One, Two, Three, You Can't Hide From Me!
The First Clue
Here the street face of the painted basement concrete wall is blistered.
The other adjacent units are not. They have smooth solid paint surfaces.
Blistering paint is caused by water escaping from underneath.
This means the walls are wet or are getting water from some where.
The most common sources are conditions found higher up the walls or from the roof.
The Second Clue
This is over head on the same front wall. This is the roof soffit.
Now the dirt on the top of the siding is not surprising or rare.
However the streaks are caused by running water (there's no other cause).
The water has to come from higher up. What's higher up? Nothin' up there but the roof and sky. No not the sky, this is under the soffit.
This roof has a curb (parapet wall and party wall curb) on three sides.
When winter conditions have frozen the drain, the next route off this roof is over the front edge, because that becomes the lowest point till the drain unblocks (thaws).
So winter rains an snow melt aren't going down the drain as planned.
Instead the water is finding other ways.
So now we know here the water in the front wall is coming from.
The Third Clue
The first two have already got us to the roof, but this clue means its on going over time.
Why? The metal brick ties have had time to rust out and let go (break).
As this takes a while it means the brick ties keep getting wet.
That means water is getting in this wall on a regular basis.
Parapet Wall Detail: This is the top of that wall with the bowed masonry.
That's an unusual vent fitted into the parapet wall flashing. In the summer it probably works fine airing out the roof framing space.
Winter changes everything.
Add some snow, a layer of ice and a frozen or blocked drain and it wont take long to convert that vent into a drain.
Under those conditions it's just a funnel to put water directly down into that wall.
So what else is there to see on this roof:
Open and Rusted Flashing Membrane Bulge/ Blister Membrane Ridging
This all adds up to a new roofing job being required immediately : Budget to replace roofing immediately. Provide scuppers and standard gooseneck roof vents.
N.B. Look for a following article on why some changes affect other building components and can disrupt their function. It will be titled;"Ch Ch Ch Changes"....Don't Always Improve (Your Roof, Your House) IT.