Window Glass Anomaly

I need some help identifying this anomaly.

Newer (within 5yrs) insulated windows have staining or what appears to be a mold like substance. This was found in one upstairs window, and two 1st floor windows. The stain was on the inside of the exterior glass.
There was no stain behind the muntins, viewed from the inside. No condensation noted. Outside temp = 35F / inside temp = 62F. Water boiler heat.


It sounds like it is between the panes of glass which would indicate leaking insulated glass at the window. Report what you see.

mfr defect
LowE coating failure

also verify Low-E coating surface for your climate with the mfr at all locations

Low E - How does it work?
Low E glass coatings work by reflecting or absorbing IR light (heat energy). The thickness of the Low E coating and the position in the window (#2 or #3 surface) dictate how the window will perform.
Northern-When installed on the #3 surface of an insulated glass unit (IG), the Low E coating will reflect IR heat from inside the room to help reduce the energy loss during the cold months, thereby reducing heating costs. View flash demo
Texas/Southern- When installed on the #2 surface of an IG unit, the Low E coating will reflect or absorb IR heat from the outside, thereby reducing solar gain and cooling costs during the warm months. View flash demo

Could it not just be a fogged window? I really like the education Barry but if it was 35F outside the moisture inside the window would have frozen and left marks like you see in the pictures. A fogged window would also need to be repaired/replaced.

Thanks Barry, good information. I had wondered about the low e coating being in the wrong place, but never dawned on me that the actual coating may be defective.

Would a *(local)*glass company be able to confirm this theory?

Hi Greg, how are you? I’m not Barry, but most times the glass I’ve seen, has a definite fog like appearance when the seal is broken, but this one is a real tester.


Low-E diagram.jpg

i’ll stick with my orig id until proven wrong ;~))

No Problem Jim. Just trying to wrap my head around it is all.
This is a window from Friday. No mutton bars but the same kind of issue that you are seeing. I wrote it up as a thermal seal failure. It would be interesting to see what Barry has to say about it. If I was wrong in my analisis I need to know so I can call it out properly in the future. This was the only West facing window.

Did not take a great picture of it from the inside as the buyer had already written in to their contract to have it replaced.

To me…that looks like a broken seal.

seal failures that exhibit an efflorescence like coating on the panes are 1 thing
my exp: Low-E failure on newer units appears as golden-grayish streaks or spatter markings

when unsure play it safe & just report “obscured glass anomaly observed” & let the glass expert tell them the cause & $s to replace

Good info as always Barry. Thank you

Ditto on the Thank You…

ready to close brand new 2013 shaq
what’s the issue w/windows?


IR_0343 (Small).jpg

Barry is correct. In almost 99% of this type of failure it is the low e film that has failed in the contact with the glass. In the other 1% it can be a failure of the suspended film in between the panes of glass. These films are used in place of a 3rd pane in super insulated windows.

It is a manufacturer’s defect BUT most manufacturers have changed their warranties to only cover the original owner of the window. It is important that you tell your client to have the seller put in a claim under any existing warranty before close of escrow. The sellers may be covered, chances are your client would not be covered.

#1) broken seal
#2) seal between the glass blocks is failing