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I've been installing replacement windows in my house and see the instructions to drill through the outer inside face of the trim to put screws laterally into the studs and sill and top header. The windows come with caps to cover the holes after the screws are put in. These windows come with nailing flange with holes every 4 or so inches and that's what I've used to secure the window. Before installing the windows I've added 2" of EPS foam-board insulation and on top of that 5/8 sheet of OSB. The nailing flange is screwed (4" screws) into the OSB (and finding the studs and sill). Is there a problem with not using lateral screws from inside the window trim to the studs? Seems cleaner not doing this, the window isin't going anywhere with all the nailing-flange screws. The lateral screws likely wouldn't hit wood - instead they'd likely hit the EPS insulation.

  • Can you include a few pictures of the windows? – JACK Aug 20 at 14:18
  • This is a product-related question and depends entirely on the manufacturer's specs. Andersen windows, for example, mount only by nailing flanges. You need to read your literature. – isherwood Aug 20 at 16:07
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You are probably correct that the nailing flange will hold the windows in place.

However, if there is ever a warranty claim, there's a very high likelihood that they'd deny it if you don't put the screws through face trim as they instruct. Heck, it's possible they'd try to deny the warranty because you've used screws (as I likely would) instead of nails through the nailing flange.

i.e. Failure to follow installation directions to the letter = failure to honor warranty.

Whether you choose to follow the instructions or take your chances on the warranty is your decision.

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  • Agreed, I'm a big screw fan, but nails through the nailing flanges seem to work best and introduce no unnecessary shear locally to the flange. I'd use ring shank nails maybe if you're worried about pop-out, but it's almost never an issue on nailing flanges if the nails are sized right and driven into healthy wood structure. – Unslander Monica Aug 21 at 19:14

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