EPS Insulation: Below Grade

Energy efficient structures are becoming a part of today’s society when building new homes and apartments. When building, many aspects are take into account; a key component is insulating walls and ceilings.

What about insulating foundation walls and below ground floor slabs? One of the ways to do so is using EPS or XPS insulation.  

The article, “Help Your Customers Understand Below Grade Insulation” by Tom Savoy gives insights why below grade insulation matters; it helps reduce heating cost and prevents moisture problems, insect infestation, radon infiltration in addition to helping minimize the annoying and expensive fixes to protect concrete cracking, spalling and frost heave. Astonishingly,  lack of insulation in a building’s foundation and floor slabs account for and up to 25% of a building’s total energy loss, according to the EPS Industry Alliance.

When insulating below grade, it is important to analyze and know the moisture resistance and thermal performance (R-Value). For moisture resistance, EPS likes to absorb small amounts of moisture quicker, but releases it faster than XPS. It is said that XPS comes out ahead in the laboratory, while EPS is superior in real-world applications… choose wisely.  

The EPS and XPS insulation is put through a series of tests and evaluated per ASTM 272 (Standard Test Method for Water Absorption of Core Materials for Sandwich Constructions). ASTM 272 fully submerges the insulation in water for 24 hours then weighed for moisture absorption upon removal. It is not “real-world” building conditions, but ensures products are manufactured to required specifications. In-the-field tests show that EPS outperforms XPS because EPS dries faster than XPS. A real-world example, EPS and XPS were buried side by side for 15 years on a building in St. Paul, Minnesota. When the insulation was removed the EPS was four times drier than the XPS, EPS had only 4.8% moisture by volume compared to 18.9% moisture content for XPS. R-value had a result supporting EPS outperforms XPS in real-world application.  

The versatility of EPS is the most well-known and appreciated properties of foam plastic. When choosing EPS or XPS, EPS has become popular with contractors because of cost effectiveness, high-performing below-grade application, and with research, like above, EPS will provide the best exterior insulation results for the price.

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