Conventional Roofs: Measuring Impacts of Insulation Strategy and Membrane Colour in Canada LORNE RICKETTS, MASC RDH BUILDING ENGINEERING LTD. VANCOUVER, BC CO-AUTHORS: GRAHAM FINCH, MASC, P.ENG. & MARCUS DELL, MASC P.ENG.
NBEC 2014 - Conventional Roofs: Measuring Impacts of Insulation Strategy and Membrane Colour in Canada
Jul 15, 2015
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Conventional Roofs: Measuring Impacts of Insulation Strategy and Membrane Colour in Canada LORNE RICKETTS, MASC
RDH BUILDING ENGINEERING LTD. VANCOUVER, BC
CO-AUTHORS: GRAHAM FINCH, MASC, P.ENG. & MARCUS DELL, MASC P.ENG.
Outline
à Introduction & Background à What prompted the study?
à Study of Conventional Roof Performance à Laboratory Testing
à Field Monitoring
à Energy Modelling
à Conclusions & Areas of Continuing Research
Conventional Roofing Recap
à Most common low-slope roof in North America
à Air barrier and vapour control layer below
insulation on top of structure, then insulation,
then membrane on top
à Insulation typically foam plastic (polyiso, EPS),
mineral fibre also used
à Roof slope typically achieved by tapered
insulation unless structure is sloped
à Roof membrane exposed to temperature, UV,
traffic – needs to be durable
à Attachment of membrane/insulation can be
adhered, mechanically attached, loose laid
ballasted, or combination
Polyiso Shrinkage
Ridged Membrane
Insulation Issues
à Long-term shrinkage
à Thermal expansion/contraction
What Prompted the Study?
XPS Expansion
EPS Shrinkage
What Prompted the Study?
Cover Board Issues
à Delamination & fungal growth
Wood fiberboard cover-board wetting and delamination
Wetting & resulting fungal growth on gypsum cover board
What Prompted the Study
The Great Colo(u)r Debate à Darker Colours (more absorptive, less reflective)
à Higher temperatures, more movement and
membrane stress, higher cooling loads, lower
heating loads
à Lighter Colours (less absorptive, more reflective)
à Lower temperatures, less movement and
membrane stress, lower cooling loads, higher
heating loads
à LEED points for use of highly
reflective roofs regardless of energy
implication and local climate
à Balance needed between membrane
durability, assembly movement,
heating and cooling loads
Confused owner?
New 5 Years Old
Study of Conventional Roof Performance
Guiding Purpose of the Study – Why?
à Quantify performance of different colours of exposed roof membrane
à White, Grey, & Black
à Quantify performance of different insulation types
à Stone wool, Polyiso, & Hybrid
à Quantify combined impact of membrane colour and insulation
à Observe impact of the long-term soiling of white SBS cap sheets
à Monitor long-term shrinkage/movement of insulation and relative
humidity/moisture levels within insulation
à Laboratory testing of material properties
Roof Membrane Colours
à 3 different 2-ply SBS roof
membrane cap sheet colours
(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
3 Different Insulation Strategies
Stone wool - R-21.4 (2.5” + 3.25”, adhered)
Weight: 26.7 kg/m2 Heat Capacity: 22.7 kJ/K/m2
Polyiso - R-21.5 (2.0” + 1.5”, adhered)
Weight: 4.6 kg/m2 Heat Capacity: 6.8 kJ/K/m2
Hybrid - R-21.3 (2.5” Stone wool + 2.0” Polyiso, adhered)
Weight 14.3 kg/m2, Heat Capacity – 13.7 kJ/K/m2
Design target: Each Assembly the same ~R-21.5 nominal
Insulation and Cap Sheet Layout
à 9 unique roof test areas, each 40’ x 40’ and each behaving
independently
à Similar indoor conditions (room temperature) and building use
(warehouse storage)
à Climate Zone 4
Figure 1 Study Building and Layout of Roof Membrane Cap Sheet Color and Insulation Strategy
Polyiso
Hybrid
Stone wool
120’ 120’
Grey
White
Black
Polyiso Hybrid
Stonewool
Sensor Selection and Installation
à Temperature
à Heat Flux
à Relative Humidity
à Moisture Detection
à Displacement
à Solar Radiation
Heat Flux
Relative Humidity & Moisture Detection
Displacement
Temperature
Solar Radiation
Laboratory Testing of Insulation Performance
Laboratory Testing of Insulation R-values
à 3rd Party ASTM C518 thermal
transmission material testing
à Polyiso and stone wool insulation removed from site & 4 year old polyiso samples from prior study
Laboratory Testing of Project Insulation
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
Mean Temperature of Insulation [°C]
Installed & Aged Insulation R-‐values -‐ Based on Mean Temperature
Polyiso -‐ Maximum Polyiso -‐ Average Polyiso -‐ Minimum
Polyiso -‐ Aged (4 years) Stone Wool -‐ Average
14
15
16
17
18
19
20
21
22
23
24
-‐10 0 10 20 30 40 50 60
Effective Assembly R-‐value
Outdoor Membrane Surface Temperature (Indoor, 21oC)
Effective Roof Insulation R-‐value -‐ Based on Roof Membrane Temperature
Stone Wool (Initial or Aged)
Hybrid (Initial Average)
Hybrid (Aged)
Polyiso (Initial Average)
Polyiso (Aged)
Varying R-value of Field Roof Assemblies
Field Monitoring Findings
Study Findings: What is the Impact of Membrane Colour?
