Advanced Insulated Wall Systems — Part 2
As exterior insulation wall systems gain in popularity and demand, it’s important to differentiate between the options available to building professionals. The key words that count these days are “code compliance,” “continuous insulation,” “hydrophobicity,” “compressive strength,” and “R-Value.” Other desired benefits when comparing insulation for ci systems include moisture management, durability, and reduced energy costs.
While polystyrene-based insulation board products are often specified as part of a continuous insulation (ci) wall system, and some products may appear similar on the surface, the fact is, if you drill down into the science of insulated plastic sheeting, not all foam plastic insulations are the same.
A quick primer on the differences between XPS and EPS
Extruded polystyrene foam insulation (XPS) is a high-performance, closed-cell rigid insulation, manufactured in a proprietary process that melts plastic resin and additives into a molten material that is extruded through a die where it expands and cools into a uniform closed-cell, rigid foam insulation board with no voids or pathways for moisture to enter. It is, therefore, inherently moisture-resistant or, in scientific terms, “hydrophobic.”
Molded bead expanded polystyrene (EPS) is made from small foam beads that are placed in a mold. These beards are exposed to steam while in the mold, which causes the beads to expand and stick together. This method of manufacture can result in interconnected voids between the beads, and these gaps can potentially provide pathways for water to penetrate the insulation. It is, therefore, not nearly as moisture resistant as XPS and could lead to degradation of the insulation’s performance.
The differences in composition and structure between the two insulation types can obviously affect the ultimate long-term performance, durability and efficiency of a ci-system wall. And yes, XPS is a more expensive, up-front investment than EPS, but before you “value engineer” it out of a project, you may wish to consider the long-term savings and benefits of its molecular structure and formulation.
Is XPS insulation the right product for your next EIFS wall?
Make an informed decision. The superior water resistance and higher lifetime R-value for XPS make it a compelling product to consider, as its performance compares favorably to the more commonplace molded bead expanded polystyrene (EPS).
The cost savings for EPS can be tempting, but it is also more susceptible to moisture intrusion and therefore not as durable. Another drawback: its R-value is rated “medium” versus “high.” (R-value is the measure of thermal resistance; the higher the R-Value, the greater the energy savings.) That means higher energy costs will be required to maintain the comfort level for the building’s occupants.
While the initial cost of an XPS system needs to be considered, its attributes will pay dividends when accounting for future energy savings and protection from moisture intrusion. An XPS system is also lighter weight, which makes for a low allowable deflection value. This savings and the fact that an XPS system is installation friendly with just one installer and a single skilled trade person required, also offsets the product cost, making XPS a more competitive option.
So when you weigh the options and lean in the direction of durability and efficiency, XPS becomes the logical choice.