The
Benefits of EPS Roof Insulation
by W. James Whalen, P. Eng
Construction Canada Magazine - January 2004, Vol. 46, No. 1
Moulded expanded polystyrene
(EPS) insulation is widely used as the insulation component in low-slope
commercial and industrial roof assemblies in order to reduce energy loss.
The main criterion for selecting the thickness of EPS insulation typically
is a cost/benefit analysis designed to balance the capital cost of the
insulation against the saving in energy costs over the life of the building.
However, there are many other performance criteria that must be reviewed
during the design process in order to ensure the ideal EPS insulation
type is selected for application.
The material properties for the three standard EPS insulation types in
the National Standard of Canada for EPS insulation, CAN/ULC-S701-01(1),
are shown in Table 1.
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The design parameters
required for the insulation component in roof assemblies have been identified
in a number of publications. In particular, the desirable properties of
roof insulation were reviewed in a 1999 article(2) by Mark S. Graham, associate executive director of technical services
for the National Roofing Contractors Association (NRCA). That article
provides a comparison of material properties for different types of rigid
insulation, but emphasizes that test methods used to determine material
property values are not always the same for different types of rigid insulation.
The NRCA roofing and waterproofing manual(3) provides
the desirable properties identified in the Graham article. Ideal rigid
insulation would have the following properties:
1. Bitumen and adhesive compatibility-The ability to withstand the effects
of adhesives, solvents and hot bitumen at the application temperatures
required for installation of a roof membrane.
2. Impact resistance-High enough strength, rigidity and density to resist
impact damage.
3. Fire resistance-Incombustibility and compliance with insurance underwriter
and building code requirements.
4. Durability-Constructed of materials that resist rot and deterioration.
5. Moisture resistance-Resistant to the effects of moisture vapour and
free water.
6. Thermal resistance-The highest possible thermal resistance (R-value)
so the thinnest piece of material of a particular type of insulation can
be used.
7. Stable R-Value-Constant thermal resistance that does not drift with
age (i.e. the insulation will not lose thermal resistance over time).
8. Attachment capability-A surface that accommodates secure attachment.
9. Dimensional stability-The ability to remain dimensionally stable under
varying temperature and moisture conditions.
10. Component compatibility-Formulated to be compatible with other roof
assembly components.
The NRCA recognizes that no single commercial insulation can provide all
of the 10 properties identified above. As well, it is recognized that
appropriate test methods for determination of acceptable product performance
based upon these properties are not always available. The performance
characteristics of EPS insulation in relation to the above criteria are
as follows.
Compatibility with
bitumen and other adhesives
Hot asphalt is frequently used in roof assemblies to adhere EPS insulation
to wood fibreboard or gypsum board serving as either the thermal barrier
or protection board in the roof assembly. In these types of applications,
hot asphalt is applied to the wood fibreboard or gypsum board at a specific
application rate-e.g. 1 kg/sq. m (20 lb/square)-then allowed to cool to
93-121 C (225-250 F) before applying to the EPS insulation.
In the application of any adhesive to a substrate, the adhesive must penetrate
and adhere to the base layer sufficiently to establish bond without degradation
of the bonded insulation. In the case of hot asphalt applied to EPS insulation,
the asphalt temperature and the application rate will dictate the success
of the EPS insulation bond, as well as any degradation of the bonded insulation.
Various types of water-based, solvent-free, rubberized asphalt emulsion
adhesives are also available for use with EPS insulation. These types
of adhesives offer the advantages of low temperature flexibility, non-combustibility
and water resistance when cured. They provide excellent bond strength
for use in bonding EPS insulation to EPS insulation, laminating cover
boards to EPS insulation or attaching EPS insulation to substrates.
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| EPS
insulation is used in a single-ply, loose-laid ballasted system in
an industrial roof project. |
Impact resistance
The mechanical properties of EPS insulation offer a combination of compressive
resistance and flexibility to resist impact loads. The three standard
EPS insulation types available on the market offer a range of compressive
resistance sufficient to support typical roof loads.
