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Conventional Roofing Assemblies: Measured Thermal Benefits of
Light to Dark Roofing Membranes and Alternate Insulation Strategies
Graham Finch MASc, P.Eng
RDH Building Engineering Ltd., Vancouver, BC – [email protected]
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Presentation Overview
• Conventional Roofing Designs and Current Issues
• Conventional Roofing Field Monitoring and Research Program
• Measured Insulation Performance • Selecting Roofing Membrane
Color and Insulation Strategy for Optimum Energy Efficiency
• Case Studies
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CONVENTIONAL ROOFING DESIGNS & CURRENT ISSUES
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Recap: Conventional Insulated Roofs • Most common low-slope roof application • Insulation installed above structure, protected by
roofing membrane – Insulation is typically foam plastic (polyiso, EPS), but also mineral fiber
• Roofing membranes are exposed to temperature, UV, traffic – needs to be durable
• Roof slope typically achieved by tapered insulation unless the structure is sloped
• Attachment of membrane/insulation can be: adhered, mechanically attached, loose laid ballasted, or combination of these
• Wood, concrete, or steel structure substrate • Air barrier and vapour control layer below insulation
on top of structure (depending on climate/design)
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Current Issues Seen in Conventional Insulated Roofs
• Roofing membrane issues – Two ply vs single ply systems, different membrane types – Details!
• Insulation movement – Thermally induced – Causes membrane ridging and stresses – Generally more movement with thicker amounts of insulation (becoming
more common) and certain insulations – More movement with darker colored membranes
• Insulation movement - Long term shrinkage, expansion, contraction – Gaps between insulation boards, induce membrane stresses
• Moisture trapped in insulation and roof assembly during wetting during construction or from small leaks in-service – Becoming more common to install leak detection monitoring within
conventional roofs and find this out – what to do about it? How to adjust monitoring?
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Membrane Ridging Due to Insulation Movement
TPO over gypsum board and polyiso
SBS over wood fiberboard and XPS
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Membrane Ridging Due to Insulation Movement
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Insulation Shrinkage
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Insulation Shrinkage Study • Polyiso has had a reported history of board shrinkage – both
initial and long-term – Related to manufacturer, mix, temperature, moisture, and age – Results in gaps between the insulation boards and induces stresses
introduced into roof membranes • Past monitoring shows varying amounts of ongoing shrinkage –
primarily influenced by age of product when installed
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Polyiso Shrinkage Monitoring Study
• Year 1 – 0.2% (2 mm in 1200 mm) Sh
rinka
ge -
mm
2010 2009
0
2
1
3 1/8”
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Polyiso Shrinkage Monitoring Study
• Year 4 – 0.2% to 0.7% (2-8 mm in 1200 mm)
Shrin
kage
- m
m
8
0
2
4
6
2009 2013
Year 1
1/4”
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Roof Membrane Color Considerations
• Roof membrane or ballast color (or more correctly solar absorptivity) influences surface temperature – Darker colors (more absorptive, less reflective)
results in higher temperatures, more assembly movement and membrane stress, higher cooling loads, lower heating loads
– Lighter colors (less absorptive, more reflective) results in lower temperatures, less assembly movement and membrane stress, lower cooling loads, higher heating loads
• Balance needed between membrane durability, assembly movement, heating and cooling loads
• Programs such as LEED have points for use of highly reflective roofs regardless of energy implication and local climate.
