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A Brooklyn brownstone homeowner described cold air moving through a gap between the rear brick wall and flat-roof deck, and asked how to seal it before installing polyiso insulation above the deck. The source is a homeowner’s question, not a report of completed work or a published expert recommendation; the best repair and its results remain unknown.
A Brooklyn brownstone homeowner has asked how to air-seal a gap beneath a flat roof before adding polyiso insulation above the roof deck, describing cold air moving between the rear brick wall and the underside of the deck. The GreenBuildingAdvisor post records the homeowner’s question and proposed options, but does not include an expert answer, a confirmed repair plan or a result.
The homeowner said the gap runs from the top of the rear brick wall to the bottom of the roof deck and is approximately the height of a roof joist, estimated in the post at 10 inches. A fascia board covers the opening from outside, but the owner reported that cold air still passes through. The account does not describe an inspection or provide measurements beyond that estimate.
The planned roof work is to install polyiso insulation above the flat-roof deck. The homeowner asked whether to cut pieces of polyiso to fit between joists and seal them with spray foam, or to pack the space with insulation. These are options raised in the question, not recommendations confirmed by a building professional.
The post also says the owners plan to install an Intello vapor-control membrane over the ceiling and extend it around the top foot or so of the interior walls. The supplied source does not explain how that planned interior work would connect to the roof-edge gap, nor whether the proposed sequence or materials have been reviewed for this particular building.
Roof-Edge Airflow Before Insulation
The question highlights a practical concern for owners planning roof insulation: air leakage at the roof edge may need attention alongside insulation. The homeowner’s report of cold air passing behind the fascia makes the opening a specific point to investigate before the roof assembly is changed. The source, however, does not establish how much heat is being lost or identify the exact route of the airflow.
The answer matters because the proposed work involves an existing flat-roof assembly and several materials intended to control heat, air and moisture. Choosing between fitting rigid insulation, using spray foam or adding other insulation cannot be settled from the post alone. The best approach may depend on what is actually behind the fascia, the condition of the roof and wall junction, and how the new layers are designed to work together.
No energy savings, comfort improvement, cost, code finding or completed repair is reported. Readers should treat the post as a question about a building detail, not evidence that any one method has been tested or shown to work in this brownstone.
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The Planned Flat-Roof Work
The homeowner framed the gap as the next issue in a broader effort to tighten the brownstone’s air sealing. The planned project is to add insulation above the existing roof deck, while a separate interior plan calls for a membrane over the ceiling and partway down the inside walls. The post does not provide drawings, photographs, roof-layer details or information about the building’s construction history.
The question was published on GreenBuildingAdvisor, a building-advice site, and invited suggestions from readers. The source material supplied here contains only the homeowner’s description and questions. It does not include replies from site contributors, a professional assessment, or documentation that work has begun. That distinction limits what can be reported about the repair itself.
“The cold air still just merrily whistles through.”
— Brooklyn homeowner, in a GreenBuildingAdvisor question
Repair Method and Roof Details
The source does not confirm what is causing the airflow, whether the gap is continuous along the wall, or whether the fascia conceals additional openings. It gives no inspection findings, photographs, drawings or detailed roof assembly description. The homeowner’s estimate of the gap’s height is not presented as a measured dimension.
It is also unknown whether the suggested polyiso blocks, spray foam or packed insulation would be suitable for this specific junction. No professional has been quoted, and the post does not establish how the roof insulation, air-control layer and planned interior membrane would meet. There is no reported repair, cost, schedule, permit review or measured outcome.
Awaiting Advice or an Inspection
The next confirmed step in the source is not a construction milestone: the homeowner is seeking advice on how to address the gap as part of planned roof work. The supplied report does not say whether a response was posted or whether the owners have selected a method. Any update on the project’s timing, final design or performance remains unavailable.
Before work proceeds, the opening and roof-wall connection would need to be assessed in the context of the full assembly. For work affecting a roof or building envelope, owners should consult a qualified building professional familiar with local requirements rather than treating suggestions in an unanswered forum question as a specification. The source does not report that such an assessment has taken place.
Key Questions
What gap did the Brooklyn homeowner describe?
The homeowner described a gap between the top of the rear brick wall and the underside of the roof deck, estimated to be about the height of a roof joist, or roughly 10 inches. The post does not give a verified measurement.
What work is planned for the roof?
The homeowner said the next project is to add polyiso insulation above the flat-roof deck. The post does not confirm a start date or that the work has begun.
Did the source recommend spray foam or insulation?
No. The homeowner mentioned cutting polyiso pieces and sealing them with spray foam, as well as packing the gap with insulation, as ideas they had encountered. The supplied source contains no expert answer or confirmed recommendation.
Has the air leak been repaired?
The source does not report a repair or a result. It documents a question about cold air passing behind the fascia and asks how to seal the opening.
Source: greenbuildingadvisor.com
