Insulating below-grade with high-performing expanded polystyrene

Due to its versatility, building professionals can cut rigid foam into sheets, slabs, or any desired shape to meet specific below-grade needs, whether commercial or residential.
Due to its versatility, building professionals can cut rigid foam into sheets, slabs, or any desired shape to meet specific below-grade needs, whether commercial or residential.

EPS’ thermal properties

Aside from an increased likelihood for higher moisture levels than above-grade areas, below-grade applications are also susceptible to energy loss, requiring proper insulation to optimize efficiency. Generally speaking, the higher an R-value, the greater the insulating effectiveness, so below-grade insulation solutions must post high thermal resistance over the long-term to ensure energy savings.

EPS’ thermal properties help lay the foundation for high and stable R-values, making it an attractive option for the below-grade builder. The rigid foam is composed of 98 percent air, as air does not leech out of the cellular structure throughout the product’s time in service. This results in stable, reliable insulation performance, and it is not uncommon for EPS manufacturers to warranty R-values for 20 years, guaranteeing lasting thermal performance.

EPS’ mechanical properties

As for mechanical properties, EPS’ resistance to compressive stresses can align with foundation load requirements. Contrary to popular belief, concentrated loads applied to a concrete slab do not transfer directly to the sub-grade below. Instead, concrete slabs disperse loads evenly, meaning the insulation can have a lower compressive strength and still comply with below-grade building codes.

With a compressive resistance resting between 69 to 414 kPa (10 to 60 psi), manufacturers can produce EPS to meet strength requirements of multiple building codes. For example, for foundation “applications in which the foam insulation bears a minimal load, ASTM C578 [Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation] Type I (nominal density of 14 kg/m3 [0.9 lb per cf]) material is adequate. EPS board produced to meet the requirement of Type I EPS has been tested and found to fall within 69 to 96 kPa (14 psi). The resilience of EPS insulation board provides reasonable absorption of building movement without transferring stress to the interior or exterior finish at the joints,” says EPS-IA.

Bearing this in mind, builders and contractors can satisfy below-grade insulation requirements with EPS without over-engineering, leading to material savings.


These attributes of EPS insulation—mitigation of moisture, enduring R-values, and compressive strength—are evident in numerous real-world below-grade applications. From increasing energy efficiency in an Albuquerque perishable food warehouse, New Mexico, to insulating foundations to ensure military personnel are sheltered in warm, comfortable housing near the Arctic Circle, construction teams seek out EPS commercially and residentially.

EPS keeps perishables fresh in Albuquerque warehouse

Energy-conserving insulation is crucial in places such as sun-drenched, arid Albuquerque, New Mexico. With daytime temperatures often exceeding 38 C (100 F) in the summer months, Albuquerque builders are in a constant battle to keep buildings cool without sending energy costs through the roof. This struggle extends to all cold storage applications, including a food and nutrition services kitchen and storage warehouse designed to preserve produce and perishables used for student breakfasts, lunches, and snacks.

At 10,034 m2 (108,000 sf), this cold storage facility was central to the Albuquerque Public Schools’ (APS’) educational rebuild and remodel. To keep moisture at bay, provide consistent thermal performance to lower energy costs, and offer compressive strength, the project’s general contractor and commercial concrete contractor installed EPS rigid foam insulation below the facility’s concrete slab floor.

Cold storage warehouses located in climates like New Mexico run the risk of warm, outside air seeping into the space and coming into contact with colder building materials, resulting in added cooling cost and condensation. The presence of condensation in these environments can cause electronics to fail, goods to deteriorate, and harmful mold and bacteria to grow, in addition to compromising the building’s structural integrity. Building teams were able to sidestep these challenges thanks to EPS with premium, factory-applied laminate polymeric facers. The insulation and facer combination helps reduce the formation of condensation on foundation walls and keeps the droplets from entering into the rigid foam material, shielding the concrete foundation and slabs from moisture penetration.

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