Originally Posted by jogr
You kinda got the cart in front of the horse.
Is this a new construction window or a replacement window? By that I don't mean is this new construction or not - I mean what type of window did you buy? Does it have nail flanges, or was it meant to use the existing window jamb? Tell us exactly what window you bought (manufacturer and model).
If new construction window what is the current rough opening of your window and how did you determine it? What is the RO requirement for the new window?
What kind of siding do you have around the window? What kind of millwork and sill do you have on the inside?
Sorry, replacement window. It comes with it's own hardware for mounting so no it doesn't use the existing jamb. It's brick/block all the way around.