Glendale spans a lot of ground and a lot of building types, from mid-rise apartments near Brand to hillside houses up against the Verdugos. The losses differ completely between the two.
In the multi-family stock a single failure travels vertically through several units. On the hillsides it is drainage, and a wet winter is what exposes it.
What goes wrong in Glendale properties
Apartment losses usually start with a supply line, a water heater or an angle stop, and gravity does the rest. By the time the unit below reports a ceiling stain, the assembly between them has been wet for a while.
On the hill slopes the issue is where water goes when it arrives quickly. Runoff finds the low point, and a garage cut into a slope is frequently it. Retaining wall drainage that has clogged is the usual cause.
Water came through my ceiling from the unit above.
Get the source stopped first, which usually means access to that unit. Then document everything before anyone cleans up, because responsibility between units and the association depends on where the failure was.
My hillside garage takes water every big storm.
That is a drainage problem rather than a waterproofing one. Look at where the water is coming from before sealing anything, because sealing the inside of a wall under pressure does not hold.