XPS vs EPS: Product Comparisons & Value Engineering

It's important to understand the differences between XPS and EPS foam board in continuous insulation (ci) exterior wall systems.

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.

Advanced Insulated Wall Systems that Exceed Expectations and Code

StoTherm ci XPS is a continuous insulation system, which provides air, thermal and moisture control without the connection and compatibility challenges that characterize other systems, while also offering multiple design and finish options.

Today’s architects, specification professionals, and owners are typically looking for an insulated wall design that not only meets but exceeds the nation’s increasingly demanding code requirements. Enter the StoTherm® ci XPS continuous insulation system, which provides air, thermal and moisture control without the connection and compatibility challenges that characterize other systems, while also offering multiple design and finish options.

As the building industry adopts more stringent energy codes (Title 24, IBC, IECC, ASHRAE 90.1), the need for external insulated finish systems (EIFS) is increasing. The StoTherm ci system is highly energy efficient, minimizing heating and cooling costs while reducing greenhouse gas emissions. The components prevent thermal bridging, thus lowering the risk of heat leakage and the attendant energy loss.

Other features that make the StoTherm ci XPS system a superior alternative to other systems include:

  • Durability and impact resistance (77% higher density and 250% higher compressive resistance than EPS)
  • Low Water Absorption (due to its closed cell structure)
  • R-Value of R5/inch (the higher the R-value, the greater the resistance to heat flow)

The system is also installation friendly; one installer and a single skilled trade person can make quick work of it. The low allowable deflection value makes for lightweight construction, which reduces overall project cost and weight per square foot.  These factors make for material and labor costs that are highly competitive, if not more economical than most other options.

A wide range of decorative and protective wall finishes (StoCreativ® Brick, granite, limestone) along with unlimited color choices make StoTherm ci XPS is one of the most versatile and innovative products on the market today.

Look for the second part in this series next week, which explores other advances in durable insulation products offered by industry leaders and several case studies that demonstrate their value add for building professionals and owners.

Sto EIFS & Element Music Row Featured by EIMA

The new Element Music Row -- a luxury apartment high rise in Nashville -- used StoTherm ci Essence to ensure the building's energy efficiency.

One of Sto Corp’s signature exterior insulation finish projects is now being featured as a case study on the EIMA website.

Last year, working with Southern Wall Systems and Humphreys & Partners Architects, Sto helped incorporate a continuous exterior insulation system, and a continuous air and moisture barrier with high-performance finishes to protect the new Element Music Row highrise in midtown Nashville. The $100 million luxury apartment complex, is a 19-story, 431-unit building located in the heart of the country & western music capital of the world. The upscale new residence offers commanding views of downtown Nashville and easy access to all the shopping, dining and entertainment on Music Row.

StoTherm ci Essence – a decorative and protective exterior wall cladding that combines superior air and weather tightness with excellent thermal performance and durability – was the wall system of choice for the new structure, ensuring the building’s energy efficiency, aesthetics, and air-moisture control. Because of the inclusion of Sto products and other energy saving efforts, the developers are showcasing the building as a model “green living” environment that is, in fact, LEED certified.

The Element is located on Demonbreun (pronounced de-MUN-bree-un) Street in Nashville – an area that has become a symbol of urban revitalization for the music capital and a favorite venue for the city’s young, plugged-in professionals.  Private development is booming in the area, and developers like Element’s Childress Klein out of Charlotte, N.C. are looking to build upscale living spaces, Class A office buildings and tourist destinations.

For more information:


Three Part Series on Exterior Walls

The science of exterior walls has been well-documented; look for our three-part series that starts next week.

Starting next week, ARCHITRENDS is launching a three-part series on building better walls, thanks to a big assist from the Building Science Corporation (BSC) – a consulting and full-service architecture firm for commercial, institutional and residential buildings. An internationally recognized organization, BSC’s focus is preventing and resolving problems related to building design, construction and operation. Probably best known for their expertise in moisture dynamics, indoor air quality and forensic investigations into building failure, BSC advocates for sustainable design, energy efficiency and environmental responsibility in building technology. Their website www.Buildingscience.com  is a free online resource.

Better Walls for Buildings

The perfect wall is an environmental separator—it must keep the outside out and the inside in.  Therefore, in a world of perfects walls, a wall assembly must control rain, air, vapor and heat. Functional, resilient walls need four principal control layers:

  • moisture control layer
  • air control layer
  • vapor control layer
  • thermal control layer

As BSC points out, if you can’t keep the rain out, don’t waste your time on the air. If you can’t keep the air out, don’t waste your time on the vapor and forget about thermal. The perfect wall includes a water control layer, with an air control layer and vapor control layer positioned directly on the structure, and a thermal control layer covering the other control layers.

Expansion, contraction, corrosion, decay, ultra violet radiation (basically, most bad things!) are all functions of variations in temperature. So, control layers need to go on the outside to help the structure weather temperature extremes and protect it from water in its various forms, as well as ultra violet radiation.

The “clever” wall, as BSC calls it, uses building material that combines all four controls. Thus, air moisture barrier systems (AMBs) and exterior insulation finish systems (EIFS). The most “clever” walls utilize integrated, stand-alone systems that can work together to form a waterproof air barrier for all types of vertical, above-grade wall surfaces, engineered for fast, easy application. (Example: StoGuard) These continuous-insulation (ci) wall systems can provide superior air and weather tightness, long-lasting thermal performance, durability and are available in a wide range of decorative and protective finishes.

Look for PART ONE in our series next week; it will focus on Moisture Control.

When it Comes to EIFS, Mesh Matters

Mesh is one of the most important components in an effective EIFS installation.

We’re all familiar with the power that comes from teamwork, including the teamwork involved in constructing buildings. Whether its design, systems, skilled labor or the products used in construction – all the pieces need to fit together to form a cohesive structure.  Like all teams, there is always a member that helps strengthen the group and allows contributors to perform better. For EIFS (Exterior Insulation and Finish Systems) that critical impact player, providing additional team support, comes in the form of reinforcing mesh.

EIFS are typically made up of several different layers, and reinforcing mesh is one of the strongest components enhancing the performance, durability and aesthetics of the system. Mesh works a bit like a bulletproof vest:  the network of fibers in the vest works together to redistribute and absorb the impact of a bullet. Mesh helps redistribute stresses on a wall surface more evenly, thus providing additional strength.

Mesh forms the center of the EIFS defense in a fire or a Category 5 hurricane, assuming it is mesh that has passed a barrage of third-party EIFS testing — from NFPA 285 (fire performance testing) to Miami-Dade County Hurricane testing. It is incumbent on EIFS manufacturers to test and qualify all components of their systems to ensure the safety compliance and performance resilience of a building. And it’s just as important for EIFS installers to be a part of the team, to only use tested,  proven mesh products and to follow instructions for proper installation of the mesh.

Can Green Buildings Make Us Smarter?

Green is good -- outside or inside an occupied building.

A recent study published by Environmental Health Perspectives (EHP) suggests that Green Buildings create optimized conditions for health and productivity. In a series of experiments, indoor environmental quality (IEQ) factors for both “green” and “conventional” buildings were simulated in a controlled environment that included office workers, and the researchers measured variables such as carbon dioxide variation, ventilation and exposure to volatile organic compounds in the building atmosphere.

The results? On average, cognitive scores for the two groups of workers were 61% higher for those working in a building with green features than with conventional construction.  In other words, green building can potentially deliver a smarter workforce.