San Gabriel has a wide range of housing ages in a small area, from properties around the Mission that are genuinely old to post-war tracts and newer infill.
The older buildings bring original materials and original plumbing. Anything on a raised foundation adds a crawl area, which is both where leaks hide and where they do the most structural harm.
What goes wrong in San Gabriel homes
Under-floor leaks are the ones that cost the most, because they run unseen. Joists, subfloor and insulation all take the water before anybody upstairs notices anything.
Newer construction here fails differently: supply connections at appliances, and second-floor bathrooms over living space.
How would I know if there is a leak under the house?
A musty smell that is strongest near the floor, cool or damp flooring in one area, or a water bill that moved. If the crawl area is accessible, a look with a flashlight settles most of it.
Does insulation under the floor need replacing if it got wet?
Usually yes. It holds water against the framing and it does not recover its performance once saturated, so leaving it in place keeps the structure wet.