Window installation instruction
You will often hear contractors and manufacturers use the terms New Construction or Replacement (Retrofit) when discussing residential windows. While neither window must be used exclusively for the project after which they're named, each has specific advantages designed for these different installation methods.
New Construction Window
New construction windows typically have a nail fin. When homes are built, the framing is likely constructed of wood studs. The nail fin rests against the outside of the stud, and nails, staples or screws are driven through the holes in the fin. All other exterior materials are then applied and butted up to the frame of the window or trim.