Garage Construction Project

2026-07-01 - Call - Midstate Spray Foam R-49 and Flash-and-Batt Guidance

3 min read

Purpose

Follow-up call with Eli Coblentz (Midstate) on the R-49 question raised while reviewing the full-roof foam quote: does the quoted 5½” closed cell meet Clare County code, and if not, is it better to add foam or do flash-and-batt?

Weather

N/A — phone call.

Notes

Clare County only requires the 5½” (≈ R-38) — not a hard R-49

  • Eli: because this is a cathedral / roof-plane assembly (his words, roughly “the roof is above the walls” — the ceiling follows the roof, no attic above it), Clare County accepts the reduced value and requires only the quoted 5½” of closed cell.
  • He contrasted this with Traverse City, which enforces a hard R-49. Jurisdiction-dependent interpretation — this maps to the IRC R402.2.2 depth-limited “ceilings without attic space” exception (the Clare permit packet shows R-49 as the prescriptive baseline; the exception is what Clare applies and Traverse City doesn’t).
  • Eli’s opinion: the extra foam to reach R-49 is likely not worth the upfront cost for the marginal energy gain.
  • ⚠️ This is the installer’s account of the local inspector’s practice (he permits in Clare regularly) — high-confidence, but still worth a direct confirmation from the Clare County building official for the record.

Strongly advises AGAINST flash-and-batt — condensation failures

  • Midstate used to install flash-and-batt and deliberately stopped. Eli’s reasoning: warm interior air migrates through the air-permeable batt, reaches the cold face of the closed-cell foam, and condenses — trapping moisture in that space.
  • Several of their flash-and-batt installs failed after a few years from exactly this. They now steer clear entirely.
  • If the owner “has to have” R-49, Eli strongly recommends adding more foam, not batt.
  • Building-science note for the file: this is the classic under-flashed condensation mode, worst with thin (1–2”) flash. A 5½” flash (R-38 ≈ 78% of a R-49 assembly) keeps the foam face well above dew point per the R806.5 ratio and is more forgiving in theory — but given Midstate’s real field failures and eave-pinch imperfections, the practical call lands the same: all-foam over flash-and-batt.

Pricing — thicker foam = lower $/board-foot

  • Confirmed he buys 55-gallon drums and runs a professional heated sprayer (as predicted — the reason pro beats DIY kits; see Insulation Strategy DIY cost analysis).
  • 1.75/board-foot” vs. the ~$0.96/bd-ft implied at 5½”.
  • Implication: the incremental cost to add foam (5½” → ~7”) is cheaper than a linear estimate — the rig is already set up and paid for.

Decisions

  • None finalized. Leaning toward accepting the 5½” quote as-is — code-compliant in Clare per Eli, and the extra R-value isn’t worth the cost. Flash-and-batt is off the table on the installer’s failure experience. If R-49 margin is still wanted, add foam (not batt). Pending direct building-official confirmation.

Action Items

  • Confirm with the Clare County building official that 5½” (≈R-38) satisfies code for this cathedral assembly (R402.2.2 depth-limited exception) — for the record — owner:: Owner — stage:: 5
  • If pursuing R-49 anyway, ask Eli for the incremental price to build foam to ~7” (not flash-and-batt) — owner:: Owner — stage:: 5

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