Brings HVAC ductwork/equipment into conditioned space
Can improve airtightness (ceiling plane vs. roof)
Wind driven rain, hurricane roof tear-off
Moisture risks with unvented roofs (vs. vented)
Condensation of interior moisture at roof sheathing
Code-compliant (IRC§R806.4) roofs—“air impermeable
insulation” (spray foam/SPF, exterior insulation)
Current research: air permeable insulation, CZ 2A
Lower cost, environmental impacts of SPF
Houston and Orlando test houses
Can moisture risk be managed?
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 4
© buildingscience.com
Why Unvented + Fibrous Risky?
Different than walls?
Moisture risks at sheathing
Interior-sourced air leakage
Vapor contributing too?
Zero-perm exterior (“wrong
side perfect vapor barrier”)
Night sky radiation cooling
Stack effect in winter
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 5
© buildingscience.com
2000’s Cathedralized Roofs-TX & FL
Houston climate (CZ 2A)
had moisture at ridge
Concentrated only at
ridge—rest of roof OK
Similar problems in
Jacksonville FL (CZ 2A)
No interior air/vapor
control (not practical)
Possible solution:
allowing release of
moisture at ridge?
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 6
© buildingscience.com
Test Site &
Instrumentation Setup
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 7
© buildingscience.com
Unvented Roof Test Houses
Houston: asphalt shingle, #30 paper
Unoccupied model, humidified in winter 3 of 3
Orlando: concrete tile, self-adhered membrane
Occupied by family of 4, 2 winters of data
Houston Orlando
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 8
© buildingscience.com
Unvented Roof Test Houses-Insulation
Houston: adhered fiberglass, R-38/RSI 6.7
Orlando: netted/blown fiberglass R-38/RSI 6.7
Vapor open insulation: 120 perm-in. or
170 ng/(Pa·s·m)); no interior vapor control layer
Houston Orlando
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 9
© buildingscience.com
Diffusion Vent (Houston)
200+ perms diffusion vent
Roofsheathing
2-in. holes at 2-3 ft. of hip
Tape for air & water barrier continuity
Ridge slot opening
Vapor-permeableridge membrane
Ridge vent
Asphalt shingles
30# felt underlayment
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 10
© buildingscience.com
Diffusion Vent (Orlando-Tile)
Tape for air & water barrier continuity
Ridge metal & cap tile
Vapor-permeableridge membrane
Ridge slot opening
Roofsheathing
Concrete roof tiles
Self-adhered roof membrane
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 11
© buildingscience.com
RIDGE
RIDGE
RID
GE
RID
GE
RID
GE
VALLEY
HIP
HIP
HIP
HIPHIP
HIP
HIPH
IPVALLEY
VALLEY
VA
LLEY
VALLEY
Sensor Key:
Relative humidity/temperature
Moisture content/temperature
Ridge “package”
UNVENTED
UNVENTED
ATTIC T/RH W (HIGH/LOW)
DV1 UV1
UV2 DV2
DV3
DV4
DV5
ATTIC T/RH N (HIGH/LOW)
ATTIC T/RH S (HIGH/LOW)
Roof Instrumentation (Houston)
Unvented
(membrane)
control vs.
