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Does my flat roof have to be vented if the annular space is completely filled with insulation?

GBA Editor | Posted in General Questions on

I live in a 1880’s Brooklyn brick row house with a flat roof (17 x 40). While there are two existing roof vents I was wondering if they could be removed if the flat roof’s annular space is completely filled with insulation. Last fall I blew in cellulose insulation in the back portion of the house filling most of the area but not filling in around the back roof vent – I could still see some light when I looked through the cut I made in my ceiling.

I had not gotten around to doing the front section until now – and I’m wondering if I should completely blow insulation for both the larger front space – (Roof is slightly pitched here so there’s more annular space!) and completely fill up the entire roof – removing any air gaps / pockets etc. and ultimately the roof vents.

Should I assume with a completely filled space there are no moisture issues. But with a partially filled space there would be and thus the need for roof vents. Over time wouldn’t the “completely filled” cellulose settle creating air pockets that might create moisture transfer problems?

Any guidance would be greatly appreciated!


  1. GBA Editor
    Martin Holladay | | #1

    Your roof will be fine without ventilation. Just pay attention to interior air barrier details at the ceiling.

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