Green water mark under the window

Hello, All

I already saw two of this kind of condition under the window. I know it is water or wet condition to make this green mark. But I really want to know why and I want to explain to my client how to fix and where need to pay attention in the future.


And what happens if you are wrong? :flushed:

Well, the you get to pay for it and then some if they get you into court. :heavy_dollar_sign:

One would do better describing what one sees and then referring it out to a qualified professional, IMHO.


nice point, learn it. Thanks

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Just throwing this out there as one possibility, Window rough openings are designed to be 1/2’’ wider and 1/2’’ taller than the window, which allows for a 1/4’’ gap on all four sides of the window, allowing for insulation on all four sides, most builders set the window directly on the rough framing leaving no room for insulation at the bottom of the window creating condensation, The window should set on 1/4 shims allowing for insulation at the bottom. Not saying this is what is happening in the OPs pic.
images (2)


Thanks a lot for explain. Yes, it is normally happen in the construction site.

Photo 2 is different than photo 1 in some ways. Both windows on the same house?

Hi, Brian

They are different houses.
Each house only have one window like this, all other windows are normal condition.


Here is my take.

Window 1 - dirt, grime or soot which collects on the window ledge, window weeps etc. washes down during rains and is collected in the rough surface of the stucco. Dirt/grime and damp conditions may promote mildew/fungal growth which can be exacerbated depending on which side the home is facing (North).

Window 2 - Similar as above but that stain appears to be concentrated. Home owner may leave damp towels, AC units, hanging plant etc. Gutter may overflow/leak here.

A giant umbrella or huge circus tent…

Likely won’t grow algae if it isn’t damp or wet.

Maybe a drip cap above and a drip edge below might be a touch easier to install.

Of course, but it won’t stop the wall from getting wet everywhere else, and stucco holds moisture like crazy with all the “nooks & crannies”. Rain goes just about everywhere on these open walls.

“Evidence of rain water being improperly reserved and draining out of the windows. There is a possibility of damage and rot to the framing in the area. Evaluation and correction is recommended by contractor familiar with exterior systems.”

In general, never tell a client how to fix anything. Even if you tell them exactly the correct way to do it, they will hear what you said and do the work based on their own experiences, knowledge, and abilities which may not be good enough for the job…and blame you for their failure.

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I own two Stucco houses, and there are 10s of thousands of them within a few miles without this issue. Something is clearly different, but all these have sills and such so water doesn’t sheet down the side. Maybe the paint? That said, maybe there is a bulimic living there and frequently boots out the window?

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Perhaps, but I too am in the land of stucco, it’s literally everywhere. I see this condition in a variety of localized spots on tons of stucco homes, typically in the shade or on walls prone to excessive wetting. Poor maintenance doesn’t help either.

its most likely the drain holes in the windows are clogged allowing rain water to slowly trickle out. Recommend cleaning the window weep holes and cleaning the siding with a fungicide.

On this one, I’m thinking they cleaned the walls with some type of solution that washed out all the grime collected at the bottom of the window. You can see a white residue on the screen.

On this one, the whole area looks darker to my eyes and may be saturated with moisture. Possibly from over-eager pressure washing and/or water penetrating at the bottom of the windows.

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Blocked clogged gutters.
WINDOW OPENING Missing drip cap.
Suspect: Microbial growth.
Caulking issues.
Ssuspect: EIFS issue. Look above vertical expansion joint. Color change.

And if that doesn’t work, they’ll be calling you because you said it would work. and, now they want you to pay for any repair needed to make the real correction.

Why not just refer it out and save the headache and :heavy_dollar_sign: ?


Looks like more than a weep hole issue. That green is likely algae, and it takes persistent moisture for algae to grow. I think this will be a costly repair.


True, but why not look on the inside of the window and see.