diffusion vent
experimental
Ridge packages
Hip packages
“Downhill”
sensors
Interior T/RH
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 12
© buildingscience.com
Roof Instrumentation
Temperature, relative humidity
(RH), wood moisture content (MC)
“Wafer” sensors
Sensor Key:
Relative humidity/temperature
Moisture content/temperature
Moisture content wafer
Ridge wafer & T/RH
Sheathing Top MC/T
Upper MC/T
Ridge top MC/T
Upper MC/T
2'-0"
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 13
© buildingscience.com
Air Leakage Testing
Guarded testing:
some attics tight,
others noticeably
leaky
Depressurization
w. infrared
Air leakage
occurs at roof-
wall connections,
not field of roof
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 14
© buildingscience.com
Results: Houston
(Asphalt Shingle)
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 15
© buildingscience.com
Houston Attic Conditions (Summer)
Temperature tracks interior main space T
Warmer summer, cooler winter (ΔT 5-7 F/3-4 C)
Temperature high-low stratification
Dewpoint shows diurnal adsorption/desorption
from sheathing, dewpoint stratification
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 16
© buildingscience.com
Houston Unvented Peak Conditions
Strong seasonal swing in moisture levels
Wet in winter, dries out in summer
Interior humidification→major effect, high risk
Winter 1
Construction
MoistureWinter 2
Unoccupied
model
Winter 3
Humidified
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 17
© buildingscience.com
Houston Diffusion Vent Peak Conditions
MCs only risky in 3rd humidified winter, drier than UV
Ridge RH shows minimal seasonal swing →
coupled to exterior conditions
Humidified winter ~40-65% RH interior attic
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 18
© buildingscience.com
Houston UVR vs. DVR Comparison
Diffusion vent wetter in summer, but well within
safe range
Wintertime diffusion vent prevents accumulation
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 19
© buildingscience.com
0
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100
UVR1 UVR2 DVR1 DVR2 DVR3 DVH4 DVH5 DVR6
Re
lati
ve H
um
idit
y (%
)
0
5
10
15
20
25
30
UVR1 UVR2 DVR1 DVR2 DVR3 DVH4 DVH5
Waf
er
Mo
istu
re C
on
ten
t (%
)
Houston Ridge RH and Wafer Box Plots
RHs all have peaks 95-100%; diffusion vent roofs
higher RHs in summer
Wafer sensor shows long-term accumulation
UVR1 & DVH5 wafer wettest outliers
Box = upper/lower quartile
Whiskers = max/min
Ridge RH Sensor Ridge Wafer Sensor
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 20
© buildingscience.com
Results: Orlando
(Concrete Tile)
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 21
© buildingscience.com
Orlando Attic Conditions (Summer)
Dewpoint diurnal cycling
Highest dewpoints consistently at “high” locations
Interior DP higher than exterior DP at peaks
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 22
© buildingscience.com
Orlando Unvented Peak Conditions
Very high RHs and MCs first winter (construction
moisture); missing data after drywalling
Second winter—100% RH peaks, but sheathing
MCs not as concerning
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 23
© buildingscience.com
Orlando Diffusion Vent Peak Conditions
Diffusion vent: lower MCs, RH peaks
“Smear” RH data at ridge vs. unvented
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 24
© buildingscience.com
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100
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11/1/14 12/31/14 3/1/15 4/30/15 6/29/15 8/28/15 10/27/15 12/26/15 2/24/16 4/24/16
Rel
ativ
e H
um
idit
y (%
)
Mo
istu
re C
on
ten
t (%
)
UVR1 Peak Wafer DVR1 Peak WaferDVR1 RH UVR1 RH
Orlando UVR vs. DVR Comparison
Again, wafer and ridge RH patterns show safer
behavior with diffusion vent, less accumulation
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 25
© buildingscience.com
0
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UVR1 DVR1 DVR2 DVR3 DVH1 DVH2 RW1 RW2
Re
lati
ve H
um
idit
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)
0
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25
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35
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UVR1 DVR1 DVR2 DVR3 DVH1 DVH2 RW1 RW2
Waf
er
Mo
istu
re C
on
ten
t (%
)
Orlando Ridge RH and Wafer Box Plots
Unvented roof (UVR1) outlier, 100% RH; 35% MC
Diffusion vent roofs higher RHs in summer
Wafer sensor shows long-term accumulation
DVH2, RW1, RW2 wetter than other DVs
Box = upper/lower quartile
Whiskers = max/min
Ridge RH Sensor Ridge Wafer Sensor
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 26
© buildingscience.com
Orlando Roof Shading Patterns
Higher RH areas in shade (DVH2, RW1, RW2)
DVH2
DVH1
RW1
RW2
DVR3
N
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 27
© buildingscience.com
Decommissioning &
Disassembly
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 28
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Unvented Roof Disassembly/DV Retrofit
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 29
© buildingscience.com
Houston Hip Diffusion Vent
Monitored results showed low drying—closer to
unvented behavior vs. diffusion vent
Limited drying available at 2” hole “diffusion ports”
Covered up by asphalt shingles
Shingles cut back-retrofit
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 30
© buildingscience.com
Orlando Roof Peak Conditions
Spotting on netting near ridge, ~4 ft./1.2 m down
Worst issues at unvented (not diffusion vent):
Spotting on truss vertical member/king post
Spotting on upper T/RH sensor jacket, not lower
Water stains on ceiling drywall under ridge
First winter construction moisture condensation
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 31
© buildingscience.com
Orlando Attic Vertical Measurements
Handheld T/RH probe
Late afternoon June 2016
Temperature and dewpoint
differences w. height
-10
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70
80
90
50 60 70 80 90
Hei
ght
(in
.)
