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A Massachusetts homeowner asked GreenBuildingAdvisor readers whether a proposed hybrid spray-foam assembly is suitable for a Zone 5A attic after ice dams caused interior water damage. The source is a homeowner’s question, not a reported inspection or expert ruling; it does not establish that the proposed 2-inch closed-cell layer meets code or will prevent moisture problems.
A Massachusetts homeowner planning to replace attic insulation before an early December installation asked whether a roof-deck assembly of 2 inches of closed-cell foam under 8 inches of open-cell foam would be adequate in climate Zone 5A. The homeowner’s account, published as a question on GreenBuildingAdvisor, describes previous ice-dam damage and concerns about code requirements and moisture; it does not provide an expert verdict on the proposed work.
The homeowner said the 1976 house had interior water damage from ice dams the previous winter. The roof had since been replaced with asphalt shingles and includes a ridge vent and soffit vents. The attic is currently vented and has old fiberglass and cellulose on the floor, as well as an older powered roof fan. The homeowner said an air handler and ductwork are located in the attic and were a key reason for considering an unvented design.
Under the contractor’s proposed plan, the existing attic-floor insulation would be removed and not replaced. The underside of the roof deck would receive 2 inches of closed-cell foam, followed by 8 inches of open-cell foam, for a stated total of R-49. The homeowner said the rafters are less than 10 inches deep, so the open-cell foam would extend beyond them and would not be trimmed. The plan also calls for sealing the soffits, extending a bathroom-fan vent through the foam and applying an ignition-barrier coating.
The homeowner questioned whether the closed-cell layer is thick enough under the cited IRC R806.5 provisions. In the post, the homeowner interpreted the code table as requiring at least R-20 of closed-cell foam for this type of hybrid assembly in Zone 5, and estimated that 2 inches provides about R-13 to R-15. That interpretation and those R-values are reported as the homeowner’s concern; the source does not include a code official’s review, product specifications or an assessment of the planned installation.
Code and Moisture Questions for the Roof
The proposed work would move insulation from the attic floor to the roof deck, changing the attic from a vented space to an intended unvented attic. That matters because the air handler and ducts would sit within the insulated enclosure, while the roof assembly would need to manage air leakage and moisture without relying on the existing attic ventilation path.
The homeowner’s question points to two separate issues that should not be treated as settled by the stated R-49 total. One is whether the specific closed-cell layer satisfies the applicable code pathway for a hybrid assembly. The other is whether the completed roof deck will remain sufficiently dry under actual indoor humidity, weather and installation conditions. A concern about damp sheathing is not proof that this assembly will fail, but the post does not establish that the proposed thickness prevents that risk either.
The choice also has a practical cost and design dimension: the homeowner said switching to all closed-cell foam would cost about $6,000 more, while a contractor favored keeping the attic vented and insulating the floor. Those options involve different approaches to the attic’s ducts, ventilation and roof assembly. The source offers no bids, energy analysis or professional comparison that would determine which option is best for this house.
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From Ice-Dam Repairs to Attic Redesign
The homeowner is considering the insulation work after ice-dam-related interior damage, but the question does not establish what caused the ice dams or whether the new roof addressed their underlying conditions. The account identifies Massachusetts as the location and Zone 5A as the climate classification supplied by the homeowner.
The proposed roof-deck approach is intended to bring the attic and its mechanical equipment inside the home’s insulated boundary. A separate contractor, according to the homeowner, preferred retaining a vented attic, air-sealing the ceiling and installing blown cellulose on the attic floor. The post raises these approaches as competing options; it does not report that either has been selected after a code review or building-science assessment.
“2″ of closed-cell foam directly on the underside of the roof deck, then 8″ of open cell under it, for a claimed R-49.”
— The homeowner, in the GreenBuildingAdvisor question
Key Details Still Need Verification
The source is a homeowner’s request for feedback, not a completed project report. It does not say whether the insulation work went ahead, whether the contractor changed the specification, or what advice readers or professionals ultimately gave. The planned early December date is not tied to a year.
It is also unclear whether 2 inches of the specified closed-cell product would deliver the R-value the homeowner estimates, or whether the proposed assembly meets the applicable code requirements in the jurisdiction. Product data, local code interpretation and any required approvals are not included. The post also gives no measurements of indoor humidity, roof-deck moisture, air leakage or ventilation performance that would resolve the homeowner’s concern about damp sheathing.
Other details that could affect evaluation—including the roof’s full assembly, the exact foam products, installation quality, the design of the bathroom-fan exhaust termination, and how the attic air handler receives suitable air—are not documented in the source. The stated concerns about moisture near ridges and on north-facing slopes are the homeowner’s reported reading, not evidence that this particular roof has those conditions.
Review Before Foam Installation
The immediate next step described by the homeowner was to seek a “gut check” before the contractor began work in early December. The source does not report a final decision. Before proceeding, the homeowner would need to resolve the cited code question with the local building department or a qualified building professional and confirm the specified foam products’ tested properties and installation details.
A project review could also compare the proposed unvented roof assembly with the vented-attic option, taking account of the attic ductwork, roof design and previous ice-dam damage. Whether to add supply air or another approach to controlling attic conditions remains an open question in the post, not an established requirement or solution. Any later report on the work, inspection, or moisture monitoring would be needed to show what was ultimately installed and how it performed.
Key Questions
What insulation assembly was proposed?
The homeowner said the contractor planned to apply 2 inches of closed-cell foam against the roof deck and 8 inches of open-cell foam beneath it, for a claimed R-49. The source does not independently verify that rating.
Does the source confirm that the plan meets Zone 5 code requirements?
No. The homeowner interpreted IRC R806.5 and Table R806.5 as requiring at least R-20 of closed-cell foam in this hybrid assembly. The post includes no ruling by a local code official or other independent confirmation.
Is the proposed foam assembly proven to prevent roof-deck moisture?
No such finding appears in the source. The homeowner raised concerns about moisture under open-cell foam, but the post provides no measurements, inspection findings or expert assessment of this roof.
What alternative was under consideration?
The homeowner said another contractor favored keeping the attic vented, air-sealing the attic floor and adding blown cellulose there. The source does not report a final comparison or decision.
Was the insulation work completed?
The post says installation was planned for early December, but gives no year and does not report whether the work took place or what the final design was.
Source: greenbuildingadvisor.com
