Flush-Fin, Block-Fit, & New Construction Windows & Doors

Which installation method is right for you?

Flush-fin, block-fit, and new construction are different application for installing windows and doors.  To determine which method is best for you and your home it is important to understand the fundamentals of each of these applications.

The Flush-fin Installation

Just to get this out of the way, the flush-fin application has many different industry and proprietary names.  Here is a list of the more common names that Clear Concepts Window & Door uses.

  • Flush Fin (Generic) 
  • Stucco Fin (Generic)
  • Single Wall Flush Fin (PlyGem)
  • Dual Wall Flush Fin (PlyGem)
  • Retro-fit Fin (Generic)
  • Retro-fit Flange (Generic)
  • Bullnose Fin (Simonton)
  • Craftsman Fin (Simonton)
  • Brickmold Fin (Simonton)
  • Z-Bar (Milgard)

retro_fit_installationRegardless of the name, the installation method is the same.  The new vinyl, fiberglass, or aluminum flush-fin window is installed on top of the existing window’s perimeter frame.  Integral flush-fins are extruded (vinyl/aluminum) or pultruded (fiberglass) with the main frame of the new window; creating a seamless application.  The flush-fin installation is utilized when the perimeter frame of the existing window frame is not pulled out of the opening.  By not pulling the existing perimeter frame, all original flashing and counter-flashing (nail-fin) is preserved; maintaining the vapor barrier of the home.  Assuming there isn’t any water or structural damage to opening, a flush-fin application is the most ideal installation method. It alleviates the need to involve any exterior or interior wall demolition and/or repair.  If your home has existing aluminum or steel windows and doors, the flush-fin application is the most economical installation method.  Demolition of the existing aluminum or steel windows and doors includes removal of the operable and fixed sashes, and inter-lock rail.
 Again, the perimeter frame is not removed and the new flush-fin window is installed on top of and inside the existing perimeter frame. Some refer to this as the “jump frame” method.  The new window is fastened using stainless steel, self-tapping screws.  The screws are fastened perpendicular to the jamb, penetrating the new window frame, drywall, and stud framing members.  The screw is covered with a plug to hide the screw head.  Insulating foam is applied around the window frame and flat trim is applied, concealing the old perimeter frame and giving a beautiful seamless finish.  Typically a houseful of windows and doors can be installed in just one day.

The Block-Fit Installation

The block-fit installation method is most commonly applied to homes that have existing wood windows, particularly double-hung or casement wood windows.  Unlike flush-fin or nail-fin windows, the block-fit window does not have a fin at all.  An existing wood window perimeter frame does not utilize the “jump frame” installation method.  
Rather, the block-fit window is installed into a “pocket” of the existing wood window frame. Demolition of the existing wood window includes removal of the interior stop, removal of operable and fixed sashes, and removal of the intermediate stop. The new block-fit window is inserted into the pocket and sealed against the exterior wood stop using a high-grade polyurethane. The screws are fastened perpendicular to the jamb, penetrating the new window frame, drywall/plaster, and stud framing members.  Depending on the manufacturer and design of the new window, plugs to cover the screw heads may or may not be applied due to limited clearance of the vertically sliding sashes. The existing interior wood stop is then reapplied with finish nails and finished with paintable acrylic caulking.  Some touch-up paint may be required.  

The Nail-Fin Installation

The nail-fin installation method is utilized when the home’s framing members need to be or are already exposed.  This installation method is traditionally used when the home or room addition is first being constructed. During this process, the framing members of the wall are exposed and flashing methods are being observed and applied to create the vapor barrier of the home.  The nail-fin of a window or door works in conjunction with the flashing paper around the opening.  The nail-fin acts as counter-flashing., the nail-fin, flashing paper, and building paper are integrated together to protect the home from water infiltration. A nail-fin application is also utilized when a home owner would like to alter the dimensions of an opening; moving framing members to make the dimensions of the opening bigger or smaller.  If there is water or structural damage to the opening, a nail-fin application will also be required.  If the existing flashing around the window opening has failed, then new flashing will need to be applied.  The exterior wall will need to be opened up, flashing removed, and new flashing applied.  Depending on the extent of damage, the immediate framing members may need to be replaced as well.  When utilizing the nail-fin application, screws or nails are fastend through the nail-fin and into the framing member or stud wall.  stucco_demo_window_installation_afterPolyurethane is applied on the back of the nail-fin before installed into the opening.  This is known as “back-beading.”  An additional bead of polyurethane is applied on top of the nail-fin after the fasteners of been installed; ensuring a water-tight seal.  All nail-fin, polyurethane, flashing, and fasteners are covered when the exterior wall’s stucco or siding is applied. 

So Which Method is Right for You?

If you are feeling overwhelmed right about now, it’s okay.  That’s why we are here to help!  Our 23 years of experience and expertise will help you to make the right decision.  One of our professional team members will be happy to come out to your home and provide a free assessment and evaluation.  At Clear Concepts Window & Door, we take the time to educate each of our clients.  We provide a thorough inspection of all of your windows and doors and offer our expert opinion. We’ll handle the “nuts and bolts” of the decision-making.  And, you can focus on the more important details like which color frames to choose, rain or glue chip privacy glass, and most importantly; what will you do with all that money you are saving now that you have new energy efficient windows and doors!


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