Blown-In vs Fiberglass Attic Insulation
**Blown-in** insulation fills joist bays and odd cavities—great for retrofits. **Fiberglass batts** are cheaper per bag for open attics with uniform spacing but leave gaps if not cut carefully.
Step by step
1. Target R-value
Climate zone codes often want R-38 to R-60 in attics—measure depth.
2. Air seal first
Insulation does not stop air leaks—seal penetrations before blowing.
3. Compare installed cost
Blown-in needs rental machine or pro install; batts are DIY-friendly.
Blown-in vs fiberglass batt
Coverage quality beats nominal R-value on the label.
- Blown-in: Fewer gaps; faster retrofit; settles slightly over time.
- Fiberglass batt: Lower material cost; must fit without compression.
Use our calculators
Common mistakes
- Blocking soffit vents
- Compressing batts to fit
FAQ
Can I mix types?
Yes in layers—avoid double vapor barriers; follow manufacturer guidance.