• Long term impacts and soiling of light colored roofs
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CONVENTIONAL ROOFING FIELD MONITORING STUDY
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Conventional Roofing Field Monitoring Study
• Why Monitor and Research? – Quantify performance of different colors of exposed roof
membrane (white, grey, black) – Quantify performance differences of stone wool, polyiso and
hybrid insulation combinations – Quantify combined impact of membrane color and insulation
strategy together – Observe impact of long term soiling of white SBS roofing – Monitor long-term shrinkage/movement of insulation and relative
humidity/moisture levels within insulation over tim
• While certain materials used for first phase of study – key findings are generally applicable to all membranes and insulation types
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Roof Membranes
• 3 different 2-ply SBS roof membrane cap sheet colors (white reflective, grey, black)
White Reflective Cap Sheet: SRI 70, Reflectance 0.58, Emittance 0.91 Grey Cap Sheet: SRI 9, Reflectance 0.14, Emittance 0.85 Black Cap Sheet: SRI -4, Reflectance 0.04, Emittance 0.85
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Insulation Assemblies • 3 different insulation strategies with same initial design R-value
Stone wool - R-21.4 (2.5” + 3.25”, adhered)
Polyiso - R-21.5 (2.0” + 1.5”, adhered)
Hybrid - R-21.3 (2.5” Stone wool + 2.0” Polyiso, adhered)
All insulation assemblies
approximately R-21.5 nominal.
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Insulation and Membrane Layout • 9 unique roof test areas, each 40’ x 40’ and independent • Similar indoor conditions and building use
Figure 1 Study Building and Layout of Roof Membrane Cap Sheet Color and Insulation Strategy
Polyiso
Hybrid
Stone wool
120’ 120’
Grey
White
Black
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Test Site – Vancouver Area, BC
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Sensor Installation • Temperature • Heat Flux • Relative Humidity &
Moisture Detection • Displacement • Solar Radiation
Heat Flux
Relative Humidity & Moisture Detection
Displacement
Temperature
Solar Radiation
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Sensor Positioning
T - Temperature RH - Relative Humidity HF - Heat Flux M - Displacement
M
M
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Visual Observations and Reflection Monitoring
• Visual indication to observe roof getting soiled over time • Solar Radiation & Reflected Radiation to observe change
over time of relative reflectivity
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Visual Observations and Reflection Monitoring
1 year after installation At installation
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Roof and Sensor Installation
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Roof and Sensor Installation
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Roof and Sensor Installation
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Roof and Sensor Installation
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MEASURED INSULATION PERFORMANCE
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My Most Common Designer Question Lately: What R-value is My Insulation?
