RMax Below Grade 4ft x 8ft Insulation Board - All Sizes
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RMax Below Grade 4ft x 8ft Insulation Board - All Sizes

SKU: 776473-1P

Est Delivery between and .

Estimated Delivery Time Of 5-7 Working Days

Thickness Sq/Ft Per Pallet Sheets Per Pallet R Value
0.75 In 1920 60 R5
1 In 1536 48 R6
1.5 In 960 30 R10
2 In 767 24 R13.1
2.3 In 640 20 R15.3
3 In 512 16 R20.3


The RMax Below Grade 4ft x 8ft Insulation Board is a cutting-edge solution designed for a variety of below-ground insulation needs. Crafted from high-quality polyisocyanurate (polyiso) foam, this insulation board measures 96 inches in length and 48 inches in width, providing an ample coverage area of 32 square feet. The polyiso material is renowned for its exceptional thermal insulation properties, making this board an ideal choice for enhancing energy efficiency in below-grade exterior walls, blind side walls, under slab, and slab on grade applications. Its size and coverage capabilities ensure that large areas can be insulated efficiently, reducing the need for multiple pieces and seams that could compromise the insulation layer.

The construction of the RMax Below Grade Insulation Board features a polyiso foam core that is bonded to reinforced polymeric facers on both sides. This unique composition results in a closed-cell and closed matrix foam core that offers superior resistance to water absorption. The durable facers provide an additional layer of protection, especially important during the backfill process in below-grade installations. This multi-layered defense mechanism not only enhances the insulation's effectiveness but also extends its lifespan by guarding against moisture and physical damage. It's an optimal solution for those seeking a robust insulation system that maintains its integrity and performance over time.

Designed specifically for challenging environments, the RMax Below Grade Insulation Board excels in applications where moisture resistance and durability are critical. Its advanced material composition and thoughtful design cater to the specific needs of below-grade insulation, offering unparalleled energy efficiency and protection against the elements. Whether it's used for exterior walls that come into contact with the soil, blind side walls adjacent to earth-filled areas, insulation under concrete slabs, or in slab-on-grade constructions, this insulation board stands up to the task. It's an investment in energy efficiency and structural integrity, ensuring a comfortable and secure environment for years to come.

Pros & Cons

  • Exceptional thermal insulation efficiency due to polyiso foam core, enhancing energy savings and interior comfort.
  • Superior moisture resistance and durability, with a closed-cell foam core and reinforced facers that protect against water absorption and physical damage.
  • Large coverage area with dimensions of 4ft x 8ft, allowing for fewer seams and a more continuous insulation layer, thus improving overall thermal performance.
  • Potential higher upfront cost compared to traditional insulation materials, which might affect budget considerations for some projects.
  • Requires careful installation to maximize moisture resistance and thermal efficiency, possibly necessitating professional installation for optimal performance.
  • Limited flexibility in terms of cutting and fitting around irregular shapes, which may complicate installation in non-standard spaces.

Frequently Asked Questions

What is Polyiso insulation and why is it used for below-grade applications?

Polyiso (polyisocyanurate) insulation is a type of foam board insulation that offers high thermal resistance, making it ideal for saving energy and reducing heating and cooling costs. Its closed-cell and closed matrix structure provides excellent moisture resistance, making it suitable for below-grade applications where water exposure is a concern.

Can RMax Below Grade Insulation Board be used in all types of climates?

Yes, the RMax Below Grade Insulation Board is designed to perform effectively in a wide range of climates. Its high thermal resistance and moisture protection make it a versatile choice for both cold and warm climates, enhancing the energy efficiency of buildings in any location.

How does the RMax Below Grade Insulation Board contribute to energy efficiency?

By providing high thermal resistance, the RMax Below Grade Insulation Board reduces the amount of heat loss or gain through the building's foundation and walls. This leads to a more stable interior temperature, less energy consumption for heating and cooling, and consequently, lower energy bills.

Is professional installation required for the RMax Below Grade Insulation Board?

While professional installation is recommended to ensure the highest level of performance and moisture resistance, experienced DIYers can also install the RMax Below Grade Insulation Board by following proper installation guidelines. However, for complex projects or those requiring specific building codes compliance, professional installation is advised.

How does the RMax Below Grade Insulation Board handle moisture and prevent water damage?

The board's polyiso foam core is designed to resist water absorption, and its reinforced facers add an extra layer of moisture protection. This makes it highly effective at preventing water damage and maintaining its insulating properties in environments exposed to moisture.

Length 96 In
Width 48 In
Brand Rmax
Coverage 32 sq ft
Material Polyiso

Est Delivery between and .

Delivery will always take place on a weekday (Mon - Fri).
For information on delivery costs and more view our delivery info page.