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).

3 Answers 3


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:


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.

  • 2
    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
    Commented Dec 17, 2012 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
    Commented Dec 17, 2012 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
    Commented Dec 17, 2012 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
    Commented Dec 17, 2012 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
    Commented Dec 17, 2012 at 16:58

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.

  • 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. Commented Dec 17, 2012 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
    Commented Dec 17, 2012 at 16:08

Using silicone behind a vinyl window flange (flanges constructed as part of the window frame, not tapped on) will not only void most warranties but also have the potential to break the window in temperature changes. Vinyl expands and contracts in hot and cold weather. This is why many high quality siding panels have a thermometer taped onto each panel with the appropriate position to nail. This is why Azek vinyl decking seams will look perfectly tight in one temperature and open up in another, only to find their way back to the tightened position the next morning. This is also why many window flange nail holes are oblong shaped and not circular, to allow room for expansion. Waterproofing comes from the outside prep not hidden under it.

  • When I've seen window manufacturers specify a bead of something on the back of the nail flange, they specify "elastomeric latex" or "sealant." The word silicone does not appear because silicone has negative interactions with Tyvek. The point of putting the sealant under the window flange is to compress the house wrap against the sheathing, blocking air flow between the wrap and sheathing. Commented Jun 24, 2016 at 4:16

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