32
50
68
86
104
122
140
158
176
194
0
10
20
30
40
50
60
70
80
90
May Jun Jul Aug Sept Oct Nov Dec Jan Feb Mar Apr
Tempe
rature [°F]
Tempe
rature [°C]
Monthly Average of Daily Maximum Membrane Temperatures and Maximum Membrane Temperature for Each Month by Membrane Colour
White Grey Black White -‐ Maximum Grey -‐ Maximum Black -‐ Maximum
* *
*W-‐ISO-‐SW had significant data loss in August and September and is removed from the average for those months.
Colour – Impact on Surface Temperatures
à Increased temperatures affect:
à Membrane degradation/durability
à Heat/Energy Flow through assembly
Study Findings: What is the impact of insulation arrangement?
Insulation Impact on Peak & Lagging Membrane & Metal Deck Temperatures
Ro
of
Mem
bra
ne
Meta
l D
eck
Heat Flow – Variation with Insulation Strategy
SENSOR CODING: SW - stone wool, ISO – polyiso, ISO-SW - hybrid
-‐25
-‐20
-‐15
-‐10
-‐5
0
5
10
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Heat Flux [W
/m²]
Heat Flux Sensors
G-‐ISO HF
G-‐ISO-‐SW HF
G-‐SW HF
Net Annual Impact of Insulation Strategy
0
100
200
300
400
500
600
-‐150
-‐100
-‐50
0
50
100
May Jun Jul Aug Sept Oct Nov Dec Jan Feb Mar Apr Annual
Degree
Days [°C·∙da
ys]
Daily Ene
rgy Tran
sfer [W
·∙hr/m² p
er day]
Monthly Average Daily Energy Transfer by Insulation Arrangement
ISO ISO-‐SW SW Heating Degree Days (18°C)
OutwardHe
at Flow
InwardHe
at Flow
1 W/m2 = 0.32 Btu/hr·ft2
Ou
tward
H
eat
Flo
w
Inw
ard
H
eat
Flo
w
Other Findings to Date
à Insulation Movement monitoring ongoing
à Observing daily insulation swings
à Seeing some long-term movement of
insulation, but also movement of metal deck
structure interfering with long-term data
à Relative Humidity and moisture movement
ongoing
à Seeing harmless seasonal and daily
movement of built-in water vapor
à Water vapor also moves energy – latent heat
à Cut-tests confirm roofs all dry and no issues
Impact of Membrane Colour and Insulation Strategy on Energy Consumption
Energy Consumption and Membrane/ Insulation Design
à Energy modeling performed for a commercial retail building (ASHRAE
building prototype template) to compare
roof membrane colour & insulation strategy
à Included more realistic thermal performance of
insulation into energy models
à Stone wool: Lower R-value/inch
Higher heat capacity and mass
à Polyiso: Higher R-value/inch
(varies with temperature a lot)
Lower heat capacity
Lower mass à Hybrid: Moderates temperature extremes
of polyiso – makes polyiso
perform better
Most Energy Efficient Roofing 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
Conclusions & Continuing Research
à Aging and temperature have significant effects on the thermal performance
of insulation – all types affected to varying degrees
à Effective insulation R-values, thermal mass, latent heat transfer, membrane
colo(u)r all impact membrane temperatures and heat flows
à Effects building energy consumption and membrane durability
Rated R-values of insulation do not tell the whole
story about actual heat flow through roofs.
à 2 years so far, but study is ongoing
à Soiling, long-term movements, aging etc.
à Confirm impacts of moisture movement within the assemblies
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