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Window - Frame Gap Issue


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I inspected a 2-year old home built by quote "one of the areas top builders" yesterday. There was a 5x7' fixed window (vinyl framed/insulated glass) in the family room. The window frame (the vertical 7' side) was bowed out in the center approximately 5/16" on both sides. The current owner was told by the builder that this gap was necessary in order to allow the window to flex against the wind.

Opinions on this?

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That's bullshift, to use WJ's term.

Vinyl windows expand at twice the rate of aluminum, wood or fiberglass windows and their rough openings need to be slightly larger to accommodate that additional expansion. Otherwise, the outside perimeter of the window gets constrained and when it expands it has nowhere to go but outward. Ergo, the gaps.

That builder has his head tucked up his assets.



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Thanks Mike.

Your opinion and the reasoning behind it reinforces what I understood about it. The collective opinions of the experienced individuals on this site helps us all report with confidence.

Another window question - more photos attached -Wouldn't best practice be that all exterior window to trim seams be caulked against driving rain?

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That's a seriously cheap-quality vinyl window! I wouldn't expect that to stay leak-free for very long, no matter how well they detail it.

To answer your question, caulk should not be a substitute for good workmanship. If the window has head flashings and you're confident that it's been properly splined (flashed) beneath that trim and siding, it's not absolutely necessary to caulk that joint. If there aren't any head flashings, the caulk is usually used, in addition to whatever has been used behind the trim/siding to flash the window, and essentially represents a figurative pair of crossed fingers while hoping they got the bitumen detailed correctly.

With the vinyl window, the caulk is liable to fail anyway, unless it can move with the expansion/contraction of the window without failing. There is one caulk that might work with that - Big Stretch by Sashco - it's a butyl formulation that doesn't harden and has some amazing elastic qualities. If it's compatible with vinyl and will bond to vinyl and cure properly, it might be worth caulking those joints just to give it a more finished look, but I'd probably leave the bottom un-caulked, just so's there's another path for water to get out from behind the frame and siding should infiltration occur.

I should probably add that you'd normally want to use backer rod in anything wider than about 3/16 inch, but with a vinyl window that's not a great idea, because you'll constrain it. That vinyl will want to expand in summer and that gap is liable to close. Pack it with a bunch of backer rod and you probably won't be able to get them open come summer.

OT - OF!!!


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Since I rarely see them done well, I though I'd post a picture of a nicely flashed window.

Very best practice would be to turn up the ends to form dams instead of turning them down. I think that's what the contractor's done with the lower piece - the ends are turned up and filled with caulk to form dams. At the upper piece, the ends are turned down.

- Jim Katen, Oregon

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On a typical slider window, does anyone have a spec for the amount of allowable gap between the movable sash and the frame?

In other words, when the window is almost closed, one can sight a gap of 0" at the bottom but 1/2" or so at the top.

I recall reading Milgard's specs (don't have them in front of me) and probably remember something about everything must be "plumb and square".

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