Replacement vs. New-Construction Windows: Similarities and Differences

When buying windows for your home, you are confronted with two types of windows: replacement windows and new-construction windows. Do you need to make a choice between the windows? Where would you use replacement windows vs. new-construction windows?

When to Use Replacement vs. New-Construction Windows

The similarity between replacement windows and new-construction windows is that both types of windows give the homeowner the same post-installation result: a weathertight, operable or fixed sealed glass window unit.

New-construction and replacement windows are mutually exclusive. New-construction windows are used when you are extensively remodeling a wall and have access to the studs or when you are building a new wall. Replacement windows are used when the wall system stays in place and just the existing window needs replacement.

New-Construction Windows vs. Replacement Windows

Type of Window

New-Construction Windows: New-construction windows are meant for clear openings in the house usually with no trim or siding in place. New-construction windows have nailing or attachment fins, or flanges, on the exterior side of the window. Some new-construction windows have detachable nailing flanges.

Replacement Windows: Replacement windows replace existing new-construction or replacement windows. Replacement windows have no nailing fins or flanges. They are smooth-sided for easy insertion.

Availability

New-Construction Windows: New-construction windows are easily available and in stock at most home centers, though the range of sizes is limited.

Replacement Windows: Replacement windows are difficult for do-it-yourselfers to obtain, though there are a number of online sources for replacement windows. Even so, ordering and installing replacement windows is not a common DIY project.

Where to Use

New-Construction Windows: Use new-construction windows when building new structures, deep remodeling, or for repairing badly damaged existing structures.

Replacement Windows: Use replacement windows when the structure has an existing window and the peripheral area is in good shape.

Cross-Over Potential

New-Construction Windows: The only time you may need to use new-construction windows in a replacement window situation is when the wall and frame are badly deteriorated. In this case, the wall needs to be extensively rebuilt.

Replacement Windows: Rarely, if ever, is there a need to use a replacement window in a new-construction situation. New-construction windows are a better product to use in a new wall system.

Performance

New-Construction Windows: New-construction windows are weather-tight when installed correctly. The IGU, or insulated glass unit, is the same as the replacement window's IGU.

Replacement Windows: Replacement windows are weather-tight, as well, though the absence of the nailing fins is not a positive feature.

Do-It-Yourself

New-Construction Windows: New-construction windows are moderately easy to install (though much of the peripheral work is difficult). The presence of new-construction windows in home centers means that these windows are frequently installed by homeowners in sheds, outbuildings, ADUs, or in new wall systems in the primary structure.

Replacement Windows: Replacement windows can be tricky for do-it-yourselfers to install due to exacting tolerances.

When to Use New-Construction Windows

Generally, use new-construction windows when the wall system is being originally constructed or when it is being substantially rebuilt. You'll also want to use new-construction windows for:

• New house
• Addition
• ADU or outbuilding
• Severely damaged wall that needs much repair work
• Wall is being substantially rebuilt for any reason

Building a New House

Building a new house is the perfect example of new construction; thus, the need for new-construction windows. There is never a need to use replacement windows since no windows are being replaced. All new homes use new-construction windows.

Building an Addition

An addition is a smaller version of a new house. Unless you are dealing with a very unusual circumstance, you will almost always use a new-construction window with additions. The only time you may not want to use a new-construction window is when you are incorporating a portion of an existing wall into your addition.

Replacing an Extremely Damaged Window

When the window is in bad shape, it almost always follows that the peripheral area is in bad shape. The framing around the window, exterior siding, interior drywall, wall studs, and even floor covering and subflooring may have been compromised by termites, rot, or carpenter ants. Even if it is just a matter of removing the exterior window trim, new-construction windows are still the better option.

Because you will need to perform extensive carpentry work, it will be just as simple, easy, and cheap to install a new-construction window as it is to put in a replacement window. A new-construction window will be more substantial and will provide better insulation from the elements than a replacement window. Because of the attached nailing fins, it will be more weather-tight than replacement windows.

When to Use Replacement Windows

Generally, use replacement windows when the wall has already been built and cannot be disturbed in any major way (other than removing the existing window and replacing interior trim and exterior casing). Replacement windows are best for:

• One-for-one replacement of an existing window
• New-construction window with nailing fins that are designed to be detached
• Wall must stay in place as much as possible

Replacing an Existing Window

Installing a new-construction window in a good wall will create more damage and work for you than installing a replacement window. Window, wall, trim, and siding elements are all connected; when you alter one element, you alter other elements.

The great value in using replacement windows is that they are designed to slide in horizontally while replacing a minimum of other elements. Usually, replacement windows do require some minimal, temporary alterations, such as the removal of interior trim. However, as long as the trim is carefully removed, it can usually be replaced on a one-for-one basis. Some painting is usually required after the trim has been replaced.

Using New-Construction Windows With Detachable Fins

If new-construction windows have molded fins and replacement windows do not, does it stand to reason that you can remove the attached fins on the former and turn them into the latter? While this is not common, in a few cases it is possible.

Some brands of new-construction windows have fins that are designed to be snapped or cut off. This provides the greatest possible utility to these windows.

Generally, it is not advisable to cut off molded fins from new-construction windows that do not have purposely detachable fins. You may compromise the window's structure or break the glass in the sash while cutting. Also, it can be difficult to smooth down the outer edges of the window enough for the window to tightly slide into place and remain weather-tight.