Rain leaking in window

A friend of mine has a house stuck on the side of a mountain. Most of the windows face down the hill and are subject to rain and wind often. He's been chasing leaks in the windows for years in the down stairs suite. Now with new tenents he was complaining because he could here the hood fan running all the time, but the windows stopped leaking. Perhaps you get more condensation when the rain is cooling the window.

We had to remove the old heating unit--so it was a good time to inspect the wood underneath. As you can see from the photo no noticeable wood rot. However the sheetrock is a bit more crumbly on the right where you can see the outline of the old heater, so before we insulate and close it up we'd like to remove a little more sheetrock just to check. The right side is where the moisture was more apparent. Of course the old insulation was fiberglass with paper backing, quite deteriorated. So certainly alot of cold air could have gotten in through this combo AC/heating unit over the years. And if when they last painted they didn't remove all the old water soluble wallpaper glue, then that could wick humidity in from the condensation from any cold that blew in. Add that to the stove humidity that could be an issue.

One thing I'll have them look at: on the second photo with the arrows, the green arrow shows where the under-window flashing overlapped nicely, then towards the right it sort of disappears--maybe not put on evenly, so perhaps if it wasn't completely wrapped underneath the window, that could allow moisture entry.

I intend to insulate with either roxul or fiberglass. To make cutting easy I will buy unfaced insulation; given the rest of the house likely has 56 year old paper-faced deteriorated insulation, do I really need to worry about a vapor barrier? I don't like to put plastic over the unfaced sheetrock on the interior given NY's mixed climate. Exterior has 3/4 plywood sheathing, felt paper, 1/4" amoco amocor rigid insulation from the 80s, then shingles.

PS Yes I do intend to caulk any gaps in the sheathing.....

Now would be a good time to hit the outside with water and see if you can find bigger problems. The vapour barrier should be on the inside to protect the wall from interior moist air and gaps in the rough sheeting on the outside allows a route for moisture to get out of the wall but if the foam on the outside is tightly sealed it is also a vapour barrier and now that is a different discussion. If the window does leak, where is the water to go. It can't get outside and you don't want it staying in the wall or getting to the drywall.

Thanks Neal. Will have to wait until shingles are installed to use the hose again. Last week we hosed for twenty minutes and no leakage. now we have a bird's eye view so it will be a better test. I'm leaning towards the other explanations: condensation, cold air infiltration, cooking moisture and old wallpaper glue but we'll see.

I wouldn,t count cold air infiltration for much. Unless there was an open hole to the inside there would be very little air movement. Air looses moisture as it cools so cold air wouldn,t likely deposit any water as it warm up.

If you remove the trim around that window, most often you will find there's no insulation behind it, often you can see cracks all the way around the outside trim where lights coming in.

Cleaning or repairing your window is, of course, a great idea and that you could probably make it work, too. However, considering the age of your window, it may be wise to look into window replacement. You might save money now but eventually, you will have to have it replaced. Windows, just like everything else, has an "expiration". But if you are going to have it reinstalled, it might be a good idea to have a specialist take a look at it first so you do not waste money on something you shouldn't be spending on.

Just to resolve this thread, I thank all for the great advice which will serve me and others faced with troubleshooting window problems. We extensively hosed the window on the outside with no problems. Checked the attic found no water leakage. Peeling paint turned out to be a bad paint job five years ago where the painter didn't remove all the wallpaper glue. In setting up a protocol to troubleshoot these things, I have learned how important it is to listen carefully to the original complaint. Someone might say, 'there's water getting in the window.' They didn't see water, they felt some dampness of plaster and assumed outside rainwater was entering. plaster with peeling paint near a window can allow humidity to enter during storms and feel a little wet but not be harboring actual water. Especially if a through the wall AC/heating unit is not air sealed and lets in cold air and allows some condensation. We've now had the walls scraped, oil-primed and painted with no sign of moisture. The forty year old AC/Heat unit has been removed, wall sealed and radiator soon to be installed. Thanks all.

Most times we do find bigger problems and to often someone just fixes the surface and leaves the bigger problems. It;s to bad you went to all that work, but on the upside there is no doubt about the fix.