What R-Value Does and Does Not Tell You
| Concept | What it means | What to ask |
|---|---|---|
| R-value | Measures resistance to heat flow, not a complete description of assembly performance. | Ask for product-specific documented design. |
| Nominal vs assembly | Published product data and whole-assembly performance are not the same. | Request documentation for the actual foam and assembly. |
| Air sealing | Spray foam can insulate and air-seal, but product and assembly decide suitability. | Ask how air sealing is included in the written scope. |
Thickness Belongs in a Product-Specific Plan
R-value measures heat resistance. Products differ, and nominal product data is not the same as whole-assembly performance.
Air sealing also matters. Both open-cell and closed-cell foam can insulate and air-seal, but suitability depends on the product and assembly.
BASF publishes product-specific thermal and air/moisture properties for its WALLTITE family. That illustrates why a quote should name the actual foam product.
There is no universal two-inch or three-inch recommendation. Ask for documented design values for the product and assembly proposed for your property.
Questions About R-Value and Thickness
- Which foam product is specified, and where can I read its published properties?
- Is the quoted R-value based on product data or whole-assembly performance?
- What thickness is proposed, and what is that based on?
- How does the scope handle air sealing separately from thermal resistance?
- Will the installer document coverage and final thickness?
- What assembly details affect performance in my attic, wall or crawlspace?
- What is the next step if the proposed product does not fit the assembly?
A FEW MORE ANSWERS
Questions before you get started
Is a higher R-value always better?
R-value measures heat resistance, but more is not automatically the right answer for every assembly. Moisture, air sealing, thickness and product approval also matter.
How thick should spray foam be?
There is no universal thickness. Ask for a product-specific documented design that names the foam, the assembly and the basis for the proposed thickness.
Does spray foam air-seal as well as insulate?
Both open-cell and closed-cell foam can insulate and air-seal, but product and assembly decide suitability. The written scope should state how air sealing is included.