I've removed 7 old windows and installing 7 new ones exact size.
I would be best way to install window to ensure there's no outside draft getting through?
Normally I just install window and of course foam core is on the house......then squirk that expandable spray installation between window and frame.
There is also a waterproof, draft-proof "tape" you can install on the exterior flanges, if you have exterior flanges.
Then you've no flanges on that type of window.
Draft is a lot less an issue than that WATER stuff.
Given that these are holes into your house and into the wall, you might wanna have a pro come in and work with you on it.
Flashing and insulation depend on exposure and your geography.
(said the guy dealing with replacing some sliding doors because the builder flashed it just fine for a house that doesn't get hard winds coming up a hill and blowing water UP. Then I get to fix/replace some floors).
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