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Laboratory Testing of Insulation R-values
• ASTM C518 thermal transmission material testing performed as part of monitoring study – Polyiso and stone wool insulation removed from site +
aged 4 year old polyiso samples from the previous monitoring study
– 3 different polyiso manufacturers tested (within first few months after manufacturing), density 3.0 to 3.4 pcf
– Wanted to know actual R-value as installed and temperature impacts to calibrate sensors
• Testing performed at mean insulation temperatures from 25, 40, 75, and 110°F to develop R-value vs temperature relationships
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Laboratory Testing of Project Polyiso and Stone Wool - R-value/inch
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
-‐10 0 10 20 30 40 50
R-‐value pe
r inch -‐IP un
its
Mean Temperature of Insulation -‐ oC
Installed & Aged Insulation R-‐values per Inch vs Mean Temperature
Polyiso -‐ New -‐ Average Polyiso -‐ New -‐ Minimum Polyiso -‐ New -‐ MaximumPolyiso -‐ Aged 4 yrs Stonewool -‐ Average
32°F 68°F 104°F
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Applying Our Laboratory Testing to the Field Assemblies
• Design/Code R-values for each assembly ~R-21.5
Stone Wool -2.5” + 3.25”, Weight 26.7 kg/m2, Heat Capacity – 22.7 kJ/K/m2
Polyiso - 2.0” + 1.5”, Weight 4.6 kg/m2, Heat Capacity – 6.8 kJ/K/m2
Hybrid – 2.5” Stone wool + 2.0” Polyiso, Weight 14.3 kg/m2, Heat Capacity – 13.7 kJ/K/m2
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Impact of Insulation Strategy and Roof Temperature on True R-value
14
15
16
17
18
19
20
21
22
23
24
-‐10 0 10 20 30 40 50 60 70 80
Appa
rent Roo
f Assembly R
-‐value
Outdoor Membrane Surface Temperature (Indoor, 21oC)
Apparent Roof Insulation R-‐value -‐ Based on Roof Membrane Temperature
Stonewool (Initial or Aged)Hybrid (Initial Average)Hybrid (Aged)Polyiso (Initial Average)Polyiso (Aged)
32°F 68°F 104°F 140°F
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FIELD MONITORING RESULTS
-‐25
-‐20
-‐15
-‐10
-‐5
0
5
10
Feb 21 Feb 22 Feb 23
Heat Flux [W
/m²]
Heat Flux Sensors
W-‐ISO HF
W-‐ISO-‐SW HF
W-‐SW HF
G-‐ISO HF
G-‐ISO-‐SW HF
G-‐SW HF
B-‐ISO HF
B-‐ISO-‐SW HF
B-‐SW HF
-‐25
-‐20
-‐15
-‐10
-‐5
0
5
10
Jun 30 Jul 1 Jul 2
Heat Flux [W
/m²]
Heat Flux Sensors
W-‐ISO HF
W-‐ISO-‐SW HF
W-‐SW HF
G-‐ISO HF
G-‐ISO-‐SW HF
G-‐SW HF
B-‐ISO HF
B-‐ISO-‐SW HF
B-‐SW HF
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Field Monitoring Results
• Monitoring from first 18 months shown today • Plan is to continue monitoring for 3+ years to look
at long-term trends and aging • Data shown for:
– Heat Flux – Temperature – Insulation Movement – Moisture
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Heat Flow – Heat Loss vs Heat Gain
-‐25
-‐20
-‐15
-‐10
-‐5
0
5
10
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Heat Flux [W
/m²]
Heat Flux Sensors
W-‐ISO HF
W-‐ISO-‐SW HF
W-‐SW HF
B-‐ISO HF
B-‐ISO-‐SW HF
B-‐SW HF
-‐25
-‐20
-‐15
-‐10
-‐5
0
5
10
Jun 30 0:00 Jun 30 6:00 Jun 30 12:00 Jun 30 18:00 Jul 1 0:00
Heat Flux [W
/m²]
Heat Flux Sensors
W-‐ISO HF
W-‐ISO-‐SW HF
W-‐SW HF
B-‐ISO HF
B-‐ISO-‐SW HF
B-‐SW HF
HeatLoss
Heat Gain
W- white, B-black, SW-stone wool, ISO - polyiso