When used in roofing applications, the insulation must withstand installation
traffic, support fastener loads and the total roofing system. The designer
of the building must determine the specific compressive resistance values
needed for a roof application based on a review of these criteria.
Foam plastic insulation standards provide compressive resistance based
upon loads measured at 10 per cent deformation from original thickness
or yield, whichever occurs first. However, when compressive resistance
is considered as a design property for foam plastic insulation, it must
be recognized that long-term compressive load should not exceed the elastic
limit of the product.
Roof loads during construction may be the most rigorous test of the insulation
material. In October 1989, the National Roofing Contractors Association
(NRCA) issued a report that reviewed the performance of phenolic and polyisocyanurate
insulations under simulated field conditions(4).
The report indicated significant damage to the insulation material could
occur during roof construction. Since EPS insulation is commonly used
in roofing applications and it was excluded from this report, additional
testing was undertaken by Plasti-Fab Ltd. to develop test results under
comparable conditions for EPS insulation.
The Plasti-Fab report(5) summarized testing completed
in June 1993 for phenolic, polyisocyanurate and EPS insulation products
subjected to the same test procedure. As with the NRCA test program, the
test procedure used simulated traffic over roof insulation during installation
of a ballasted loose-laid EPDM roofing system. Each insulation type was
tested using five, 10 and 20 passes of a ballast buggy, with and without
ballast in place.
Deformation is considered unacceptable if it is permanent or, in other
words, the material does not spring back or recover original thickness
when the load is removed. Compressed insulation cells typically reduce
the insulation value of the material in the compressed area. Unlike many
rigid insulation materials, EPS insulation provides good elasticity or
resiliency when compressive loads are applied. The damage to EPS insulation
samples in this test program after five, 10 and 20 passes of the ballast
buggy was restricted to tracking on the insulation surface-i.e. minor
compression of the top surface of the EPS insulation along the path of
the ballast buggy wheels.
Fire resistance
Foam plastic insulations such as EPS insulation are permitted in roof
assemblies that form part of either combustible or non-combustible construction.
For example, Article 3.1.14.2.1 of the National Building Code (NBC) of
Canada addresses the use of EPS insulation in metal roof deck assemblies
that form part of buildings required to be of non-combustible construction.
NBC Sentence 3.1.14.2.1(1) indicates manufacturers must demonstrate that
the insulation component in a metal roof assembly has been tested as a
component in a roof assembly complying with the conditions of acceptance
in CAN/ULC-S126-M(6). The requirement to demonstrate
compliance with CAN/ULC-S126-M is waived if any of the following requirements
included in NBC Sentence 3.1.14.2.(2) are met for the roof assembly:
(a) A 12.7-mm (1/2-in.) gypsum board or other thermal barrier meeting
the requirements of CAN/ULC-S124-M is located on the underside of the
foam plastic insulation.
(b) The building is sprinklered throughout.
(c) The roof assembly has a fire-resistance rating of not less than 45
minutes.
If any of the requirements in NBC Sentence 3.1.14.2.(2) are met (e.g.
building is sprinklered throughout), EPS insulation may be applied directly
to the roof metal deck.
EPS insulation is included as an accepted component in a number of CAN/ULC-S126
listed roof assemblies. As well, EPS insulation is included in a number
of Factory Mutual Global listed roof assemblies.
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| EPS
Insulation installedin direct-to-deck single-ply loose-laid ballasted
system. |
Durability
EPS insulation is inert to a wide range of chemicals. It has no food value,
will not rot or decay and does not provide any nutrient value for insects,
parasites or animal and plant life. As well, EPS insulation is able to
withstand temperature cycling, assuring long-term performance. In a series
of tests conducted by Dynatech Research and Development Co.,(7) test results for EPS insulation core specimens removed from freezer walls,
some as old as 16 years, confirmed that EPS withstands freeze-thaw cycling
without loss of structural integrity or other material properties.
