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A Massachusetts homeowner is seeking a building-science review of a planned unvented attic assembly: 2 inches of closed-cell foam against the roof deck and 8 inches of open-cell foam beneath it. The supplied report records the homeowner’s concerns, but does not establish whether the design meets code or will prevent moisture problems.
A Massachusetts homeowner planning to convert a vented attic into an unvented roof assembly is questioning whether the proposed 2 inches of closed-cell foam beneath the roof deck, followed by 8 inches of open-cell foam, will meet code and limit moisture risk in climate Zone 5A. The supplied GreenBuildingAdvisor report presents the homeowner’s question, not a confirmed code ruling or a finding that the design is safe or unsafe.
The homeowner said the work was planned for a 1976 house in Massachusetts, with installation due to begin in early December. The existing attic is vented and has old fiberglass and cellulose insulation on the floor. An air handler and its ductwork are also in the attic, which the homeowner said was a main reason for choosing an unvented design. The house sustained interior water damage from ice dams the previous winter.
The contracted plan calls for removing the existing attic-floor insulation and applying 2 inches of closed-cell spray foam to the underside of the roof deck, then 8 inches of open-cell foam. The installer’s stated total is R-49. The homeowner said the rafters are less than 10 inches deep and the open-cell foam would extend beyond them without being trimmed. The plan also includes 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. Reading the cited IRC R806.5 provisions and Table R806.5, the homeowner understood that a hybrid assembly in Zone 5 needs at least R-20 of closed-cell insulation. They estimated that 2 inches provides about R-13 to R-15, and asked whether to request at least 3 inches or switch to all closed-cell foam, which they said would cost about $6,000 more. Those figures and the homeowner’s interpretation are reported as part of the question, not independently verified in the supplied material.
Code and Moisture Questions at the Roof
The proposed work affects more than insulation levels. Moving insulation from the attic floor to the roof deck changes the attic’s relationship to the house: the plan would make it an unvented attic and place the roof sheathing next to spray foam. That makes the assembly’s code compliance, control of moisture and ability to dry relevant to the durability of the roof as well as the home’s energy performance.
The homeowner’s report of prior ice-dam-related interior damage gives the decision added urgency, but the source does not establish what caused that damage or whether the planned foam system would prevent a recurrence. The attic’s air handler and ducts are part of the choice: keeping them inside the insulated enclosure may be a reason to consider a conditioned attic, while moisture control and construction details still need to be addressed. The report does not confirm that a small supply duct would solve the concern.
The financial choice is also material. The homeowner described all closed-cell foam as an alternative costing roughly $6,000 more than the contracted approach. Without a verified code review, project details and assessment of the roof assembly, that cost alone cannot show which option is appropriate.
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The Existing Attic and Proposed Change
The house has a hip roof with a new asphalt-shingle roof, ridge vent and soffit vents, according to the homeowner. It also has an old powered attic fan. The current attic is vented, with insulation on the attic floor; the project would remove that insulation and seal the soffits as part of converting the roofline to an unvented assembly.
The homeowner said a general contractor they consulted favored keeping the attic vented, sealing air leaks and installing blown cellulose on the floor instead. That would differ from the spray-foam proposal and would leave the air handler and ductwork in the attic. The question therefore concerns a choice between two different attic strategies, not simply an adjustment to foam thickness.
The homeowner also cited concerns they had read about damp roof sheathing beneath open-cell foam, particularly near ridges and on north-facing slopes. The supplied report does not provide measurements, an inspection, a response from the installer, or a building-science expert’s conclusion about this particular roof.
“The air handler and its ductwork are in the attic, which is one of the main reasons we went with an unvented attic.”
— The homeowner, in the GreenBuildingAdvisor question
Assembly Performance Still Unverified
The source does not say whether the work proceeded, whether local officials or a qualified building professional reviewed the assembly, or whether the cited code interpretation is correct for this project. It also does not establish the closed-cell foam’s actual R-value, the full roof and air-sealing details, or whether the installer’s stated R-49 total was independently checked.
There is no inspection or moisture data for the roof sheathing, and no expert response in the supplied material to the homeowner’s concern about dampness beneath open-cell foam. The proposed supply duct, the roof’s drying potential and the possible vented-attic alternative remain questions rather than resolved recommendations. The report also does not identify the year of the planned early-December installation.
Review Before Foam Installation
The next step described by the homeowner was the planned installation in early December; the supplied report does not provide an update on whether it went ahead. Before work begins, the homeowner’s questions point to issues for review: whether the exact assembly meets applicable local code, whether the specified closed-cell thickness is sufficient under that code, and how the design will manage moisture at the roof deck.
The homeowner also may need to decide whether to proceed with the proposed hybrid foam, seek a revised design or retain a vented attic with insulation on the floor. No choice or expert recommendation is documented in the source. A project-specific decision would need to account for the roof construction, attic equipment, ventilation and air-sealing details, rather than treating the reported R-value as a complete answer.
Key Questions
What insulation assembly did the homeowner plan to install?
The plan described in the report was 2 inches of closed-cell foam against the underside of the roof deck, with 8 inches of open-cell foam beneath it. The homeowner said the installer claimed a total of R-49.
Does the report confirm that the assembly meets Zone 5 code requirements?
No. The homeowner raised a question about how IRC R806.5 applies and estimated the closed-cell layer at R-13 to R-15, below the R-20 minimum they understood to apply. The supplied material contains no independent code determination.
Does 2 inches of closed-cell foam prevent moisture problems?
The report does not answer that question. It records concerns about damp sheathing under open-cell foam but provides no inspection findings, moisture measurements or expert assessment of this roof assembly.
What alternative did another contractor suggest?
The homeowner said a general contractor preferred keeping the attic vented, sealing air leaks and adding blown cellulose on the attic floor. The source does not compare that approach with the proposed unvented assembly or recommend one.
Did the planned installation take place?
The report says the homeowner expected work to start in early December, but it does not specify the year or say whether installation went ahead.
Source: greenbuildingadvisor.com
