Understanding Spray Foam Insulation

Spray foam insulation can be divided into two main types: closed cell and open cell. Today, we’re focusing on closed cell spray foam due to its different chemistry and superior insulating properties. The insulation value in spray foam is primarily due to the blowing agent trapped in its cells, which transitions from a liquid to a gas during application, forming a cellular plastic structure. For closed cell foam, this agent is typically a form of freon.

R-Value and LTTR Standards

Closed cell spray foam typically has an R-value of about 6 per inch, which measures its thermal resistance. Unlike fiberglass insulation, spray polyurethane foam is rated according to an LTTR (Long-Term Thermal Resistance) standard. This means that the foam’s insulating properties are guaranteed to last, often up to 30 years, which is crucial for insurance and mortgage purposes.

Insulation Efficiency: The Data

Using an ASTM C236 guarded hotbox test, we can accurately measure the insulation efficiency of closed cell spray foam. Here’s a summary of the key findings:

• 0 Inches of spray foam: Efficiency of 0% heat reduction
• 1 inch of spray foam: Approximately R6, reducing 72% of heat.
• 2 inches of spray foam: Around R13, achieving 86% heat reduction.
• 3 inches of spray foam: About R19, providing 90% heat reduction.
• 4 inches of spray foam: Reaches around R27-28, with 92% heat reduction.

Key Insights on Spray Foam Thickness

1. Efficiency at 2 Inches: Two inches of closed cell spray foam offers an excellent balance, retaining 86% of heat, making it a highly efficient choice for most applications.
2. Diminishing Returns: Beyond three inches, the efficiency gains per additional inch are minimal. For example, increasing from three to four inches only boosts heat retention by 2%.
3. Cost-Effectiveness: Considering the diminishing returns, applying more than three inches is often not cost-effective. This understanding is crucial when evaluating insulation needs against budget constraints.

Conclusion

Understanding the efficiency and cost-effectiveness of closed cell spray foam insulation can help you make better decisions for your insulation needs. Remember, more isn’t always better due to the diminishing returns beyond a certain thickness.