1 W/m2 = 0.32 Btu/hr/ft2
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Heat Flow – Heat Loss vs Heat Gain
Winter vs. Summer
-‐25
-‐20
-‐15
-‐10
-‐5
0
5
10
Feb 21 Feb 22 Feb 23
Heat Flux [W
/m²]
Heat Flux Sensors
W-‐ISO HF
W-‐ISO-‐SW HF
W-‐SW HF
G-‐ISO HF
G-‐ISO-‐SW HF
G-‐SW HF
B-‐ISO HF
B-‐ISO-‐SW HF
B-‐SW HF-‐25
-‐20
-‐15
-‐10
-‐5
0
5
10
Jun 30 Jul 1 Jul 2
Heat Flux [W
/m²]
Heat Flux Sensors
W-‐ISO HF
W-‐ISO-‐SW HF
W-‐SW HF
G-‐ISO HF
G-‐ISO-‐SW HF
G-‐SW HF
B-‐ISO HF
B-‐ISO-‐SW HF
B-‐SW HF-‐25
-‐20
-‐15
-‐10
-‐5
0
5
10
Jun 30 Jul 1 Jul 2
Heat Flux [W
/m²]
Heat Flux Sensors
W-‐ISO HF
W-‐ISO-‐SW HF
W-‐SW HF
G-‐ISO HF
G-‐ISO-‐SW HF
G-‐SW HF
B-‐ISO HF
B-‐ISO-‐SW HF
B-‐SW HF
W- white, G-grey, B-black, SW-stone wool, ISO - polyiso
Heat Loss Heat Gain
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Net Seasonal Heat Flow & Direction
-‐250
-‐200
-‐150
-‐100
-‐50
0
50
100
W-‐ISO W-‐ISO-‐SW W-‐SW G-‐ISO G-‐ISO-‐SW G-‐SW B-‐ISO B-‐ISO-‐SW B-‐SW
Avg. Daily Ene
rgy Tran
sfer
[W·∙hr/m² p
er day]
Average Daily Energy Transfer During Different Exterior Conditions
Feb 21 to 23 Apr 22 to 24 May 9 to 11 June 30 to July 2
Outw
ardHeat Flow
Inward
Heat Flow
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Membrane & Deck Temperatures: Winter
16
18
20
22
24
26
28
Feb 22 0:00 Feb 22 6:00 Feb 22 12:00 Feb 22 18:00 Feb 23 0:00
Tempe
rature [°C]
Metal Deck Temperatures W-‐ISO TEMP-‐DECK
W-‐ISO-‐SW TEMP-‐DECK
W-‐SW TEMP-‐DECK
G-‐ISO TEMP-‐DECK
G-‐ISO-‐SW TEMP-‐DECK
G-‐SW TEMP-‐DECK
B-‐ISO TEMP-‐DECK
B-‐ISO-‐SW TEMP-‐DECK
B-‐SW TEMP-‐DECK
-‐2
0
2
4
6
8
10
12
Feb 22 0:00 Feb 22 6:00 Feb 22 12:00 Feb 22 18:00 Feb 23 0:00
Tempe
rature [°C]
Roof Membrane Cap Sheet Temperatures
W-‐ISO T-‐CAP
W-‐ISO-‐SW T-‐CAP
W-‐SW T-‐CAP
G-‐ISO T-‐CAP
G-‐ISO-‐SW T-‐CAP
G-‐SW T-‐CAP
B-‐ISO T-‐CAP
B-‐ISO-‐SW T-‐CAP
B-‐SW T-‐CAP
Outdoor-‐T
Roo
f Mem
bran
e M
etal
Dec
k
82°F
61°F
43°F
32°F
54°F
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Membrane & Deck Temperatures: Summer R
oof M
embr
ane
Met
al D
eck
0
10
20
30
40
50
60
70
80
90
Jun 30 0:00 Jun 30 6:00 Jun 30 12:00 Jun 30 18:00 Jul 1 0:00
Tempe
rature [°C]
Roof Membrane Cap Sheet Temperatures
W-‐ISO T-‐CAP
W-‐ISO-‐SW T-‐CAP
W-‐SW T-‐CAP
G-‐ISO T-‐CAP
G-‐ISO-‐SW T-‐CAP
G-‐SW T-‐CAP
B-‐ISO T-‐CAP
B-‐ISO-‐SW T-‐CAP
B-‐SW T-‐CAP
Outdoor-‐T
24
26
28
30
32
34
36
Jun 30 0:00 Jun 30 6:00 Jun 30 12:00 Jun 30 18:00 Jul 1 0:00
Tempe
rature [°C]
Metal Deck Temperatures W-‐ISO TEMP-‐DECK
W-‐ISO-‐SW TEMP-‐DECK
W-‐SW TEMP-‐DECK
G-‐ISO TEMP-‐DECK
G-‐ISO-‐SW TEMP-‐DECK
G-‐SW TEMP-‐DECK
B-‐ISO TEMP-‐DECK
B-‐ISO-‐SW TEMP-‐DECK
B-‐SW TEMP-‐DECK
176°F
140°F
104°F
68°F
97°F
75°F
86°F
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Roof and Insulation Movement to Date
-‐3.0
-‐2.0
-‐1.0
0.0
1.0
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Displacemen
t [mm]
Displacement -‐ Lower Insulation -‐ East-‐West
B-‐SW Lower W
W-‐SW Lower W
B-‐ISO Lower W
W-‐ISO Lower W
-‐3.0
-‐2.0
-‐1.0
0.0
1.0
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Displacemen
t [mm]
Displacement -‐ Upper Insulation -‐ East-‐West
B-‐SW Upper W W-‐SW Upper W B-‐ISO Upper W W-‐ISO Upper W
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0
10
20
30
40
50
60
70
80
90
100
Sep Oct NovDec Jan FebMar AprMay Jun Jul Aug Sep Oct NovDec Jan FebMar
