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Community and Q&A

Installing vinyl windows

Jim Wright | Posted in General Questions on

I’m at the point of installing new construction vinyl windows in my house and I am uncertain about two aspects of the installation.

1) Caulk behind the window fins; yes on no ?

The manufacturer says yes, but in an article on, it states that it is “unnecessary and dumb”.

With proper flashing, it does seem kind of redundant; sort of like wearing a belt with suspenders.

What say ye ?

2) Nail the fins tight or nail loose like vinyl siding ?

The manufacturer say loose to allow for expansion, but even when nailed loose, I wonder how the vinyl can expand and contract given the orientation of the nail slots. In other words, the side fins have vertical slots, supposedly to allow vertical expansion of the window, however, the top and bottom fins have horizontal slots which would seem to interfere with the vertical movement of the window.
The same could be said about the horizontal movement of the window. (Top/bottom slots inhibit vertical movement; side slots inhibit horizontal movement)

What say ye to this ?


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  1. GBA Editor
    Martin Holladay | | #1

    You've come across some of the "installation contractions" that I wrote about in my JLC article, "Working With Vinyl Windows." Check it out.

  2. Jim Wright | | #2

    Thank you Martin, but that article still doesn't address the question of caulking the fins.
    It also doesn't completely address the nailing slots.
    Why have slots on two edges going one way and the slots on the other two edges going the other way ?
    Seems that for the best relief of expansion, you would want all the slots parallel to the longest dimension. At least then, the window would be free to expand in the dimension that has the greatest expansion.

  3. GBA Editor
    Martin Holladay | | #3

    Here's my opinion:
    1. Install caulk under the side flanges and top flange, but never under the bottom flange.

    2. Follow the manufacturer's recommendation on nailing, even if it seems illogical.

    Trust me -- many window installation instructions are illogical. You need to apply common sense, but don't get obsessive. Windows installed with tight nail or loose nails both seem to work.

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