Insulation Types & R-Value
~11 min read · Recognize insulation materials, expected R-values and installation defects that void them.
Insulation is judged by presence, coverage, and installation quality — not by reciting climate-zone R-tables that change every cycle. The inspector identifies the material, estimates depth, and hunts the gaps, compressions, and hazards that void the paper rating.
Materials and identification
The lineup: fiberglass batts and loose-fill (pink/yellow/white), cellulose (gray shredded paper, denser), mineral wool, spray foam — open-cell (soft, vapor-open) and closed-cell (rigid, vapor-closed), rigid foam boards, and the legacy set: vermiculite (pebbly granules — potential asbestos: DO NOT DISTURB, report for testing protocol) and old newspaper fill. Depth converts to approximate R-value by material (~R-3 to R-3.7 per inch for common loose products); the report gives material, average depth, and the estimate — coverage evenness matters more than the number.
- Identify material; estimate depth → approximate R
- Vermiculite: asbestos-suspect — hands off, report
- Evenness beats headline depth
Installation defects
R-value assumes perfect installation; the field never cooperates: gaps and voids (skipped bays, wind-scoured eaves), compression (batts crushed under storage flooring lose loft and value), misfitted batts (stuffed, folded, or bridging without contact), loose-fill drifted thin, kraft facing installed backwards or left exposed (the facing is flammable — cover requirement), and insulation missing at knee walls, skylight shafts, attic hatches (the uninsulated hatch is a chimney), and rim joists. Thermal bypasses — open chases, dropped soffits venting heat to the attic — defeat everything around them.
- Gaps, voids, compression, misfits: the value-killers
- Exposed kraft facing = flammability finding
- Hatches, knee walls, chases: the forgotten surfaces
Hazards and clearances
Insulation near heat: recessed lights need IC-rating to be covered (non-IC cans buried in insulation overheat — look for scorch and the rating label); keep clearance from flues and chimneys (combustibles-to-B-vent and masonry rules); attic vent blockage (soffits stuffed — the ventilation cross-reference); and K&T wiring buried under insulation (the electrical cross-reference). Wet insulation anywhere is a moisture finding first.
Worked example
An attic survey: 12 inches of even cellulose across most bays — but plywood storage platforms crush it to 3 inches over the master suite; two older recessed cans, unlabeled, sit buried with browned cellulose around their housings; the hatch is bare wood; and one corner holds a patch of pebbly gray-gold granules from a previous era. Build the report.
The good news first: ~12 inches of cellulose (≈R-40s) evenly blown — solid. The storage platform: compression to 3 inches drops that area to ~R-11 — a thermal hole over the most-used rooms; raised-platform or relocation recommendation. The buried cans: unlabeled + browned surrounding insulation = overheating evidence on possibly non-IC housings — fire-safety finding: verify IC rating or clear/replace. The bare hatch: an uninsulated door in the thermal boundary — weatherstrip and insulate. The granules: vermiculite — asbestos-suspect; do not disturb, note location, recommend testing per protocol before any attic work (this finding changes every future project's cost). Presence was fine; installation and legacy were the report.
Common exam pitfalls
Reporting R-value tables as the standard.
Zone requirements shift by cycle — report material, depth, evenness, and defects; frame improvements as efficiency upgrades.
Touching or sampling vermiculite.
Asbestos-suspect material is a do-not-disturb finding with a testing referral — full stop.
Missing the buried non-IC can.
Scorched insulation around recessed lights is a fire finding — verify IC labels before blessing buried cans.
Name it, gauge it, mind the gaps — and pebbly gold granules mean stop touching and start writing.
Recap
- Identify material; depth → approximate R; evenness rules
- Compression, voids, misfits erase rated value
- Exposed kraft facing is flammable
- IC-rating check on buried cans; flue clearances
- Vermiculite: asbestos-suspect, do not disturb
- Cross-reference ventilation, wiring, moisture
Prove it: 10 questions on this topic
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