Window installation method - Nailing fin

Nailing fins, often referred to as mounting flanges, are the slender strips positioned on the exterior facets of a window. Unlike a "front flange," which serves as a decorative trim element, a nailing fin is typically recessed from the outer boundary of the window frame and features fastener holes punctured within it. The primary function of nailing fins is to firmly secure the window to the wall sheathing and maintain its stability while shims and screws are being affixed. Moreover, fins collaborate with flashing and the weather-resistant barrier (WRB) to effectively prevent intrusion by wind and water, thereby enhancing the overall integrity and performance of the window installation.

1.  Applications of Nailing Fin Installation

European window manufacturers often design their products based on local installation practices, which differ significantly from American installation methods. Consequently, European windows are also designed differently from American windows. While few people in Europe are familiar with windows with nailing fins, they are very popular in the United States.

2.  Which windows are not suitable for nailing fins?

Replacement windows, sometimes called “inserts,” don’t have nailing fins because they are typically installed with the existing cladding still on the wall, which means there is no exposed sheathing for them to be fastened to. Replacement windows are fastened through the window frames into the sides of the window openings. Commercial windows are often installed into block or steel rough openings where a nailing fin would be impractical.

3.  The two types of window nailing fins

Windows are commonly equipped with two types of nailing fins: integral and non-integral.

The term "integral" for nailing fins originates from the fact that the nailing fin and window frame are extruded as a single, solid unit. During window assembly, all four corners are melted and fused together, forming a sealed shell that encircles the window's entire perimeter. This design feature is exclusively present in vinyl windows.

4.  How to install with integral and non-integral nailing fins

In the course of assembly, non-integral nailing fins are attached to window frames crafted from wood, metal, and fiberglass. It is imperative that the areas where the fins converge at the corners, as well as the seams between the fins and frames, be properly sealed during the installation of the windows. Employing non-integral nailing fins offers several distinct advantages. Their ability to be folded down renders them more resilient against damage during both storage and transportation. Additionally, the folding feature facilitates the ease of pushing a window through a rough opening from the interior, eliminating the necessity of carrying it up a ladder or scaffolding – a trait of utmost significance, particularly when installing large windows on higher stories.

The rigidity of integral fins compels a window to adhere strictly to the plane of the sheathing, even in instances where the wall is significantly twisted or deviates from plumb. This rigidity can lead to misalignment of weather strips, impede smooth operation, and impose stress on the glass, potentially causing seals to deteriorate prematurely. In contrast, the flexibility of non-integral fins offers enhanced adjustability during installation and acts as a cushion when the house settles, mitigating such issues.