dpb wrote:

Pete C. wrote:
Doug Miller wrote:
...
Both you and the OP have got the idea so firmly fixed in your heads that a
heat source inside the wall is the only possible cause of this problem, that
neither one of you is the least bit willing to entertain any alternative
explanation.

No, we have objectively analyzed the available information and concluded
that an internal heat source is the most likely cause. ...

I still think the _most_ likely is an external heat source...

Why OP hasn't opened the wall to confirm/deny the indication of an
internal heat source is, I think, owing to being uncertain enough of the
repair process that he thinks cutting into the sheathing is a much
bigger deal than it really is.

Quite possibly.


Where, in fact, the bigger deal is the possibility that Pete is right --
I really don't think that will turn out to be the case as I think the
amount of heat required to produce this external damage if it was
arcing-generated would have shown up w/ some electrical anomalies
although that certainly isn't absolutely required.

I don't think the hear was generated from arcing, I think that there is
a very intermittent arc, perhaps only occurring once that started a fire
in the wall cavity and the fire is what produced the heat before it self
extinguished, probably due to good sealing of the wall cavity preventing
it from getting enough air to really get established.

Also, having some familiarity with PVC I'm pretty confident that the
siding would be dripping down the wall well before it could transfer
enough heat to affect the Tyvek behind it.



The solvent problem I think can be discounted as being too far removed
in time and frankly the damage pattern just doesn't have the shape for
that to have been the cause unless it were a misdirected spray gun blast
and the reported application was rubbing w/ a rag instead...

Either way it's both unlikely that a quick spray of a solvent or a wipe
with solvent on a rag to remove overspray would cause that kind of
damage, much less have it appear suddenly many months later. PVC pipe
and conduit is largely the same thing and it's primed and glued with
solvents stronger than any you'd use to remove some stain overspray and
it doesn't suddenly deform either.


Only when and if OP actually finishes an investigation and reports back
will anything else possibly be learned...

Quite correct. Let's hope we hear back soon.

Pete C.