The first thing you will need to know is what the retailer wants for measurments.
FOR EXAMPLE ONLY!
In my area, for the brands that I used to sell, triple track, 2 glass & a screen with a flange on three sides and an expander at the bottom, this is what I did:
Now I am assuming that your 100 year old house has flat casings on the outside (1 X 5 box casings), if this is the case, this style of window is referd to as a "Eastern style" window in my area.
I would measure the width of the window opening between the inside of the 1 X 5, then measure the height from the top of the window sill to the edge of the 1 X 5 opening at the top.
Example, 27 1/2 X 53 Eastern (this tells them they have to add for the flange.)
Now you said you have 4 over 1 windows.Are you telling me that the meeting rail is not centerd in the frame and that the top sash is taller than the bottom sash?
If this is the case you have an oriel style window and you need to know how the company that is making them wants that measurement.
Note* If the top sash is much larger than the bottom sash, do not be surprised if you can't tilt the top sash of the storm in for cleaning. Most distributors have a cut sheet on how to measure for storm windows and how to determine what style you need.
Remember, once you have orderd them, they are yours. measure then check, then do it again!
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