Differences in R-values with fiberglass insulation

Fiberglass insulation is one of the most commonly used types due to its balance of cost, effectiveness, and ease of installation. Here are some key differences and considerations regarding R-values with fiberglass insulation:

Types of Fiberglass Insulation:

• Batts and Rolls: These are pre-cut to fit standard wall stud and attic joist spacings. Their R-value per inch typically ranges from R-2.9 to R-3.8. The exact R-value can depend on the thickness, density, and whether it’s faced (with a vapor barrier) or unfaced.
• Blown-in or Loose-Fill Fiberglass: Used in attic spaces or hard-to-reach areas, it has an R-value around R-2.2 to R-2.7 per inch when installed at the recommended density. However, if not installed to the correct density, its R-value can decrease.

 

Installation Quality:

• Compression: If batts or rolls are compressed to fit into a smaller space than intended, their R-value decreases because the air pockets that provide the insulation are squeezed out. For example, compressing a batt designed for a 3.5-inch space into a 2-inch space can significantly reduce its effectiveness.
• Gaps and Coverage: Any gaps or areas not covered by insulation will act as thermal bridges, reducing the overall R-value of the installation. Proper coverage is crucial.

 

Settling Over Time:

• Unlike some other materials, fiberglass insulation doesn’t settle much over time. However, if it’s not installed to the correct depth or density initially, settling can occur, slightly reducing the R-value.

 

Environmental Factors:

• Moisture: Fiberglass insulation loses some of its R-value when it gets wet. However, once it dries out, it can regain most of its insulating properties, though there might be a slight permanent reduction.
• Temperature: Fiberglass insulation’s R-value is relatively stable across a wide range of temperatures, making it reliable in various climates.

 

R-Value vs. Real-World Performance:

• Air Leakage: Fiberglass insulation does not stop air movement. If there are significant air leaks in the building envelope, the effective R-value can be much lower than the stated value due to convective heat loss.
• Thermal Bridging: Wooden studs or metal components in walls conduct heat more than fiberglass, reducing the effective R-value of a wall or ceiling. This is why some modern constructions use continuous insulation methods or add extra insulation at these points.

 

Comparison with Other Insulations:

• Versus Spray Foam: Closed-cell spray foam has a higher R-value per inch (R-6 to R-7) and also acts as an air barrier, potentially offering better real-world performance despite higher initial costs.
• Versus Cellulose: Cellulose might offer slightly higher R-values per inch when installed correctly (R-3.1 to R-3.7), but it’s denser and can be more effective at reducing air leakage.

 

Practical Considerations:

• Cost: Fiberglass is generally less expensive than many other high-R-value materials, making it a popular choice for budget-conscious projects.
• Health and Safety: Proper handling is required due to the potential for skin irritation or respiratory issues from glass fibers.

 
When choosing fiberglass insulation, consider not just the R-value but also how it’s installed, the overall building design, and whether additional measures (like air sealing) are implemented to maximize its effectiveness. If you’re looking into the latest products or specific applications, checking recent product data might give you the most current R-values or innovations in fiberglass insulation technology.