What is the Continuous Rvalue of 2 Ridgid Insulation
Rigid insulation like rigid foam and foam boards have high R-values. That's why materials like polyiso (polyisocyanurate), EPS (expanded polystyrene), and XPS ( extruded polystyrene) like Styrofoam make for such good insulation materials. We are going to look what is rigid insulation R-value per inch and the rigid insulation thickness chart (for 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10-inch foam boards).
Namely, we will look into 3 main types of rigid insulation:
- R-values of EPS. EPS stands for Expanded PolyStyrene. We differentiate between higher R-value high-density EPS and lower R-value low-density EPS.
- R-values of XPS (also known as Styrofoam). XPS stands for eXtruded PolyStyrene. The same as with EPS, we differentiate between higher R-value high-density XPS and lower R-value low-density XPS.
- R-values of ISO (also known as polyiso). ISO is an abbreviation of polyISOcyanurate. This is foil-faced polyisocyanurate; the R-value of ISO decreases over the years.
R-values for rigid insulation vary from R-3.85 to R-6.8 per inch of thickness. Polyiso has the highest R-value, followed by XPS and EPS. The key to all rigid insulation high R-values are small air pockets that exhibit high thermal resistivity properties:
Altogether we are going to check out 5 relevant charts for rigid insulation R-values:
- We will start with the list of the R-values of these rigid insulations per inch of thickness (Chart 1).
- After that, we are going to look at rigid insulation thickness charts for EPS, XPS, and ISO at various thicknesses (Chart 2, Chart 3, and Chart 4).
- Additionally, we will look at how thick rigid insulation we need to achieve R10, R20, R30, and R49 insulation value (Chart 5).
Note: Rigid insulation boards are commonly manufactured in 2×4, 4×4, and 4×8 board sizes. Nonlaminated boards have thicknesses of 0.5, 0.75, and 1 inches. Laminated boards have thicknesses of 0.5, 1, and 2 inches.
Let's start with the specified per inch R-value of rigid insulation:
Rigid Insulation R-Value Per Inch (Chart 1)
| Rigid Insulation Material: | Insulation R-Value Per Inch: |
| High-Density EPS | R-4.2 Per Inch |
| Low-Density EPS | R-3.85 Per Inch |
| High-Density XPS | R-5.2 Per Inch |
| Low-Density XPS | R-4.15 Per Inch |
| ISO (Penthane Expanded, New Polyiso) | R-6.8 Per Inch |
| ISO (Penthane Expanded, 5-10 Years Old Polyiso) | R-5.5 Per Inch |
As you can see, polyiso has the highest rigid insulation R-value. A new polyiso will have an R-value of R-6.8 per inch. This is a 31% higher R-value than high-density XPS and a 62% higher R-value than high-density EPS.
It is worth noting that the thermal resistance of ISO degrades in time. Within 5 to 10 years, the R-value of polyiso will likely fall from R-6.8 to R-5.5. This is a 24% drop in R-value.
High-density XPS has an R-value of 5.2 per inch; low-density XPS has an R-value of 4.15 per inch. Styrofoam is a trademark name for XPS; the R-value of Styrofoam is 5.2 per inch since it is a high-density XPS.
High-density EPS has an R-value of 4.2 per inch; low-density EPS has an R-value of 3.85 per inch.
If you compare the high-density R-value of XPS and EPS, you can see that XPS has a 24% higher R-value per inch than EPS.
Both XPS and EPS are made out of the same material: polystyrene. The difference in thermal resistivity is due to how this polystyrene is manufactured. XPS is made using the process known as extrusion; producing a closed-cell tightly packed structure. EPS is made using an expansion process where beads of foam are made to expand and fuse together.
Now, knowing the R-values per inch of thickness will help us determine what R-values 2-inch, 3-inch, 4-inch, and so on rigid insulation boards have. We will start with ISO boards (Chart 2), and proceed to XPS boards (Chart 3) and EPS boards (Chart 4):
ISO Thickness R-Value (Rigid Insulation Chart 2)
Given that the R-value per inch of ISO is time-dependent, we use an R-5.8 per inch as a median insulation metric in this chart:
| ISO Thickness: | R-Value: |
| 1 Inch ISO Board | R-5.8 |
| 1.5 Inch ISO Board | R-8.7 |
| 2 Inch ISO Board | R-11.6 |
| 2.5 Inch ISO Board | R-14.5 |
| 3 Inch ISO Board | R-17.4 |
| 3.5 Inch ISO Board | R-20.3 |
| 4 Inch ISO Board | R-23.2 |
| 4.5 Inch ISO Board | R-26.1 |
| 5 Inch ISO Board | R-29.0 |
| 5.5 Inch ISO Board | R-31.9 |
| 6 Inch ISO Board | R-34.8 |
| 6.5 Inch ISO Board | R-37.7 |
| 7 Inch ISO Board | R-40.6 |
| 7.5 Inch ISO Board | R-43.5 |
| 8 Inch ISO Board | R-46.4 |
| 8.5 Inch ISO Board | R-49.3 |
| 9 Inch ISO Board | R-52.2 |
| 9.5 Inch ISO Board | R-54.5 |
| 10 Inch ISO Board | R-58.0 |
Let's say we are looking for an R-value of a 2-inch ISO foam board. You can check this chart and see that a 2-inch ISO foam board has an R-value of R-11.6.