Relativ
e Hu
midity
[%]
Relative Humidity Below Insulation
B-‐SW RH-‐B-‐INS
B-‐ISO-‐SW RH-‐B-‐INS
W-‐SW RH-‐B-‐INS
W-‐ISO-‐SW RH-‐B-‐INS
B-‐ISO RH-‐B-‐INS
W-‐ISO RH-‐B-‐INS
Relative Humidity Trends Below Insulation
All roofs constructed under dry summer conditions, no rain – dry to start
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Jun 30 00:00 Jun 30 12:00 Jul 01 00:00 Jul 01 12:00 Jul 02 00:00
Relativ
e Hu
midity
[%]
Relative Humidity Below Insulation
B-‐SW RH-‐B-‐INS
B-‐ISO-‐SW RH-‐B-‐INS
W-‐SW RH-‐B-‐INS
W-‐ISO-‐SW RH-‐B-‐INS
B-‐ISO RH-‐B-‐INS
W-‐ISO RH-‐B-‐INS
Relative Humidity Trends Below Insulation
All roofs constructed under dry summer conditions, no rain – dry to start
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Relative Humidity Impact on Roof?
September 26, 2013 – Clear and Cool at 7 am – air temperature 4°C/39°F
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Other Site Observations
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OPTIMIZING MEMBRANE COLOR AND INSULATION STRATEGY FOR ENERGY EFFICIENCY
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Energy Consumption and Membrane/Insulation Design
• Calibrated energy modeling used to compare roof membrane color/solar absorptivity & insulation strategy – White, Grey or Black Roof Membrane – Polyiso, Stone wool, or Hybrid insulation approach
• Stone wool has lower R-value/inch but higher heat capacity and higher mass
• Polyiso has a higher R-value/inch (varies with temperature) and has a lower heat capacity and lower mass
• Hybrid approach has stone wool over top of polyiso which moderates temperature extremes of polyiso insulation – makes polyiso perform better
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Energy Consumption and Membrane/Insulation Design
• Energy modeling performed for a commercial retail building (ASHRAE commercial building prototype template)
• Results calibrated with temperature/heat-flux data from monitoring study
• Input temperature dependant & aged R-values into energy model – base R-20 roofs
• Help to select the optimum insulation and membrane color combination for energy efficiency
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Energy Modeling of Temperature Dependant Insulation R-values
• Input our temperature dependant insulation R-value for polyiso and stone wool into EnergyPlus
– Heating energy for Climate Zone 4 (Vancouver) shown here, R-20 insulation – Impact is significant enough that should be accounted for – Results in different design rankings of lowest to highest energy consumption
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Dark Roof Gray Roof White Roof
Annu
al Heatin
g En
ergy Con
sumption,
kWh/m
2
Model Default -‐ Constant Conductivity
Polyiso
Stone wool
Hybrid
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Dark Roof Gray Roof White Roof
Annu
al Heatin
g En
ergy Con
sumption,
kWh/m
2
Revised Model -‐ Temperature Dependent Conductivity
Polyiso
Stone Wool
Hybrid
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Most Energy Efficient Roofing Combination in Study Building Climate?
Heating Energy Cooling Energy Total Energy
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Most Energy Efficient – By Climate?
