Extruded Polystyrene (XPS) Insulation
Extruded polystyrene (XPS) rigid foam insulation is recognized by its distinctive blue, pink, or green color depending on the manufacturer. It is manufactured through a continuous extrusion process that produces a uniform closed-cell structure with excellent moisture resistance. XPS is the preferred rigid insulation for below-grade applications including basement walls and under-slab installations because it maintains its R-value and structural integrity even when exposed to moisture and soil contact. The consistent R-5 per inch rating makes thickness calculations straightforward. XPS boards are available in thicknesses from half an inch to 4 inches and common sheet sizes of 4 by 8 feet and 2 by 8 feet.
Extruded Polystyrene (XPS) Specifications
Best Applications for Extruded Polystyrene (XPS)
Extruded Polystyrene (XPS) is recommended for the following building components. Each application link shows the specific R-value requirements by climate zone and how Extruded Polystyrene (XPS) compares against other insulation options for that component.
Thickness Required by Climate Zone
The table below shows the thickness of Extruded Polystyrene (XPS) needed to achieve the DOE recommended R-value for each building component in every climate zone. Cells showing "N/R" indicate that insulation is not required for that component in that zone. Use this table to quickly determine how much Extruded Polystyrene (XPS) you need for your specific zone and application.
| Zone | Attic | Wall Cavity | Wall Cont. | Floor | Basement | Crawlspace | Cathedral | Garage |
|---|---|---|---|---|---|---|---|---|
| Zone 1 | 6" | 2.6" | N/R | 2.6" | N/R | N/R | 4.4" | 3.8" |
| Zone 2 | 7.6" | 2.6" | N/R | 2.6" | N/R | N/R | 4.4" | 3.8" |
| Zone 3 | 7.6" | 2.6" | N/R | 3.8" | 1" | 1" | 6" | 3.8" |
| Zone 4 | 9.8" | 2.6" | 1" | 5" | 2" | 2" | 7.6" | 6" |
| Zone 5 | 9.8" | 2.6" | 1" | 5" | 2" | 2" | 7.6" | 6" |
| Zone 6 | 12" | 2.6" | 2" | 5" | 3" | 2" | 9.8" | 7.6" |
| Zone 7 | 12" | 2.6" | 2" | 5" | 3" | 2" | 9.8" | 7.6" |
| Zone 8 | 12" | 2.6" | 3" | 5" | 3.8" | 2" | 9.8" | 7.6" |
Cost Estimates by Climate Zone (per 1,000 sq ft)
Material cost estimates for Extruded Polystyrene (XPS) at the DOE recommended R-value for each climate zone and component. These are material costs only and do not include labor. Professional installation typically adds 30-50% to the material cost shown below.
| Zone | Attic | Wall Cavity | Wall Cont. | Floor | Basement |
|---|---|---|---|---|---|
| Zone 1 | $5,400 | $2,340 | N/R | $2,340 | N/R |
| Zone 2 | $6,840 | $2,340 | N/R | $2,340 | N/R |
| Zone 3 | $6,840 | $2,340 | N/R | $3,420 | $900 |
| Zone 4 | $8,820 | $2,340 | $900 | $4,500 | $1,800 |
| Zone 5 | $8,820 | $2,340 | $900 | $4,500 | $1,800 |
| Zone 6 | $10,800 | $2,340 | $1,800 | $4,500 | $2,700 |
| Zone 7 | $10,800 | $2,340 | $1,800 | $4,500 | $2,700 |
| Zone 8 | $10,800 | $2,340 | $2,700 | $4,500 | $3,420 |
Advantages and Limitations
Every insulation type has trade-offs that affect its suitability for different applications. Understanding these trade-offs helps you select the right insulation for your specific project requirements, budget, and installation constraints.
Advantages of Extruded Polystyrene (XPS)
- High R-value per inch reduces required thickness
- Suitable for DIY installation, reducing labor costs
- Excellent moisture resistance for wet or below-grade applications
- Well-suited for: Basement Wall, Crawlspace, Wall Continuous (Exterior), Floor (Over Unconditioned Space)
Limitations of Extruded Polystyrene (XPS)
- Combustible material requires thermal barrier coverage in occupied spaces
Compare Other Insulation Types
Browse specifications and cost analysis for other insulation materials to find the best option for your project.