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A homeowner’s question on GreenBuildingAdvisor describes cold air entering through a roughly 10-inch gap between a Brooklyn brownstone’s rear brick wall and flat-roof deck. The owner is planning to add polyiso insulation above the roof deck and asked how to air-seal the gap; the source does not include a confirmed repair or expert answer.
A Brooklyn brownstone owner has asked how to seal a drafty opening between the rear brick wall and the roof deck before adding insulation above a flat roof. The homeowner’s question, published by GreenBuildingAdvisor, describes a gap about the height of the roof joists—estimated at 10 inches—where cold air is entering despite an exterior fascia board.
The homeowner said the opening runs between the top of the rear brick wall and the underside of the roof deck. A fascia board covers the outside face of the wall, but, according to the post, it has not stopped cold air from passing through. The owner described the air as moving freely and asked how to air-seal or otherwise address the space.
The planned roof work is to install polyiso insulation above the deck. The owner also said they are considering an interior vapor-control layer, identified in the post as Intello, that would cover the ceiling and extend roughly a foot down the interior walls. These are plans described by the homeowner, not completed work.
The post presents possible approaches raised by others: fitting pieces of polyiso between the joists and sealing their edges with spray foam, or packing the gap with insulation. The supplied report does not establish which approach is appropriate for this specific roof, and it does not include a final recommendation or a confirmed repair.
Air Leaks Before Roof Insulation
The question concerns more than adding insulation. If air can move through the roof-wall junction, filling the area with insulation alone may not address the pathway described by the homeowner. The issue is how to manage the connection between the brick wall, joist space and roof deck as part of the planned roof upgrade.
For the owner, the sequencing and compatibility of the air-sealing work, roof insulation and interior vapor-control layer could affect how the assembly performs. The source provides no inspection findings or building plans, so it cannot establish the cause of the airflow or identify a suitable detail. That uncertainty matters: the gap’s size and location are reported by the homeowner, but the construction around it has not been independently assessed.
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The Planned Flat-Roof Work
The owner framed the question as one step in a broader effort to improve air sealing in a Brooklyn townhouse. The next planned project is insulation above the flat-roof deck, rather than a reported roof replacement already underway. The post gives no construction date for the building or detailed description of the roof layers.
In asking for advice, the homeowner relayed two suggestions they had encountered: cut polyiso pieces to fit between the joists and seal the edges with spray foam, or use packed insulation. The owner also mentioned a planned interior layer of Intello. These details document the options under consideration; they are not findings from a building assessment, nor does the supplied material say that any method has been selected.
“The cold air still just merrily whistles through.”
— Brooklyn brownstone owner, in a question published by GreenBuildingAdvisor
Roof Junction Details Still Unknown
The supplied source does not report an expert response, a chosen repair, or work completed at the property. It also does not provide photographs, measurements beyond the owner’s approximate 10-inch estimate, or details about the joists, roof deck, fascia connection and existing insulation.
It is not clear whether the opening is continuous along the wall, how air reaches it, or whether other parts of the roof assembly affect the decision. The post also does not say whether the planned Intello layer has been selected as part of a professionally reviewed design. Without those details, the reported suggestions remain possibilities raised in the discussion, not a verified solution for this brownstone.
Advice Before Roof Work Begins
The homeowner’s stated next step is to add polyiso insulation above the roof deck. The question seeks guidance on whether and how to close the gap before or as part of that work. The source does not give a schedule, identify a contractor, or say whether the owner received further replies.
Any update would need to clarify how the roof-wall junction is built and what sealing detail, if any, the owner chooses. Until that information is available, the project’s outcome and the performance of any proposed repair remain unconfirmed.
Key Questions
What is the homeowner trying to seal?
The reported opening is between the top of the rear brick wall and the bottom of the flat-roof deck, in the area occupied by the roof joists. The owner estimates its height at about 10 inches.
Why is the fascia board not enough?
The homeowner says the fascia board covers the outside face of the brick wall but that cold air still passes through. The source does not describe the assembly in enough detail to explain the airflow path.
What repair options are mentioned?
The post relays suggestions to fit polyiso pieces between joists and seal their edges with spray foam, or to pack the space with insulation. It does not confirm either approach as suitable for this roof.
Has the homeowner completed the work?
No completed repair is reported. The homeowner says adding polyiso above the roof deck is the next planned project and asks for advice on the gap.
What remains unknown?
The source does not include a site inspection, full roof details, a confirmed air-sealing plan, or an expert recommendation. It also does not say whether the planned interior Intello layer will be installed.
Source: greenbuildingadvisor.com
