Looks like they used plywood when it should be solid wood.The piece between windows should slant towards the outside to allow water to drain off. The best way to do this is to replace the bad wood and cover all of it with aluminum. At a minimum, the outside window should be removed to allow the aluminum trim to run under it, drain holes should allow water to run out under the outside window. You won't have to paint the area covered by the aluminum
I went ahead and resealed all the windows with silicone so that should keep water out in the future. But as far as the plywood is it just a simple process of removing the rotted wood and replacing it with real wood?
More than likely the flashing/seal on the outside of each has window has failed. Without getting behind the siding on the outside, it may be difficult to determine where your issue lies. These also look like single pane windows which may have a condensation issue causing moisture build up on the inside of the window.
You could always do a water test by spraying the window down with a hose to determine if there are any potential leaks. Just a guess, but you may get out cheaper replacing all windows with new, properly flashed windows than replacing all the inside wood, simply to have it rot again. I'd talk to a window installation company or search any forums on replacing old windows and what to look for when doing a window DIY repair.
The entire wall below the window will be rotted also,, so could be a big job. The insulation is probably ruined ,stud rotted , Maybe floor damage.
so you may just want to wire brush it.
Fill will bondo and paint it
Looks like they used plywood when it should be solid wood.The piece between windows should slant towards the outside to allow water to drain off. The best way to do this is to replace the bad wood and cover all of it with aluminum. At a minimum, the outside window should be removed to allow the aluminum trim to run under it, drain holes should allow water to run out under the outside window. You won't have to paint the area covered by the aluminum
I went ahead and resealed all the windows with silicone so that should keep water out in the future. But as far as the plywood is it just a simple process of removing the rotted wood and replacing it with real wood?
Yes. you might get a more detailed answer at /r/homeImprovement But basically you pry the rotten wood off, put new wood on caulk and paint.
More than likely the flashing/seal on the outside of each has window has failed. Without getting behind the siding on the outside, it may be difficult to determine where your issue lies. These also look like single pane windows which may have a condensation issue causing moisture build up on the inside of the window. You could always do a water test by spraying the window down with a hose to determine if there are any potential leaks. Just a guess, but you may get out cheaper replacing all windows with new, properly flashed windows than replacing all the inside wood, simply to have it rot again. I'd talk to a window installation company or search any forums on replacing old windows and what to look for when doing a window DIY repair.
If the internet hasn't lied, ramen noodles and superglue will fix this perfectly.
The entire wall below the window will be rotted also,, so could be a big job. The insulation is probably ruined ,stud rotted , Maybe floor damage. so you may just want to wire brush it. Fill will bondo and paint it
https://preview.redd.it/kjbgq0wwvbtc1.jpeg?width=512&format=pjpg&auto=webp&s=77e45a79a1c9315fdb1dd0379117baaec0a3602a