to make the measurement process easier anderson has created the measurement guide for Anderson would write double-hung insert windows this guide is available online and provides measurement instructions in 5 easy steps the first step is to take accurate measurements of the existing windows the goal is to determine the size of the existing window frame in order to specify the proper insert replacement window unit measure the width of each window from the inside
surface of the side jam to the inside surface of the opposite side jam if jam liners are present it may be necessary to remove them to measure from wood surface to wood surface take this measurement at three locations at the sill at the check rail and at the head the smallest of these three dimensions is the insert windows opening width record the measurement in the step 1 width column along with a detailed description
of the windows location on the measurement guide next take the vertical measurements measure from the top of the sill just behind the stool to the underside of the head jam again take this measurement at three locations once at each side jam and in the middle the smallest of these three dimensions will be used to determine the new insert windows height record the measurement in the step two height column on the measurement guide in step
three you must check that the existing window frame is square check this by measuring diagonally from corner to corner diagonal dimensions must be within one quarter inch if they're not it'll be necessary to determine how much smaller the replacement insert window must be to fit into the out of square opening if a window frame is so severely skewed...
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