If you have a rigid ISO foam board that is more than 9 inches thick, you can expect that the R-value of such board will be over R-50. This is more than enough even for attics (the best attic insulation is usually R-49).
Let's check XPS and EPS charts as well:
XPS Thickness R-Value (Rigid Insulation Chart 3)
Here we use the R-value of high-density Styrofoam or XPS of R-5.2 per inch:
| ISO Thickness: | R-Value: |
| 1 Inch XPS Foam Board | R-5.2 |
| 1.5 Inch XPS Foam Board | R-7.8 |
| 2 Inch XPS Foam Board | R-10.4 |
| 2.5 Inch XPS Foam Board | R-13 |
| 3 Inch XPS Foam Board | R-15.6 |
| 3.5 Inch XPS Foam Board | R-18.5 |
| 4 Inch XPS Foam Board | R-20.8 |
| 4.5 Inch XPS Foam Board | R-23.4 |
| 5 Inch XPS Foam Board | R-26 |
| 5.5 Inch XPS Foam Board | R-28.6 |
| 6 Inch XPS Foam Board | R-31.2 |
| 6.5 Inch XPS Foam Board | R-33.8 |
| 7 Inch XPS Foam Board | R-36.4 |
| 7.5 Inch XPS Foam Board | R-39 |
| 8 Inch XPS Foam Board | R-41.6 |
| 8.5 Inch XPS Foam Board | R-44.2 |
| 9 Inch XPS Foam Board | R-46.8 |
| 9.5 Inch XPS Foam Board | R-49.4 |
| 10 Inch XPS Foam Board | R-52 |
Styrofoam, for example, is a trademark name for high-density XPS foam boards. You can get 2-inch, 3-inch, 4-inch Styrofoam, and so on.
2-inch Styrofoam has a typical insulation R-value of R-10.4. You can check XPS R-values for different thicknesses from the chart above.
EPS Thickness R-Value (Rigid Insulation Chart 4)
Here are R-values for different thicknesses of high-density EPS:
| ISO Thickness: | R-Value: |
| 1 Inch EPS Foam Board | R-4.2 |
| 1.5 Inch EPS Foam Board | R-6.3 |
| 2 Inch EPS Foam Board | R-8.4 |
| 2.5 Inch EPS Foam Board | R-10.5 |
| 3 Inch EPS Foam Board | R-12.6 |
| 3.5 Inch EPS Foam Board | R-14.7 |
| 4 Inch EPS Foam Board | R-16.8 |
| 4.5 Inch EPS Foam Board | R-18.9 |
| 5 Inch EPS Foam Board | R-21 |
| 5.5 Inch EPS Foam Board | R-23.1 |
| 6 Inch EPS Foam Board | R-25.2 |
| 6.5 Inch EPS Foam Board | R-27.3 |
| 7 Inch EPS Foam Board | R-29.4 |
| 7.5 Inch EPS Foam Board | R-31.5 |
| 8 Inch EPS Foam Board | R-33.6 |
| 8.5 Inch EPS Foam Board | R-35.7 |
| 9 Inch EPS Foam Board | R-37.8 |
| 9.5 Inch EPS Foam Board | R-39.9 |
| 10 Inch EPS Foam Board | R-42 |
Example: What is the 2-inch EPS foam board R-value? Check the chart above and you can see that the R-value of a 2-inch EPS foam board is R-8.4.
In many cases, however, you want to know how thick rigid insulation you need to achieve R-10, R-20, R-30 insulation value, and so on. In this last chart we have calculated how many inches of rigid insulation you need for certain R-value with new ISO boards, high-density XPS, and high-density EPS:
R-10, R-20, R-30, and R-49 Rigid Insulation Thickness Chart (Chart 5)
Let's say you want your walls to have an R-30 value. How many inches of XPS, EPS, or ISO do you need? Here is a chart for R-10, R-20, R-30, and R-49 insulation values that will tell you how many inches of rigid insulation of the specified type you need:
| Rigid Insulation Type: | Thickness For R-10: | Thickness For R-20: | Thickness For R-30: | Thickness For R-49: |
| High-Density EPS | 2.38 Inches | 4.76 Inches | 7.14 Inches | 11.67 Inches |
| Low-Density EPS | 2.60 Inches | 5.19 Inches | 7.79 Inches | 12.73 Inches |
| High-Density XPS | 1.92 Inches | 3.85 Inches | 5.77 Inches | 9.42 Inches |
| Low-Density XPS | 2.41 Inches | 4.82 Inches | 7.23 Inches | 11.81 Inches |
| ISO (Penthane Expanded, New Polyiso) | 1.47 Inches | 2.94 Inches | 4.41 Inches | 7.21 Inches |
| ISO (Penthane Expanded, 5-10 Years Old Polyiso) | 1.82 Inches | 3.64 Inches | 5.45 Inches | 8.91 Inches |
Here you can see that the R-value of 2-inch rigid insulation is higher than R-10 if you use ISO or high-density XPS.
The higher the R-value of rigid insulation, the less thick foam board you will need to achieve the same insulation R-value.
Hopefully, this illustrates how to think about the R-values of rigid insulation. If you have any questions, you can use the comments below and we will try to help you out.
You can also consult R-value charts for other insulation materials here. To adequately understand all types of insulation we use in building houses, you should check the explanation of 9 types of insulation here.
Source: https://learnmetrics.com/rigid-insulation-r-value-per-inch-eps-xps-iso-thickness-charts/
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