One deep spot does not describe an uneven attic. Wet, compressed, displaced, mixed, or unknown material cannot be reduced to a trustworthy single depth estimate.
- ENERGY STAR estimates 2.5 R/in for loose fiberglass, 2.8 rock wool, 3.7 cellulose, 2.7 vermiculite/perlite, and 3.2 fiberglass batts.
- Record thin areas separately.
- Do not disturb vermiculite.
Formula or decision boundary
screening R estimate = representative depth in inches × official estimated R per inchScreening values from ENERGY STAR
| Material | Estimated R/in | Boundary |
|---|---|---|
| Loose fiberglass | 2.5 | settled depth |
| Rock wool | 2.8 | identified material |
| Cellulose | 3.7 | settled condition |
| Vermiculite/perlite | 2.7 | do not disturb suspected vermiculite |
| Fiberglass batts | 3.2 | uncompressed |
Use the answer
Screen hazards
Check safe access, wiring, fixtures, moisture, pests, and suspect material before entry.
Sample a pattern
Record multiple accessible depths and map low or disturbed areas.
Use the result as a screen
Compare with official zone guidance without claiming laboratory precision.
Safety and scope
- Do not disturb suspected vermiculite insulation.
- Use qualified help where access, wiring, combustion, or moisture conditions are unsafe.
Sources and scope
Source links reviewed July 16, 2026. A review date is not the document's publication date.
- ENERGY STAR: DIY Checks and InspectionsUnited States · government guide
Do not disturb suspected vermiculite insulation; obtain qualified guidance before work.
- Natural Resources Canada: Keeping the Heat In — Roofs and atticsCanada · government guide
Follow product labels for bag count and settled depth; do not disturb suspected vermiculite.