Difference Between New Windows and Replacement Windows


When choosing windows for your home, you will likely have to choose between two main types of windows: new construction windows or replacement windows. Except in a few isolated instances, these two types of windows are mutually exclusive. Read on to discover what distinguishes new windows and replacement windows.

What is the difference between new windows and replacement windows? New construction windows feature nailing or attachment fins, or flanges, which are found on the exterior side of the window. On the contrary, replacement windows don’t have nail fins or flanges – they have smooth sides to allow for easy insertion. New construction windows are fitted into clear openings in the house, whereas replacement windows replace existing new construction or replacement windows. You will find new construction windows being used in new structures or for deep remodeling, while replacement windows are used when a structure has a peripheral area that is in good shape. Unlike with new construction windows, you may run into problems with replacement windows over time due to weather elements as they don’t have the protection that nail fins provide for their counterparts.

New windows, or new construction windows as they’re known in the window industry, are different from replacement windows in several ways. Read on to discover more about these types of windows, including when to use each of them.

What is a replacement window?

Replacement windows are made for easy installation into already existing window openings. Some terms that you might come across used in relation to replacement windows include:

1. Retrofit windows

Replacement windows are sometimes known as retrofit windows. Replacement windows are fitted into pre-existing openings with little to no disturbance to the structure.

2. Flush fin windows

These are typically used for installation in homes that have stucco exteriors (they can also be used on other home exteriors but are most commonly associated with stucco). They are sometimes referred to as flange windows, jump frame windows, or z-bar windows. Flush fin windows bear a similarity to insert windows and fit within an existing window frame. The exterior fin is designed to extend far enough to conceal the existing frame. 

3. Block frame windows

These include the window’s mainframe (top header, left and right jambs, lower rail) as well as all the operational parts of the window (glass, sash, and hardware). They bear a close resemblance to new construction windows except that they lack a nail fin around the perimeter. Block frame windows are commonly used in full window replacements.

4. Insert window replacement

This is a window installation process that involves fitting a fully assembled window within an existing frame (try to picture a secondary frame within an existing frame). Insert windows are sometimes referred to as pocket windows and are typically installed within original solid wood window frames, but only if the frame is still in good condition.

5. Full frame window replacement

This is a window installation process that involves fully removing the existing window, frame, moldings, and jambs, down to the original studs (down to the rough opening for the window). It’s often believed that only new construction windows can be used for full-frame window installations, but block frame windows can also be used for these projects as they are also fitted into a rough opening.

6. Sash kits

These are used in window replacement projects. Sash replacement kits are typically installed on an existing window frame to give it jamb liners and sashes.

What is a new construction window?

New construction windows are made for new homes or home additions. Unlike their counterparts, new construction windows are installed on the framing directly, when the sheathing or studs are still exposed. The design of a new construction window features a nail fin which is simply a center flange around the perimeter of the window frame. This nail fin is used to fasten the window into place and enhances waterproofing.

What is the difference between replacement and new construction windows?

The main distinguishing factors between these types of windows are as follows:

  • In new construction window installation projects, you can frame openings based on the windows you plan to install but in replacement applications, you work with pre-existing openings.
  • New-construction windows have a nailing or attachment fin, or a flange which are located on the exterior side of the window. The nail fin is placed against the frame opening and nailed flat or screwed to the framing. This provides an additional protective layer against air and water infiltration. Replacement windows on the other hand have no flanges or nailing fins, featuring smooth sides to allow for easy insertion instead.
  • New construction windows are used when building new structures, for deep remodeling projects, or for repairing severely damaged existing structures. Replacement windows are used in structures that have an existing window and the peripheral area that is in good condition.
  • New construction windows are completely weather-tight when properly installed. Replacement window technicians need to add weatherproofing properties because replacement windows lack the protection that nail fins provide for their counterparts.

When to use new-construction windows

1. When building a new house

When you’re building a new house, you will need new construction windows. There is no need to install replacement windows since there are no windows are being replaced. All new homes will typically use new construction windows.

2. For remodels

New-construction windows can be used in a variety of remodeling scenarios:

3. When creating a new opening

If you intend to create a new window opening in an existing wall or an addition, it will need to be framed. Go for a window with a nail fin that attaches to the exposed studs.

4. When converting a door to a window

If your project involves converting a door opening to a window opening, you will need new framing to create the appropriate size opening for the new window. New framing means that the studs will be exposed so that new construction windows can be installed. 

5. When expanding an opening

If your project involves installing a window that is bigger or smaller than the existing opening allows, the installation team will need to reframe the wall cavity to install the new window. Go for a window that features a nail fin so that it can be completely attached to the new studs.

6. When building an addition

An addition can be defined as a smaller version of a new house. Unless you have a very peculiar situation on your hands, you will almost always install a new construction window with additions. The only time you may want to steer clear of a new construction window is when you intend to incorporate a portion of an existing wall into your addition.

7. When you need to replace a window that is in extremely bad shape

When you have a window that is in bad shape, the peripheral area is likely in also bad shape. The framing around the window, as well as the exterior siding, interior drywall, wall studs, and sometimes even the floor covering and subflooring may have compromised by rot, carpenter ants, or termites.

Because extensive carpentry work will be required, it will be just as easy and cost-effective to install a new construction window as it is to put in a replacement window. A new construction window will provide better insulation from the variable weather conditions than a replacement window. Because of the nail fins, it will be more weatherproof than its counterpart.

When to use replacement windows

1. When you need to replace an existing window

Installing a new construction window in an opening that is in good condition, you’ll end up creating more damage than if you choose to install a replacement window instead. Window, trim, wall, and siding elements are all connected – when you modify one element, you modify other elements. 

Replacement windows usually do require some minimal temporary modifications, such as the removal of interior trim. Nonetheless, as long as the trim isn’t damaged as it’s removed, it can usually be replaced.

2. If your wood window frames are still in good condition

If you have old wood windows that haven’t had any leaking issues and the frames are still in good working condition, consider choosing insert windows. When the wood frame is still in good condition, you can install a new window unit within that frame but it does reduce the amount of visible glass surface.

3. When using new construction windows that feature detachable fins

In some cases, you may be able to modify your new construction windows and turn them into replacement windows. Some designs of new construction windows have fins that can be snapped or cut off.

Can you use new construction windows for replacement?

New construction windows can be used for replacement projects. If your project involves replacing a window and you have to remove the wall’s exterior siding down to the studs of the wall, you may want to consider a new construction window with a nail fin. If your replacement project doesn’t expose the wall’s framing, you can remove the nail fins from the windows so that you don’t have to reorder windows without the fin.

Are new construction windows cheaper than replacement windows?

New construction windows can be more cost-effective to install than replacement windows, but the cost will ultimately depend on the quality and quantity of windows you use. Your project costs will likely increase if you have an existing home and intend to do a remodel or addition using windows that have nail fins. Renovations using existing window openings are usually cheaper because less labor is needed.

Final thoughts

When it’s all said and done, there are only two types of windows to choose from – the replacement and new construction. It’s important to be sure of what you want to go for so that you get your money’s worth. Both have specific advantages designed for different installation methods, so you want to do your research before making a purchase.

Melanie Asiba

Melanie is an author. She enjoys traveling, reading and trying out new things. In addition to writing for Apartment ABC. Connect with her at [email protected]

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