Pella double hung vinyl windows bowing


Old 09-15-13, 05:49 PM
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Pella double hung vinyl windows bowing

I had Pella double hung therma star vinyl windows installed from Lowes back in October of 2006. They replaced old wood windows with storm windows. Problem is that now on 4 of the windows the bottoms have bowed up towards the center. I am going to post a picture its kinda hard to tell in the picture. I am wondering what could cause this and if anyone has any suggestion's.
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Old 09-15-13, 06:05 PM
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Thumbs down to the installer. Couldn't bend trim coil to look like brick mold and it was too much hassle to bother making a sill plate......I shake my head.....

Your windows are flexing from pressure. Either cranked down too hard during install or too much insulation was stuffed into the wall cavity.

Open the window and look at the track that the window rides in on each side. You should see a plastic insert that will slide up if you apply force to it. Underneath you will find a screw hole. Put a phillips head screw driver into the hole and back off the screw a half turn on each side and see it that reduces the bow.
Old 09-15-13, 08:20 PM
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I will agree it's a crummy example of cladding, especially since the step sill and blind stop was not covered at all after the storm window was removed, leaving bare wood exposed to the elements. But I would also add that not every house has trim in the style of a traditional brickmould. Also, I would suspect that the cladding predated the window installation and that the Lowe's installers were only contracted to install the replacement window, not replace or do any additional cladding. While it is crummy that they didn't do it, that's probably the way it is. Lowes salesman probably asked, "Do you need to have your exterior trim clad in aluminum trim coil?" Most homeowners who don't know what parts will be exposed once the storm is removed would say, "My windows are already wrapped with aluminum trim coil". Therefore that step was not included in the price. You would think that would be included, but I bet it's not, and the installers don't usually do work that they aren't contracted or paid to do. Some would bring it up and inform the homeowner, some won't. Cladding windows usually runs from $40-$70 extra per window opening, depending.

Having installed vinyl windows for about 22 yrs, I would say that there are multiple things going on here.

1). This is a low quality window with a thin sill. Just look at the thickness of the sill where the sill expander starts, (just below the weep hole) and where the bottom of the screen begins. That's maybe 1/2" thick. No wonder it bowed! There's no meat there- no structure to the frame to give it any rigidity. The sill structure is probably shaped like a hollow box with very little or no vertical wall structure in the vinyl extrusion. Low quality windows also have thin vinyl extrusions that are wimpy and flexible, while better windows have thicker, heavier extrusions with multiple right angles and chambers within the extrusion to give the frame strength and rigidity. Simply having the Pella name does not ensure quality.

2). The window does not appear to be sitting solidly on the sill. (not only in front, where the caulk is, but probably not in back either, at the interior side of the sloped sill.) Sills generally have about 10 of slope, and when the window is sitting solidly on the interior (high) side sill, the sill expander will usually need to be roughly 3/4" high on the exterior (low) side of the sill. I would guess that the sill expander in the picture is 1 1/4" wide AND it has a 1/4 - 3/8" gap under it that has been caulked! So that window is definitely sitting up in the air, suspended above the sill. If they didn't put any shims under the window to support it, then it's likely that the window is moving around a little since it isn't solidly sitting on anything substantial.

I'm fairly certain that #1 and #2 put together are the reason these windows are bowing.

3). if the installers crammed too much fiberglass insulation under the window as czizzi mentioned, it could be that the pressure from that tightly packed insulation has finally succeeded in popping the caulking loose, bowing the sill up. Or maybe they blew expanding foam under it and it's been bowed this way for a while and only when the caulking cracked a few years later did the homeowner notice the bow.

I also don't think that any sort of screw adjustment on the sides is going to do anything to fix this problem. The windows probably need to be pulled and reinstalled. They definitely need to be re-clad.

The only possible solution that doesn't involve removing and reinstalling the window would be to remove all the caulking below the sill expander, drill one, two, or three 3/8" holes in the 1st layer of the sill, and install some pan head stainless steel screws through the sill of the window, chasing the threads with sealant as the screws are driven. The 3/8" holes would then need to be filled with a 3/8" white vinyl plug. This is pretty common... I used to do it all the time on window installs where you had a pretty wide double hung that was likely to bow because it was so wide... I did it as a preventative measure to eliminate a call-back for this very reason. I have seen the 3/8" white vinyl plugs sold in the hardware aisle at box stores, in the drawers of miscellaneous screws / other hardware.

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