Which Window Replacement is Right For My Project?

Which Window Replacement is Right For My Project? It Depends . . .

When our estimators or installers look at a project, we are able to tell a customer the best window replacement method or methods based on their situation. In certain situations there maybe more than one option available. I have tried to summarize the different methods for replacing a window along with common terminology.

There are a couple of window replacement methods common to the industry.  These include Block Frame, Z Bar(or Replacement Flange), and New Construction (or Nail on Flange).  While the previously listed types of replacements all yield the result of a new window, there are some distinct differences that are important for owner’s to understand.  Not all types of replacement window installations will fit every project.   Most window and door manufacturers offer a solution to answer all type of installation but some of the higher end products (wood clad windows) cannot be installed using the Zbar or replacement flange method due to the waterproofing and jamb details for wood windows.


Marvin New Construction or Nail On Window Photo Taken During Installation

Block Frame

A Block Frame window replacement is normally where the original wood perimeter frame is left in place and a new window comprised of either new jambliners and sashes or a complete frame unit with a jamb are installed.  The normal frame thickness on a insert window for a block frame is a jamb depth of 3 1/4″.  Older homes including Victorians, Bungalows, and wood windows with masonry surrounds are usually candidates for block frame window replacement.  One critical element for block frame replacement is the condition of the existing wood jambs and sill. The existing frame section must be in good shape to make sure that the new window can be properly fitted and installed into the opening.  The existing frame should not have it’s installation compromised in any way.  In the event the existing frame is damaged or rotted a new nail on installation should be considered.


Interior Photo of Marvin Clad Tilt Pac Window Installed by Old Town Glass in Petaluma, CA

The photo above shows the interior installation of Marvin Tilt Pac, insert windows being used to replace the original wood sash windows on a project in Petaluma, CA.  The Tilt Pac is comprised of a new set of vinyl jamb liners with balance hardware and two new double pane aluminum clad exterior, wood interior sashes.

The photo below shows a commercial and residential building in San Francisco, prior to the installation of Milgard White Vinyl Block Frame, Sloped Sill Tuscany Replacement Windows.  The Tuscany features a 3 1/4″ jamb that allows the window to easily installed into old double hung frame that have a 3 1/4″ sash opening.



This photo shows installation of Marvin Clad Ultimate Insert “Replacement” Double Hung windows in a commercial project in Petaluma, CA in Kentucky Street.  The aluminum clad exterior was chosen to match the original green exterior of the windows.  The Marvin insert worked well in this application since the existing building is a brick facade.  The original window frame were in excellent shape but the original wood sashes were completely rotted and the glass was falling out.  By installing a Marvin Clad Ultimate Insert Double Hung into this particular opening the owner got a exterior to satisfy historical requirements in the downtown historic district and a maintenance free exterior.  The interior of the windows shipped from the factory with a primed interior for finish painting in the field.

BEFORE: Original Wood Double Hung Window with Wood Sashes Prior to Installation of a Marvin Clad Ultimate Insert Double Hung
AFTER: Two Marvin Clad Ultimate Insert Double Hung Windows with Hampton Sage Exterior and Primed Wood Interior. Installed in a Historic Building in Petaluma, Ca with a Brick Exterior Facade

Z Bar or Replacement Flange

Zbar’s or Replacement windows are made by most manufacturers of vinyl or fiberglass windows.  The zbar flange comes from the shape of the window.  It is “Z” shaped and it has a large exterior flange that is designed to fit over the existing aluminum window’s perimeter frame that it is going over the top of.  The flange is wider on the exterior to conceal the existing frame and create a transition between old a new.

A replacement window is best used in a stucco or masonry application. Zbar’s can be used in wood siding application but this is done on a case by case basis and may require modifications to the windows prior to installation.  Milgard Window and Doors has an excellent video on replacing windows with vinyl zbars. Check it out below.

One thing to note is that a replacement or z bar is not recommend if you have water damage and/or know that there is a flashing or installation failure between old existing aluminum frame window or have dry rot.  When an old aluminum frame window is replaced with a zbar or replacement flange window, the existing perimeter remains untouched.  All the glass and interior frame sections are removed then the new window is replaced over the top of it.  It is sealed in place with a high quality polyurethane sealant.  The interior is finished with a vinyl trim that conceals the original old aluminum frame from view and provide a clean finish.  A bead of latex caulking then finishes the interior joints between the existing sheet rock and new vinyl trim.

Nail on Flange or New Construction

A nail on window, commonly referred to as a new construction window is what is installed into new commercial or residential structures when they are built from the ground up.  The term comes from the nail on flange that is attached to the side of the window to allow it to be nailed off to a building’s structure.  The nail on flange is used to fasten and flash/waterproof the new windows to the structure.  The photo below shows a Marvin Clad Ultimate Casement window with brick mold casing and a aluminum nail on flange during installation.  The beige aluminum flange and black butyl corner are used to fasten and waterproof the new window to the building.  The white flashing paper with the green writing is the window flashing that the new window sits against.  The flashing helps provide a weather barrier between the new window and the building’s wood framed structure.


Nail on windows can be used in replacement construction, too.  When you have an old window that is no longer functional, leaks, and/or a building that requires complete replacement of the fenestration assembly – the situation calls for a nail on window.   Nail on windows (or new construction windows) can be installed in any type of structure. These include wood frame, with stucco, wood siding, masonry etc.  A nail on installation is usually simplest in a project with some form of wood or composite siding due to these materials allowing for the easiest reintegration of the finish after the window or door is installed.

However, stucco is relatively simple it just requires a bit more finish work in order to blend where a window or door has been replaced with the existing finish coat.  The photo below shows an old single pane aluminum window before and after it has been replaced with Marvin aluminum clad casement window after installation.  The after photo is shown after the finish stucco work but before a final coat of paint.  In the after photo, you can see area around the window that is highlighted by a slightly different color.  This is the area or original stucco that was removed in order for the existing window to be removed and a new window to be installed.  The amount of area is large in order for the new windows nail on flange to be flashed and waterproofed to the existing structure.

BEFORE: Single Pane Aluminum Window, Prior to Replacement with a New Marvin Clad Ultimate Casement Window
AFTER: Marvin Clad Ultimate Casement Pair After Installation in a Stucco Application


Marvin Clad Ultimate Sliding French Door Installed to Replace a Single Pane Aluminum Door in a Home in Tiburon, CA with Wood Siding

If you have windows and doors that have dry rot or a structure with a comprised weather resistant barrier then a nail on is definitely the best replacement method. If your existing window and doors look like the photos below, you are  looking at a full frame replacement.

Wood Exterior Door in Wood Siding with Significant Dry Rot

With new construction or nail on window installation, the installers have many options for wateproofing and flashing.  These include peel and stick flashing such as Grace Vycor Pro, a butyl based product or a liquid membrane system such as Prosoco’s Fast Flash shown below.

Fleetwood Aluminum Nail On Door and Window Installation with Fast Flash From Prosoco, Inc.

We recommend you contact a window and door professional if you require assistance with the method for your window replacement.  If you are in the Northern San Francisco Bay Area, please give us a call.  Old Town Glass based in Novato, CA is a licensed California Contractor with installers trained to the AAMA Installation Master’s level.



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