Moisture resistance
The closed cell structure of EPS insulation provides excellent resistance
to moisture absorption. A study by the Energy Materials Testing Lab (EMTL)(8) that exposed EPS insulation to simulated extreme winter conditions demonstrated
EPS insulation installed in well-constructed roofs would not absorb appreciable
moisture. The study found EPS insulation picked up small amount of moisture,
in the order of 0.2 per cent by weight, even under conditions characteristic
of prolonged, cold, damp winters.
Water vapour transmission is the passage of water through a material in
the vapour phase. Each roof assembly design should be studied to determine
the need for a vapour barrier to control internal condensation. In comparison
to other common building materials, EPS insulation has moderate water
vapour permeability per unit of thickness. The water vapour permeance
characteristics of EPS insulation will vary with thickness (see Table
1, note 2). Where water vapour permeance is a design issue, the EPS insulation
manufacturer should be consulted for additional information.
Thermal resistance
value
The closed cell structure of EPS insulation does not contain a captive
blowing agent, such as HCFC. EPS insulation is the only rigid foam plastic
insulation not subject to decrease in thermal resistance value as it ages-i.e.
thermal drift-as a result of loss of captive blowing agent. In this respect,
there is an important distinction to be made between EPS insulation and
other rigid foam plastic insulation products whose thermal resistance
value changes as the effectiveness of the low thermal conductivity blowing
agent introduced into the cellular structure during manufacture decreases.
As requirements for elimination of HCFC blowing agent are adopted by other
foam plastic insulation manufacturers, their raw materials and manufacturing
processes will need to be adjusted. The raw materials used in the manufacture
of EPS insulation have remained consistent over its more than 40-year
history with constant improvements in the manufacturing process, including
the introduction of vacuum mould technology.
Stable thermal
resistance value
EPS insulation was used as the reference material in the National Research
Council (NRC) of Canada research program to develop a test procedure for
predicting long-term thermal performance of board stock foam insulation
containing a captive blowing agent. As the closed cell structure of EPS
insulation contains only air, the R-value is not subject to thermal drift
(decrease) as the insulation ages.
The thermal performance of EPS insulation was reviewed in a supplementary
report issued by the NRC(9). Based on continuous
monitoring over a two-year period in a field condition simulating a roof
application and periodic laboratory measurement of the thermal resistance
for reference specimens, the thermal resistance of EPS insulation was
found to be very stable. The average thermal resistance remained constant
over the two-year monitoring period.
Attachment capability
The design of a roof assembly must include provision for proper restraint
of the insulation and other assembly components in relation to:
1. The physical properties of all components within the roof assembly.
2. The effect of attachment method on the insulation components.
3. The composite properties of the individual system components.
A review of EPS insulation response to various attachment methods was
conducted under a two-year test program.(10) The
review, conducted as part of a joint research program involving the EPS
insulation industry and U.S. roofing contractors' associations, confirmed
that mechanical fasteners or hot asphalt can be used as effective attachment
methods for roof assemblies containing EPS insulation.
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| This
university building uses EPS insulation board for roof insulation. |
Dimensional stability
Dimensional stability in roofing assemblies is a measure of the degree
to which a material maintains its original dimensions when subjected to
changes in temperature and humidity. The dimensional stability value for
EPS insulation in CAN/ULC-S701 (maximum 1.5 per cent linear change) provides
an indication of maximum allowable linear dimensional change when the
insulation is subjected to an elevated temperature of 70±2 C (158±2
F) for a period of seven days. The CAN/ULC-S701 value is a maximum allowable
value; however, actual values from testing of EPS insulation are typically
much lower.
The test procedure for determining dimensional stability provides an indication
of maximum irreversible change in dimension when a product is subjected
to a full thickness temperature change for an extended period of time.
The applicability of these values to typical roof insulation applications
where a thermal gradient exists is limited. As a general rule, if the
EPS insulation is attached to a substrate, the thermal expansion or contraction
of the roof assembly will depend on the expansion or contraction of the
other components within the assembly.
