06/01/2009

Insulation: EPS and XPS

There are two insulation types that are popular in a variety of installations for the entire building envelope: EPS and XPS

 

With today’s design-oriented goals of sustainability and energy efficiency, the proper use of insulation is becoming more important than ever. There are many different ways to insulate a building, and there are dozens of insulation assemblies in existence. This particular article focuses on two insulation types that are popular in a variety of installations for the entire building envelope: EPS and XPS.

Expanded polystyrene (EPS) foam is a closed-cell insulation that’s manufactured by “expanding” a polystyrene polymer; the appearance is typically a white foam plastic insulation material (the likes of which can be found as merchandise packaging). Extruded polystyrene (XPS) foam is a rigid insulation that’s also formed with polystyrene polymer, but manufactured using an extrusion process, and is often manufactured with a distinctive color to identify product brand.

Pros and Cons of EPS and XPS

Pros:

  • Recyclable products that assist with LEED points.
  • Won’t support mold or mildew growth.
  • Long-term, stable R-value.
  • Can be placed below grade.
  • Can be utilized for inverted assemblies (over membrane).

Cons:

  • Exposure to sun will deteriorate the product.
  • Solvents/solvent-based materials cause irreversible damage.
  • Elevated temperatures (above 250 degrees F.) will “melt” polystyrene.
  • Incompatible with certain thermoplastics, polystyrene insulations are known to draw plasticizers out of thermoplastic membranes, causing permanent degradation.
  • Polystyrene is flammable, requiring proper placement in any assembly.
While EPS and XPS are two different products, they do have some similar characteristics and fall under the same manufacturing standard: ASTM C578 Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation. This particular specification covers the different types and physical properties of cellular polystyrene intended for use as thermal insulation.

Polystyrene insulation materials that fall under ASTM C578 fall into several different classifications: Type I through Type XII (with the exception of Type III, which is no longer available). The different classifications relate directly to physical characteristics of each type – most notably, the density, compressive resistance, and R-value. The range in densities and compressive strengths allows for specific uses on different parts of a building.

Polystyrene insulation is manufactured in a variety of board sizes – usually a minimum of 1-inch thick. Tapered units are also manufactured for use in roofing assemblies where the insulation is used to create slope for positive drainage. One of the more common uses in roofing is the ballasted single-ply roof assembly, where a roof membrane is placed over the insulation and ballasted with rock, concrete pavers, or other material.

Polystyrene insulations can be used in asphalt built-up roofing systems; however, provisions must be made to protect the insulation from heat (i.e. hot bitumen or torch) and solvent-based products (i.e. adhesives). In addition, certain thermoplastic roof membranes require a separation layer between the layer of insulation and the membrane.

EPS and XPS are resistant to moisture; however, XPS is more common for below-grade waterproofing and roof systems where insulation is placed over the roof membrane (IRMA, or inverted roof membrane assembly). The IRMA concept is also utilized for insulating building walls, where polystyrene insulation is placed over a barrier membrane, with the siding or cladding system installed over the insulation layer.

The use of EPS and XPS insulation in building construction offers great flexibility, compatibility, and thermal efficiency for use at all areas of a building envelope. Picking between the two will depend on particular use; choosing the appropriate type is critical for proper insulation performance.

Steven L. McBride is president at Portland, OR-based Professional Roof Consultants Inc.

 


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Visit our website today to learn about the design flexibility of a Morton building and the endless possibilities of partnering with our designBUILD team.


Wood construction is both cost and energy efficient. Check out Morton Buildings and our designBUILD team online today to discover all the benefits of post-frame construction.


When choosing a metal-clad building for your next construction project, consider Morton Buildings, Inc., and their designBUILD team, we’ll make your dream a reality.

We Can Help You Reduce Energy by 30%

Our mission is to help our customers manage their buildings' energy costs, improve reliability, and enhance performance while having a positive impact on the environment.
CLICK HERE to find out how.

 

Add highly responsive multi-zone comfort to any building project, in any climate. Our CITY MULTI H2i R2- and Y-Series VRF systems give you flexibility to fit the needs of any building. Enjoy 100% heating capacity at 0°F outdoor ambient, and 85% heating capacity at -13°F outdoor ambient.  For more information, log on to www.mitsubishipro.com


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Tennant Company is a recognized leader in designing, manufacturing and marketing solutions that help create a cleaner, safer, healthier world. With thousands of satisfied customers already using award winning ec-H2O technology, why not see what you're missing? Test ec-H2O on your soils in your facility. Get a free demo.

 

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