An Anderson Township cathedral ceiling: unvented hot-roof retrofit with closed-cell foam

The starting point

A 1992 hillside home in Anderson Township, 2,800 sqft, with an architecturally prominent cathedral living room ceiling spanning roughly 28 feet long by 18 feet wide at peak (about 500 sqft of cathedral surface area). Original construction: 2x10 rafter cavities filled with R-19 fiberglass batts, with a 1-inch ventilation channel above the batts and ridge-and-soffit venting per code-minimum 1992 design.

The owners had been in the home since 2001 and reported two recurring problems:

1. Ice damming every winter. The cathedral roof melted snow faster than the rest of the home's roofline because of warmer ceiling-side temperatures. Snowmelt refroze at the eave, building ice dams that lifted shingles and let water back into the soffit. 2. Condensation streaks every summer. Visible vertical streaks on the cathedral ceiling drywall around the edges. Mold testing during a 2018 inspection had been negative but the streaking was getting worse year-over-year.

Both problems traced to the same root cause: inadequate insulation and air seal in the cathedral assembly.

Why "unvented hot-roof" was the right answer

The cathedral assembly's original design relied on continuous soffit-to-ridge ventilation to keep the underside of the roof deck cold. After 30 years, the ventilation was no longer continuous. The soffit baffles had been crushed during 2008 attic-storage shuffling. Insulation had settled into the ventilation channel in two spots. The system was a "compromised vented assembly" which is worse than either a properly-vented or properly-unvented design.

Two paths forward:

Path A: restore the vented assembly. Pull all the existing fiberglass, replace soffit baffles, install new insulation tight to the bottom of the rafters, restore the 1-inch ventilation channel, replace the soffit and ridge vents. Cost roughly $7,500-$11,000. Restores original design but does not improve thermal performance much.

Path B: convert to unvented hot-roof. Pull all the existing fiberglass. Install closed-cell foam directly to the underside of the roof deck (no ventilation channel). The closed-cell foam acts as both insulation and vapor retarder. The roof deck stays at conditioned-space temperature. No ice dams, no condensation.

The owners picked Path B. Quote: $9,200 fixed.

The install (2 days)

Day 1: Crew of 3 removed all existing fiberglass batts. Cleaned debris from the rafter bays. Removed the soffit and ridge vents (no longer needed). Patched the soffit and ridge openings. Verified no leaks during a hose test.

Day 2: Truck-mounted spray rig set up in the driveway. Closed-cell foam applied to the underside of the roof deck in 2-inch lifts, 3 lifts total (6-inch final depth, R-42 nominal). Total spray time: 4 hours.

The verification

Pre-install thermal imaging (during a 14°F outdoor evening): cathedral ceiling surface temperature averaged 44°F, with visible cold spots near the rafters dropping to 38°F. Indoor wall temperature elsewhere: 65-67°F.

Post-install thermal imaging (during a comparable 16°F evening): cathedral ceiling surface temperature averaged 65°F, matching the rest of the room. No visible cold spots anywhere.

Post-install winter performance: zero ice damming for the first winter. Zero condensation streaks for the first summer.

What about snow load and roof structure?

A common concern with unvented hot-roof retrofits: when the roof deck stays warm in winter, snow that lands on the roof melts faster than on a cold-deck design, and the meltwater runs off rather than accumulating. In Cincinnati climate (Climate Zone 4A, modest snow loads), this is generally a benefit (less snow weight on the structure) rather than a problem.

The shingle manufacturer warranty: most current asphalt shingles allow unvented hot-roof installation per IRC R806.5 with appropriate insulation R-value above the roof deck or vapor retarder configuration. The lead technician confirmed the homeowner's GAF Timberline shingles were warranty-compatible with the unvented assembly.

What this case shows for Cincinnati cathedral-ceiling homeowners

If your home has a cathedral ceiling and any of:

• Visible ice dams every winter
• Condensation streaks on the ceiling
• Drafty cold ceiling temperatures during winter
• A 30+ year-old original vented assembly with unknown ventilation integrity

The unvented hot-roof retrofit is generally the right path. Cost: $7,500-$15,000 for typical Cincinnati cathedral footprints. The federal Section 25C insulation credit ended December 31, 2025; ask your CPA about Ohio state programs and Duke Energy or CenterPoint Energy utility rebates that may apply in 2026.

Things to confirm with the local installer:

1. Closed-cell foam at proper depth for Climate Zone 4. Minimum R-49 in attic per Energy Star recommendations, achievable with 7+ inches of closed-cell. 2. Existing fiberglass complete removal. Leaving fiberglass below new foam creates a moisture-trap risk. 3. Soffit and ridge vent capping. Permanent closure of the existing vents. 4. Manufacturer warranty compatibility on shingles. Verify before signing.