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Is using 2" roofing nails on the nailing fins of new construction windows enough to hold them in place permanently? It seems to me like there should be some fasteners in the extension jambs, but maybe I'm just remembering back to when I installed some replacement windows (without nailing fins).

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Matthew PK offers some very specific instructions. I happen to disagree with most of them, but they may work for some windows. I will simply state that every new window comes with specific installation instructions. You should follow them. Otherwise you will void the manufacturer's warranty.

Here is an informative article from Fine Homebuilding:

http://www.finehomebuilding.com/how-to/install-replacement-windows-and-flashing-correctly.aspx

As far as fastening the jamb extensions to the trimmer stud goes - unless the window installation instructions specifically forbid it you may want to shim and trim screw just to guarantee plumb/square. The casing is typically what connects the jamb extension to the trimmer studs.

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Which points do you disagree with? I find that your linked article instructs exactly as I did, except they use nails instead of screws. –  Matthew Dec 17 '12 at 16:03
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First point, silicone may work for some window and flashing combinations, but not all. Solvent interactions with vinyl windows, bitumen, etc. should be appropriate to the specific window and flashing system. Screws are essentially worthless in this situation, as they afford less shear value and can damage the flange far more easily than nails. Lastly, there are any number of windows where simply nailing the fins is sufficient. Provided you follow other instructions as well. –  Paul Dec 17 '12 at 16:09
    
I improperly used the term "silicone" to describe weathertight caulking. Fair enough. I'd still use screws instead of nails, they just require more care when being driven (as do nearly all uses of screws). I suppose the OP asked if nails were sufficient to hold the window in place, and they are sufficient to hold it in place but my point was that they are not sufficient for a correct install. –  Matthew Dec 17 '12 at 16:27
    
Agreed. It was my impression that he was inquiring about structural durability of the window install, and not about the proper way to flash/waterproof a window. I'm willing to concede the applicability of screws in a window installation if you specifically state "pan-head screws with an appropriate shear value." –  Paul Dec 17 '12 at 16:36
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As I said in my post, if you're using jamb extensions the casing will provide a strong mechanical attachment to your framing. There are a number of window installs where no jamb extensions are used or provided, and in those cases the only mechanical connection of window to frame is through the nailing flange. To reiterate, if you follow the installation instructions your window will have been installed correctly. –  Paul Dec 17 '12 at 16:58
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You should apply silicone in a thick bead under the flange, including under each fastener penetration. Some people choose not to apply silicone to the bottom lip of the flange.

You should screw through every other flange hole. Wipe silicone over the top of the fastener.

Finally, once the silicone is dry, you should apply flashing tape to the sides, then the top of the window. Some people choose to flash the framed opening as well, before mounting the window.

So, to answer your question: no, simply nailing the fins is insufficient.

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Well it's too late to add any screws to the nailing fins since I'm all nailed up and flashed. The install instructions for the windows didn't say anything about screws in the nailing fins, but they also didn't say anything about screws in the extension jambs. At this point the extension jambs are my only option and I'm just trying to figure out if that's necessary. –  milkboneUnderwear Dec 17 '12 at 15:56
    
@milkboneUnderwear while I can relate to your predicament, next time it might be prudent to ask the question before you do the work ;-) –  Matthew Dec 17 '12 at 16:08
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