Common Air Leak: The Chimney Chase

Has anyone ever told you that you have a leaky chimney? Most homes with a chimney extending into their attic do and this is a conversation I often have with homeowners.

Because fire code requires a gap between the framing of the attic floor and the chimney, most homes have a significant air leak for most of their life. If a gap of this size was located around your front door, you would undoubtedly feel a draft and know that there is something wrong.

This common air leak often goes undetected because in the winter, the warm air rises through this gap. What most people don't realize is that as that warm air rises and dissipates, it pulls cold air from the outside into the house, typically through leaks and cracks around the basement and foundation walls. Because these leaks and cracks are not concentrated as one large crack, it becomes difficult to pinpoint where the problem is.

One sign of a chimney air leak is staining of sheetrock around the chimney on the upper levels. Usually assumed to be a roof leak, these are often the result of your warm air leaving through this gap and condensing on the flashing around the chimney at the roof. The condensed moisture then drips off the flashing, staining the sheetrock.

While code requires there to be a gap between the flammable attic floor and the brick of the chimney, code does allow for non-flammable material, such as Roxul, steel and fire-rated caulking, to bridge that gap. By using a combination of these and other materials, we are able to seal the gap and install a fire-rated barrier higher up the chimney in the event cellulose is blown in to further insulate the attic.