Mold Under Vinyl Siding and House Wrap
Vinyl siding is not airtight, and it is not designed to be the primary water barrier; that job belongs to the house wrap or building paper installed underneath it. When that layer is missing, torn, or installed with the laps running the wrong direction, water that gets behind the siding, which happens routinely, reaches the wood sheathing directly and has nowhere to drain back out.
This is a slower-developing problem than a roof or plumbing leak, often taking years to become visible from the inside, which is part of what makes it easy to miss until sheathing damage is already significant. Homes that have had siding replaced or added onto without re-wrapping the wall underneath are the most common cases we see.
Because the damage is structural (rotted sheathing, not just surface growth) once it is found, this is one of the cases where remediation and repair are the same project, not two separate steps, and it is worth having someone who does both look at it together.
Common questions
How would a homeowner even know this is happening?
It usually shows up as a soft or discolored spot on interior drywall near an exterior wall, or as visibly rotted sheathing if a section of siding is ever removed for another reason, like adding an outlet or fixture.
Does this mean the siding itself needs to come off to check?
Not necessarily everywhere, but if there is a known problem area, that section is the reasonable place to open up and inspect, rather than assuming the whole house wrap has failed based on one spot.
Not sure what you are looking at?
Send a photo and rough measurements, or call and describe it. We will tell you whether it needs a professional.
Request a Free Inspection Call (717) 420-1964