To Fin Or Not To Fin

To fin or not to fin that is the question. Those may not be the exact words of Shakespeare but they are a question that he would be asking if he were replacing his windows. Here is an excerpt from the American Architectural Manufactures Association (AAMA) Installation Masters manual.

When removal of the entire existing mounting flange window is required, the installer should exercise caution to avoid damaging any of the existing building materials during the removal process. The recommended method of removal is to expose the mounting flange, pull the anchors, and remove the window intact. Collapsing the frame of a mounting flange window is not recommended and should be avoided.

Wenatchee Valley Glass believes that the nail fin is an integral part of a window that provides not only structure to the window frame it also helps the window attain its performance rating.   When a window is tested by AAMA it is installed as it would be in new construction with the nail flange and associated flashings and sealants.   You want to get the performance that you are paying for out of your windows don’t you.    We do!   That is why whenever possible we cut back the siding on your house, expose the nail fin, remove the window completely, and cut back the window liners to accommodate the increased frame depth of a new vinyl window.    Your new window is installed with caulking behind the nailing fin and the exterior is trimmed out with a trim of your choice.   We can even drop off the trim prior to installation so you can apply a coat of paint before it is installed.

What are the pitfalls with installing a window without a flange?

  1. You are removing part of the structure if the window.   The nailing flange acts as a structural I-beam that helps prevent the window frame from warping.
  2. The fin is a additional weather barrier.   If the window is installed without a flange you are relying solely on caulking to keep out the wind and rain.    The window may be caulked beautifully but wind can enter through cracks in the siding and travel underneath the caulking and into your house.
  3. Windows without the support of nail fins don’t operate as well over time.    Quite often as a labor savings method the interior window liners are not cut back when installing a flangeless window.  This leads to the new window sticking out beyond where it was intended by the manufacturer leaving the exterior of the window unsupported.

Does Wenatchee Valley Glass install windows without nail fins?  The answer is yes in limited situations.   Whenever possible we do however try to use the fin.   After all it is how we would want the windows installed in our house so why wouldn’t we do yours the same way!