One of the easiest tasks in a construction project is to install a window in an opening that has been freshly framed. A nailing fin is a feature that most new construction casements include. These can be found on aluminum or vinyl-clad windows. The nailing fin can be either made of vinyl or metal. It has approximately 1 1/2 inches in width and nails holes every 4 to 6 inches.
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Brick molding can still be found on primed wood windows, but nailing fins replace it. These fins not only make it easier to install but also provide a better seal against air and water infiltration. These windows can be flashed, but are not required. Flashing or a drip edge may be required for windows that do not have a porch roof or soffit above them.
Before installing a window, ensure that the sheathing does not hang into the opening. This will reduce the size of your opening so that the window can fit into it. After measuring the opening, make sure it is large enough to accommodate the window. It is not a good idea to try to fit a heavy window into an opening.
Rough openings are typically 1" wider than the window unit and 2 1/2" taller. The manufacturer will provide a rough opening specification. Also, make sure that the window works properly. Double hangs should be able to slide up and down and casements should open and close easily.