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Community and Q&A

How to seal a Bilco door to prevent heat loss and moist air transfer?

Jas Thurber | Posted in GBA Pro Help on

We have a standard exterior Bilco door that leads to semi-finished space in our basement. We are having trouble with cold air coming in during the winter months and damp air in the spring/summer months. How can we seal this Bilco door without creating condensation issues around the door and/or seal? The air is coming from the cracks at the door hinges and around the doors themselves. It appears that the Bilco casing unit is sealed properly to the concrete. Home Depot sells polycarbonate domes that cover the doors. I considered putting a line of weather stripping along the bottom edges of a dome to create a seal of sorts for the dome to use during the summer months, but don’t know if that would solve the problem. I am assuming the dome will do nothing to help in the winter. I considered putting a piece of rigid foam board at the base of the Bilco stairs leading into the basement, as there is a doorway frame made out of 2x4s at the base. However, I am wondering if I would run into condensation issues on the Bilco door side? I also don’t love XPS board. I know that it off-gasses and our basement also has finished space where the kids play. I do have a roll of Dennyfoil vapor barrier that I could wrap the XPS board with I suppose. The basement room that the Bilco opens to is insulated with standard batt fiberglass (but no sheet rock). It is framed off from the mechanical room (also insulated, with no sheet rock) and finished space. There is a standard door that leads to the finished space from the Bilco room. Any suggestions would be greatly appreciated. Thanks!

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  1. Dan Kolbert | | #1

    You'll have a much easier time building your own insulated door at the foundation wall.

  2. GBA Editor
    Martin Holladay | | #2

    Dan is correct. The air sealing occurs at the door installed at the base of the stairs rather than at the steel bulkhead door.

  3. The Bilco Company | | #3

    This is the correct answer. Bilco recommends the use of an insulated vertical door at the bottom of the stairs for both energy efficiency and added security. Outdoor metal surfaces will always get extremely hot and cool basement air on the underside will generate condensation. Bilco brand doors are designed to be weathertight but are intentionally designed with air gaps on the underside. This equalizes the temperature on both sides of the metal doors to eliminate condensation.

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