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A Massachusetts homeowner asked whether a proposed unvented attic retrofit—2 inches of closed-cell foam beneath 8 inches of open-cell foam—would adequately manage moisture in climate zone 5A. The supplied report describes the homeowner’s concerns but does not provide an expert answer or confirm that the work proceeded.
A Massachusetts homeowner planning an unvented attic retrofit asked whether 2 inches of closed-cell foam beneath 8 inches of open-cell foam would control moisture at the roof deck in climate zone 5A. The account, published as a question on GreenBuildingAdvisor, describes the proposed work and the homeowner’s code and condensation concerns but does not include a final expert assessment.
The homeowner said the 1976 house had experienced interior water damage from ice dams the previous winter. Its asphalt-shingle roof was described as new, with ridge and soffit vents, while the attic remained vented and had old fiberglass and cellulose insulation on the floor. An air handler and ductwork are located in the attic, a reason the homeowner gave for considering an unvented design.
The contractor’s proposed assembly was to remove the existing attic-floor insulation and install 2 inches of closed-cell spray foam directly against the underside of the roof deck, followed by 8 inches of open-cell foam. The contractor reportedly claimed the assembly would provide R-49. The plan also called for sealing the soffits, extending the bathroom-fan vent through the foam and applying an ignition-barrier coating. The foam would extend past rafters less than 10 inches deep and, according to the homeowner, would not be trimmed.
The homeowner questioned whether the closed-cell layer met the requirements they had read in IRC R806.5 and Table R806.5. They estimated that 2 inches of closed-cell foam would provide about R-13 to R-15 and asked whether more thickness, all closed-cell foam or a different attic design would be appropriate. The source records that question; it does not verify the applicable code interpretation or establish that the proposed assembly is compliant.
Moisture Control at the Roof Deck
The decision affects more than the insulation rating. In an unvented attic, the roof assembly’s ability to limit air movement and manage moisture can affect the condition of the sheathing, particularly during cold weather. The homeowner said an insurance estimator had raised concerns about moisture accumulation and had read reports of damp sheathing beneath open-cell foam near ridges and on north-facing slopes. Those are concerns reported by the homeowner, not findings confirmed for this house.
The attic also contains heating and cooling equipment and ducts. Moving insulation from the attic floor to the roofline changes the boundary between indoor and outdoor conditions, so the details of air sealing, ventilation strategy and equipment operation matter alongside the nominal R-value. The supplied account does not include a building-science inspection, moisture measurements or a determination that the proposed foam combination will prevent condensation.
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A Retrofit After Ice-Dam Damage
The homeowner linked the planned retrofit to ice-dam-related interior damage from the prior winter. Ice dams can be associated with heat loss and snowmelt at a roof, but the source does not identify the cause of this home’s damage or say that insulation alone would resolve it. The roof was described as having ridge and soffit vents, and the existing attic was vented before the proposed conversion.
A general contractor consulted by the homeowner reportedly favored keeping the attic vented, air-sealing the ceiling and adding blown cellulose at the attic floor. The homeowner questioned that option because the air handler and ductwork are in the attic and the roof is a hip design. The source does not compare bids, provide a project-specific design or establish which approach is preferable.
““The contracted plan” calls for “2″ of closed-cell foam directly on the underside of the roof deck, then 8″ of open cell under it.””
— The homeowner, as quoted in the GreenBuildingAdvisor question
Code and Assembly Questions Remain
The source does not resolve whether 2 inches of closed-cell foam satisfies the applicable code provisions for this specific assembly, or whether the stated R-value and foam thicknesses were independently checked. Requirements can depend on the adopted code edition and the details of the design; the homeowner’s reading of a code table is not a confirmed ruling by a building official.
It is also unclear whether the installer assessed the roof deck, indoor humidity, air leakage, foam product specifications or the risks at the ridge and north-facing slopes. The account does not say whether the soffit and ridge vents would be fully disabled as part of the conversion, how the attic would receive conditioning air, or whether a return-air path was included. The homeowner asked about adding a supply duct but did not report a decision.
The report does not state whether the work began in early December, whether a permit or inspection was obtained, or what happened to the old powered attic fan. It provides no post-installation measurements or evidence that the proposed design did or did not prevent moisture problems.
Verify the Design Before Installation
The next step described in the source was the homeowner’s planned installation in early December, but no year or subsequent project update is provided. Before work proceeds, the homeowner’s outstanding questions include the required closed-cell thickness, whether the hybrid design is appropriate for the roof and climate, and how the attic will be conditioned and inspected.
The source does not report a final recommendation. The outcome would depend on project-specific details and review of the adopted code requirements, rather than on the stated R-value alone.
Key Questions
What insulation assembly was proposed?
The homeowner said the contractor planned 2 inches of closed-cell foam against the roof deck with 8 inches of open-cell foam beneath it, for a contractor-reported R-49. The source does not independently verify that rating.
Does the source confirm that 2 inches of closed-cell foam meets Zone 5 code requirements?
No. The homeowner cited IRC R806.5 and Table R806.5 and estimated the foam’s R-value, but the report does not include a code official’s determination or an expert answer for this assembly.
Was moisture damage found under the proposed foam?
No such finding is reported. The homeowner described concern about possible damp sheathing based on an insurance estimator’s warning and material they had read, but the source gives no inspection results for this roof.
What alternative did the homeowner consider?
A general contractor reportedly favored retaining a vented attic, air-sealing the ceiling and adding blown cellulose to the attic floor. The homeowner raised the attic ductwork and hip-roof layout as factors in weighing that option.
Source: greenbuildingadvisor.com