Temperature/Dewpoint (F)
Temperature (F)
Dewpoint (F)
-10
0
10
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30
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50
60
70
80
90
50 60 70 80 90
Hei
ght
(in
.)
Temperature/Dewpoint (F)
Temperature (F)
Dewpoint (F)
-10
0
10
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30
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50
60
70
80
90
50 60 70 80 90
Hei
ght
(in
.)
Temperature/Dewpoint (F)
Temperature (F)
Dewpoint (F)
Upper Attic Upper Attic Lower Attic
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 32
© buildingscience.com
Conclusions &
Recommendations
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 33
© buildingscience.com
Houston/Orlando Results
Diffusion vent avoids wintertime ridge
accumulation problems (ridge peak RHs/MCs)
No failures at low interior RH, bigger difference at
higher RH (interior humidification)
Airtightness disappointing in some cases-no SPF
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10/1/14 1/9/15 4/19/15 7/28/15 11/5/15 2/13/16
Re
lati
ve
Hu
mid
ity
(%)
Mo
istu
re C
on
ten
t (%
)
DVR1 Peak Wafer UVR1 Peak Wafer
DVR1 Peak RH UVR1 Peak RH
Unvented
Dif. Vent.
Dif. Vent.
Unvented
Summer WinterWinter
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 34
© buildingscience.com
Questions?Kohta Ueno
kohta [at] buildingscience [dot] com
Project Partners/Sponsors: Cosella Dörken, David Weekley
Homes, DuPont Building Innovations, Johns Manville, and
Owens Corning
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 35
© buildingscience.com
Document Resources Building Science Digest 149: Unvented Roof Assemblies for All Climates
http://buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates
Building Science Insight 043: Don't Be Dense—Cellulose and Dense-Pack Insulation
http://buildingscience.com/documents/insights/bsi-043-dont-be-dense
Building Science Insight 088: Venting Vapor
http://buildingscience.com/documents/insights/bsi-088-venting-vapor
Building America Report 1511: Field Testing of an Unvented Roof with Fibrous Insulation, Tiles,
and Vapor Diffusion Venting
http://buildingscience.com/documents/building-america-reports/ba-1511-field-testing-unvented-
roof-fibrous-insulation-tiles-and
Building America Report 1409: Field Testing Unvented Roofs with Asphalt Shingles in Cold and
Hot-Humid Climates
http://buildingscience.com/documents/building-america-reports/ba-1409-field-testing-unvented-
roofs-asphalt-shingles-cold-and
Building America Report 1001: Moisture-Safe Unvented Wood Roof Systems
http://buildingscience.com/documents/bareports/ba-1001-moisture-safe-unvented-wood-roof-
systems/view
Building America Report 1308: Moisture Control for Dense-Packed Roof Assemblies in Cold
Climates: Final Measure Guideline
http://buildingscience.com/documents/bareports/ba-1308-moisture-control-dense-packed-roof-
assemblies-cold-climates/view
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 36
© buildingscience.com
Reserve Slides
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 37
© buildingscience.com
Ventilated Attics—Best Choice
Roof sheathing dries to
ventilated attic-moisture safe
Interior moisture (air leaks)
ventilated away in winter
Air sealing at ceiling critical for
best performance (e.g., spray
foam air barrier, detail with
sealant)
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 38
© buildingscience.com
Then Why Unvented Roofs?
