How to Install a Window Without Nailing Fins

Nailing fins are flanges on the outside of vinyl and aluminum windows that sit flush agains the sheathing when the window is in place. They provide a convenient way to attach the window, but wood windows, as well as some aluminum and vinyl ones, don't have these fins. When the fins are absent, you have to drive fasteners through the window frame and into the building framing. It isn't difficult to get good results, provided that you prepare the window rough opening, making sure it's the right size, and level the window before you attach it.


Measure the dimensions of the window with a tape measure and frame the rough opening to be 1/2 inch wider and 1/2 inch longer. The window should fit comfortably without binding, and there should be enough room to adjust its orientation.


Seal the sill with tarpaper or with a vinyl sill sealer. It should extend for the full length of the sill and be wide enough to bend over the edges of the sill plate. Staple the sealer to the sill plate.


Close the window you are going to install. If it has a removable sash, remove it. Lift the frame into the opening and center it in the middle of the sill plate. You may need help to do this.


Place a level on the bottom of the frame and tap cedar shims under the frame with a hammer to center the bubble. When you're finished, place the level along the vertical side of the frame and adjust the top of the frame to center the bubble. Tap a shim between the top of the frame and the header to hold the window in place.


Tap shims into the gap between the frame and the vertical studs on both sides of the window. Put two shims in each side and space them roughly equal distances from the top and bottom of the window.


Drill a 1/8-inch hole through the window frame and into the building framing in front of each shim along the sides of the window. Don't drill holes in the top or bottom of the window.


Drive a 2 1/2-inch screw into each hole, but leave it loose. After you've driven a screw into each of the four holes, fine-tune the shims between the bottom of the window and the sill to make sure the window opens and closes properly. Finish tightening the screws, making sure they aren't tight enough to draw the sides of the window outward.


Cut all the shims flush to the window frame with a handsaw. Install wood trim to hide the gaps between the window and the framing and give the window a finished appearance.