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1 -‐ Miami 2 -‐ Houston 3 -‐ San Francisco 4 -‐ Baltimore 5 -‐ Vancouver 6 -‐ Burlington VT 7 -‐ Duluth 8 -‐ Fairbanks
Annu
al Heatin
g En
ergy, kWh/m
2
Climate Zone
Black -‐ Aged Polyiso
Black -‐ Stonewool
Black -‐ Aged Hybrid
White -‐ Aged Polyiso
White -‐ Stonewool
White -‐ Aged Hybrid
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1 -‐ Miami 2 -‐ Houston 3 -‐ San Francisco 4 -‐ Baltimore 5 -‐ Vancouver 6 -‐ Burlington VT 7 -‐ Duluth 8 -‐ Fairbanks
Annu
al Coo
ling En
ergy, kWh/m
2
Climate Zone
Black -‐ Aged Polyiso
Black -‐ Stonewool
Black -‐ Aged Hybrid
White -‐ Aged Polyiso
White -‐ Stonewool
White -‐ Aged Hybrid
Commercial Retail Building Heating Energy – kWh/m2/yr
Commercial Retail Building Cooling Energy – kWh/m2/yr
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Most Energy Efficient Combination?
Lighter membrane, stone wool or hybrid is better for same design R-value
Darker membrane, stone wool or hybrid is better for same design R-value
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CASE STUDIES: STONE WOOL & HYBRID COMBINATIONS IN CONVENTIONAL ROOFING
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Stone Wool Insulation in Conventional Roofing
• R-value of stone wool is R-3.7/inch compared to a R-4 to R-6/inch for polyiso or R-4/inch for EPS – Need thicker stone wool to achieve same
R-value as polyiso in design
• If polyiso kept closer to indoor temperatures, then it has a higher effective R/inch (closer to LTTR) – Insulate the Polyiso!
• Hybrid insulation provides good blend of material properties and economics
• Tapered insulation packages available: EPS, Polyiso, or Stone wool
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Case Study 1
• 2-ply SBS torched to 2” stone wool over 2” Polyiso (adhered)
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Case Study 2
• 2-ply SBS torched to 2” stone wool over 2” Polyiso over tapered polyiso (mechanically attached)
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Case Study 3
Who forgot to lap?
• 2-ply SBS torched to 2” stone wool over tapered polyiso (adhered)
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Case Study 4
• 2-ply SBS torched to 1” stone wool with asphalt facer adhered to 2” stone wool adhered to EPS taper package, mechanically fastened
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Designer and Roofing Contractor Feedback to Date on Systems
• Stone wool insulation easy and fast to install. • Stone wool insulation lays flat and takes up uneven surfaces, tight
board installation, very few gaps compared to polyiso. • Stone wool is softer than polyiso and potentially softens during
construction from foot traffic – not issue in open field areas, but compression can occur in high traffic areas prior to covering – can address with extra asphalt protection board overlay.
• Thicker insulation build-up for stone wool compared to polyiso due to R-value differences, may be an issue where roof height is at a premium or could be issue during re-roof around existing doors and curbs etc.
• Careful with mechanical fasteners without a protection board. • Adhesive with stone wool must be applied and set-in quickly before
foam expands. Slightly different process than with polyiso.
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Recommended Conventional Roofing Strategies for Energy & Durability
• Design to provide good balance of cost, thickness, & performance (energy, durability, membrane life)
• Roof Membrane – grey or other neutral color for northern climates, light in south
• Adhered system with stone wool insulation as top layer (30-50% of total insulation R-value)
• Layer of polyiso below with taper package (EPS)
• Self adhered/torched sheet air/vapour barrier membrane (temporary roof) over substrate
• Adhered layers preferred instead of mechanically attached, where possible to balance cost
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Summary – Key Points
• Research and Field Monitoring Study Findings – Design R-value may change in service – all types of
insulation are affected to varying degrees – Is not Static – In addition to design R-value - heat capacity and latent
moisture transfer within insulation has an impact on temperatures and energy transfer
– Movement of insulation less than anticipated so far – Entrapped moisture will ping-pong around more in
stonewool than polyiso – RH fluctuations normal – Optimization of heating and cooling based on roof
membrane color and insulation strategy suggested – Careful selection of insulation strategy and membrane colour
will have a positive impact on roof assembly performance