Living space built into roof
Vented cathedral assemblies—
often poor performance
Complicated rooflines, hip
geometries—how to vent?
Unworkable air barrier at
ceiling line
Blown-in rain (coastal)
Hurricane tear-off
HVAC in vented attic
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 39
© buildingscience.com
Ducts in unconditioned attic = huge energy losses
Industry reluctant to move ducts out of attic
Ice dam issues due to duct losses
Solution: bring ducts into conditioned space
Unvented/conditioned attic—keeps ductwork in
conditioned space, duct leak issues eliminated
Unvented Roofs & HVAC Placement
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 40
© buildingscience.com
Fibrous Insulation Unvented Roofs
Dense pack insulation of unvented roofs common
in cold-climate retrofits
Moisture risks (see BSI-043 “Don't Be Dense—
Cellulose and Dense-Pack Insulation”)—2 in 10 failure?
Violates I-codes (see IRC§R806.4)
“Ridge rot”—localized problems (SIPS same problem)
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 41
© buildingscience.com
Spray Foam/Exterior Insulation Roofs
2006 IRC: R806.4 Unvented attic assemblies
Minimum R-value of “air impermeable insulation”
Not ratio of R-values… don’t get me started…
Nail base needed with rigid foam on roof deck
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 42
© buildingscience.com
Why Fibrous Fill Unvented Roofs?
Unvented roofs without spray/board foams could
reduce costs and increase market penetration…
IF moisture damage risks are addressed
Retrofit opportunities (existing uninsulated living
space at roof line, without removing finishes)
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 43
© buildingscience.com
Why Unvented + Fibrous Risky?
Risk reduced by:
Airtightness of ceiling
Dense insulations-less
airflow
Solar drive
But white roofs, shading
Lower interior RH (winter)
Why many of them work?
Lower permeance interior
Assumes good airtightness—
vapor retarder not bypassed
Moisture accumulation:
what gets in vs. gets out
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 44
© buildingscience.com
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lati
ve
Hu
mid
ity
(%)
Mo
istu
re C
on
ten
t (%
)
DVR1 Peak Wafer UVR1 Peak Wafer
DVR1 Peak RH UVR1 Peak RH
Houston UVR vs. DVR Comparison
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ity
(%)
Mo
istu
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on
ten
t (%
)
DVR1 Peak Wafer UVR1 Peak Wafer
DVR1 Peak RH UVR1 Peak RH
Summer (August) Detail-5 Days
Winter (February) Detail-5 Days
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 45
© buildingscience.com
Results: Inward Vapor
Drive Experiment
(Houston)
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 46
© buildingscience.com
Sensor Key:
Relative humidity/temperature
Moisture content/temperature
Moisture content block
Inward Drive Experiment Setup
Sealed volume (2’/0.6 m square footprint), vapor
impermeable interior, airtight seal
T/RH and wafer sensors measure accumulation at
interior side (captures inward vapor drive)
Monitoring of Two Unvented Roofs with Air-Permeable Insulation in CZ 2A 47
© buildingscience.com
Inward Drive Experiment Results
RH and wafer sensor on interior interface has
seasonal variations, but not hitting 100% RH
Pattern correlates to 24-hour average of
sheathing temperature
Moisture adsorbing/desorbing from sheathing