UPDATED on January 25, with information on phenolic foam.
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Maybe you&#;ve decided that your floor, wall, or roof assembly needs one or more layers of rigid foam. Which type of foam should you choose: polyisocyanurate, expanded polystyrene (EPS), or extruded polystyrene (XPS)?
The answer depends on several factors, including your R-value target, your local climate, whether the insulation will be in contact with soil, and your level of environmental concern.
Manufacturers of insulation products are required to provide consumers with R-value information. If you&#;ve purchased rigid foam insulation that isn&#;t clearly labeled, contact the manufacturer to learn the product&#;s R-value.
Over a period of decades, the R-value of polyisocyanurate and XPS gradually declines. For more information on this phenomenon, called &#;thermal drift,&#; see Thermal Drift of Polyiso and XPS.
Rigid foam manufacturers are required to perform R-value tests using an ASTM method specifying that the test be performed at a mean temperature of 75°F. At lower mean temperatures, EPS and XPS perform better than their R-value label indicates. In other words, as the temperature drops, the ability of EPS and XPS to resist heat flow improves.
Polyiso behaves differently: as the mean temperature drops, it does a worse job of resisting heat flow. For that reason, some cold-climate builders assign a lower R-value for polyiso &#; perhaps R-4.5 or R-5 per inch &#; than the R-value on the&#;
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Choosing the right insulation for an application can be complicated due to varying product types, thicknesses and long-term performance ratings. That&#;s why the ASTM C578 international standard was developed. This guide lists the various physical properties of both expanded polystyrene (EPS) rigid foam insulation and extruded polystyrene (XPS) rigid foam insulation. Contractors can use these standards to ensure they are not only picking an adequate insulation product for roofing and wall insulation but also one that will perform as needed throughout its service life. To use these standards properly, however, it is important for contractors to know how they work and how to apply them in different applications.
ASTM C578 classifies several types of EPS foam products: Type I, Type VIII, Type II, Type IX, Type XIV and Type XV. Each classification designates the product&#;s physical properties, such as density, compressive strength, flexural strength, thermal resistance, water vapor permeance and water absorption. Contractors looking to these standards can quickly confirm how a product will perform when used, which can take some of the uncertainty out of choosing the right insulation for a project.
Further, with such definite classifications, industry organizations can easily make recommendations for specific applications. For example, the National Roofing Contractors Association (NRCA) can recommend roofing insulation that uses EPS foam be, at minimum, Type VIII. This means contractors can know exactly which type of insulation to use without having to consult multiple documents and standards.
Because ASTM C578 is an international classification standard, most EPS foam types fit one of the categories listed within the standard. As such, contractors can buy ASTM C578 EPS foam anywhere EPS foam is sold. They should make sure that the product is labeled and as C578 compliant and that a third-party certification agency is part of the quality control process. They should also be aware of what type of insulation (and its physical properties) to ensure they buy the correct insulation for their project.
Contractors looking for roof or wall insulation that meets their application needs should instead use the ASTM C578 standards as a guide. In addition, it is highly recommended to consult with relevant associations for best practice recommendations.
Contractors wanting to increase the insulation rating of a project&#;s walls should first consult Energy Star&#;s R-value recommendations by region. Once they know what minimum values they need, they can consult the ASTM C578 standards to see which type of EPS foam can most efficiently meet the insulation needs of their project. In this way, ASTM C578 can help contractors find the most effective way to insulate a wall.
While contractors can certainly choose other insulation types to achieve an adequate R-value, it should be noted that many insulation types can lose their R-values over time due to damage, moisture and settling. This means insulation that meets recommended R-values today may not in the future, reducing energy efficiency and occupant comfort. EPS foam, on the other hand, has a stable R-value. Its ability to insulate will remain consistent from the day it&#;s installed to the day it&#;s replaced.
Likewise, when shoring up roofing insulation, contractors can use ASTM C578 as a guide to identify which insulations will efficiently meet R-value goals. Not only can lightweight EPS foam meet the R-value requirements of many regions, but it is also easy to install. Contractors and homeowners alike no longer have to deal with fiberglass splinters from difficult-to-cut batts or complicated machinery for blown-in insulation. EPS foam panels can be cut to size and installed with standard tools. This, in combination with its stable R-value, makes EPS foam an ideal material for adding or upgrading roof insulation.
Most construction standards can be challenging to parse and are required. ASTM C578 is different. This international standard creates a classification system so contractors can easily reference which types of insulation will fit their needs.
Like any tool, it can be used properly and improperly. When contractors consult the ASTM C578 standards in conjunction with recommendations from industry associations, they can rest assured they are choosing the right insulation type for their projects. And when they use EPS foam to meet their insulation goals, they can know that it will be easy to install and retain its R-value year after year.
For more information about EPS foam&#;s qualities, check out this comparison chart.
If you want to learn more, please visit our website Extruded Foam Insulation.