It's safe to say that I don't have a lot of experience in home improvement.
I need help!
My dad owns a flowers shop where he has a cooler for the flowers. The cooler has a display window and water is forming and rotting a horizontal support beam directly under the glass window. You can't see the rotted wood from the photos because the beam is in the wall, directly under the glass. I think it's supporting the glass. The white beam you see in the photo is fine and not rotted.
Below the window, a lot of the wall was rotted out, so my dad ripped the wood out and replaced a couple of vertical 2by4s. It doesn't look very good, but he said that the wet wood needed to breathe, so he left a gap right below the window so air could circulate. He just used some thin sheet wood to cover it up.
My plan was to take that all out and replace the vertical 2by4s. I wanted to throw away all of the fluffy insulation and replace it with thick foam insulation board that is moisture proof. Then, I would cover it in plastic. Next, I would cut a piece of wood to fit the open space, seal it off and paint it. This was the plan before I knew about the rotting horizontal beam. Should I replace it? If I seal it off will it just keep rotting? Is there water proof wood? If it does need to breathe should I install some kind of metal vent? I was thinking about installing a metal grill of some kind into the wall so that the air could circulate.
The source of the water is the cooler. You can touch the glass and tell that it's wet and condensation. It's always wet. My guess is that the water is dripping down and collecting on that horizontal beam that is below the glass.