How much Attic Insulation is enough?

In Boise, Idaho, the recommended amount of attic insulation typically depends on the type of insulation used (e.g., fiberglass batt, spray foam, cellulose) and the desired R-value. The R-value measures insulation’s resistance to heat flow—the higher the R-value, the better the insulation’s performance.

For Boise, which falls under USDA climate zone 5, the general recommendations are:

Fiberglass or Cellulose Insulation (Loose-fill or Batt)

R-value between 49 and 60 is recommended for attics in Boise. Currently Ada County specifies that homes must have R-38 or greater to meet building code.

R-49 is often considered a baseline for good insulation performance in this region.

R-60 offers extra insulation and can be beneficial if you are aiming for higher energy efficiency.

Spray Foam Insulation

• Spray foam typically has a higher R-value per inch compared to batt or blown-in insulation. To achieve similar performance, you might only need about 6 to 8 inches of spray foam (depending on the specific product used), achieving an R-value between R-49 to R-60.

Why R-49 to R-60?

• Boise’s cold winters and hot summers make attic insulation essential for maintaining a comfortable indoor temperature and for reducing energy bills.
• Insufficient insulation can lead to heat loss in the winter and heat gain in the summer, driving up heating and cooling costs.

Other Considerations

• If your attic already has some insulation, it’s possible to add more to bring it up to the recommended R-value.
• Insulation should be evenly distributed across the attic floor, without gaps or compression, to ensure maximum efficiency.

If you are unsure about your current insulation levels, a professional energy audit can provide a more accurate recommendation tailored to your specific home and insulation type.  Give 3e Insulation a call at 208-477-4547 to schedule your free energy audit.