particular opening and it is important to correctly measure the opening. There are three critical measurements involved:
The width is the first measurement given when ordering a window. The width is measured from jamb to jamb because the
parting stop and inside trim are removed to install the new window. The top, middle and bottom of the opening should be
measured using the smallest of the three measurements. The windows will be manufactured 1/4 inch less to allow for 1/8
inch of play on either side to accommodate for out of square opening. The window might have to be ordered smaller in width
to compensate for out of square openings (See SQUARE measurement).
Second measurement. The height of the window is taken from the highest point of the sill against the stool, to the header (at
the point against the inside stop). Measure at the left, middle, and right using the smallest dimension. The windows will be
manufactured 1/4 inch less if it has no head expander or 3/4 inch less if it has a head expander to allow enough clearance
when placing the window into the opening over the stool.
This is the last measurement given. Measure the diagonals (upper left to lower right, and upper right to lower left) as accurately
as possible from a point inside the stool to a point against the inside stop at the header. Record the two dimensions. If the
meausurements are within 1/8 inch of each other, there should be no problem installing the window into the opening. If it is
more than 1/8 inch, then the window might have to be ordered smaller in WIDTH to compensate. Otherwise, it may cause the
new window to be forced into an out-of-square condition during installation.
Check the walls on both sides of the window opening using a level. If the wall is out of plumb, be prepared to make
adjustments when installing the window.
Check the sill with a level. Out-of-level sills may distort the frame and cause operation problems with the window.