Component compatibility
EPS insulation is compatible with common roof assembly components, including
built-up roof and single-ply roof membranes. As noted previously, EPS
insulation can be used in roof assemblies for buildings required to be
of either combustible or non-combustible construction.
Conclusion
A designer must select an insulation material with the best combination
of the desired properties based upon empirical test data and knowledge
of past performance. As recognized by the NRCA, no insulation material
will provide all of the desired material properties. However, moulded
EPS insulation provides a range of material properties that makes it suitable
for a wide variety of roofing applications.
The most notable characteristic of EPS insulation in comparison to other
foam plastic insulation is its stable thermal resistance value. Other
types of foam plastic insulations are manufactured with the intent to
retain a blowing agent other than air for a period of longer than 180
days. A specific test method(11) has been developed
to provide a means for predicting the long-term thermal resistance (LTTR)
based on an accelerated laboratory test, because it is recognized that
the thermal resistance of these types of foam plastic insulation will
decrease with time. However, EPS insulation does not contain a captive
blowing agent, so it is not affected by the LTTR requirement.
The range of EPS insulation types in CAN/ULC-S701 offers versatility in
meeting project-specific applications. The material property values in
CAN/ULC-S701 provide a means of comparing different types of cellular
plastic thermal insulation and are intended for use in specifications,
product evaluations and quality control. However, it must be noted that
the test methods used to determine these material properties do not always
predict end-use product performance. The choice of the appropriate type
of EPS insulation board will require a review of the above performance
criteria for the specific roofing system being considered.
W. James Whalen,
P.Eng., is technical marketing manager at Plasti-Fab. Ltd. in Calgary,
Alta. He can be reached at (403) 569-4312 or jwhalen@plastifab.com.
References
1 CAN/ULC-S701-01, Standard for Thermal Insulation, Polystyrene, Boards
and Pipe Covering, published by Underwriters' Laboratories of Canada.
2 Properties of Rigid Roof Insulation, Technology Today, Professional
Roofing magazine, May 1999, published by the National Roofing Contractors
Association.
3 The Roofing and Waterproofing Manual, Third Edition, 1989, published
by the National Roofing Contractors Association.
4 Result of Crushing, Membrane Adhesion and Uplift Tests on Phenolic and
Polyisocyanurate Foam Insulations, October, 1989, report prepared jointly
by members of the Midwest Roofing Contractors Association and the National
Roofing Contractors Association.
5 Report on Crushing Test Results for Moulded Expanded Polystyrene, Phenolic
and Polyisocyanurate Foam Insulations, June 1993, report prepared by Plasti-Fab
Ltd.
6 CAN/ULC-S126-M, Standard Method of Test for Fire Spread Under Roof-Deck
Assemblies, published by Underwriters' Laboratories of Canada.
7 The Apparent Thermal Conductivity and Thermal Resistance of an Expanded
Polystyrene Foam Specimen Removed From a Refrigerated Warehouse, Andre
O. Desjarlais, Dynatech Research and Development, March 1979.
8 Development of Experimental Data on Expanded Polystyrene Roofing Insulation
Under Simulated Winter Exposure Conditions, R.P. Tye and C.F. Baker, The
Energy Materials Testing Laboratory, 1984.
9 Procedures to Predict Long-Term Thermal Performance of Boardstock Foam
Insulations, Mark Bomberg and Mavinkal Kumaran, National Research Council
of Canada, 1995.
10 Application of EPS Insulation for Optimum Performance in BUR and Single-Ply
Roofing Systems, David. L. Johnston, Arco Chemical Co., Seventh Conference
on Roofing Technology, 1983.
11 CAN/ULC-S770-00, Standard Test Method for Determination of Long-Term
Thermal Resistance of Closed-Cell Thermal Insulating Foams, published
by Underwriters' Laboratories of Canada.
Reprinted
with permission of Construction Specifications Canada, 120 Carlton St.,
Suite 312, Toronto, ON M5A 4K2, from Construction Canada.
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