Rough Opening - Aluminum Window

I have recently replaced all the old wooden windows in my home with stock size alum windows. That project went "relatively" well, even though this old house is hardly plumb, square, and level anymore...
Now, I need to cut & frame a new hole for a new 2/8 3/0 window. Question is this, what is the typical rough opening for that size, or perhaps a more general question would be how much bigger should the hole be than the actual window itself - excluding the nail fins?
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BiloxiBoy wrote:

It's roughly 2"-2 1/2" So I usually will make it 2 1/4" not per side but overall.
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Evo wrote:

If the rough opening is 2.25" larger than the window unit the nails through the flanges will hit air. Andersen, for example, uses a rough opening size that's 1/2" larger than the unit size.
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Thanks for the replies. I ended up making the opening 5/8 inch bigger on each side and top and bottom. Worked out okay, but getting a window to sit right in an old house with old frameing and "aged" 3/4 pine plank siding can be a real pain. All's well that ends well though. Thanks again...
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