You may be right there's a leak, but I haven't been able to find it.
I pulled off the trim on the interior wall that's next to the darkened
spots. The floorboards end short of the wall and I can see the
subflooring, which is dry (except for one tiny spot which might be
damp, I can't tell, but can't be the source of all that water).
So that eliminates the water heater vent as a source of the water.
There's a layer between the floorboards and the subflooring, so that
explains why no water is showing up in the subflooring. Water could
travel for a long ways under the floor.
Just to the left of the area in the picture there's a pergo kitchen
floor. Water could be traveling under that floor and I'd never know
it. It would have to be coming down an exterior wall.
That's the *only* path under the floor that water could be traveling,
to reach the darkened places. There's a doorway to the right of the
area in the picture, but the flooring to the right of that area
doesn't have any darkened spots, and it's actually lower than the
rest of the floor, there's a slightly sagging area of floor there.
Otherwise, the wood floor isn't covered and there aren't any other
areas with darkened spots.
I looked at the underside of the subflooring under the kitchen floor,
hoping to see some wetness near the walls, but I didn't.
I went up into the attic and looked at the underside of the roof
over the kitchen and I didn't see any leaking. There might be some,
I have a low-pitched roof and there's stuff like clumped up insulation
and ventilation baffles cluttering things up between a lot of the
rafters near the walls. So far as I could peer with a flashlight,
without doing a lot of work to pull out clumped-up insulation and
tear out ventilation baffles, everything is dry.
There's a rain gutter going down the side of a kitchen wall (not
close to the darkened area). But I checked to see whether that
might be leaking and the wall and everything look dry.
My eaves are about 2' wide and it isn't possible that a significant
amount of rain would be getting into the wall from the side. It
hasn't been windy.
The floor area that's getting darkened is about 15" above ground
level, so I don't see how water could be coming up from the ground.
What I was thinking is that water could have been trapped for months
under the floor, between the flooring and that layer right under
the floorboards - and it's always wicking up, only it's not visible
when the humidity is lower, because it's wicking up slowly and when
it's drier, the water evaporates well enough as it wicks up so that
it can't be seen. The reason that might be right is that the
areas that get dark are pretty much right under where I park my
bicycle. It does look a lot like rain is getting in somehow, though.
One other possibility - there's a sewage vent pipe going up inside an
exterior wall. That's the only roof vent over the kitchen - well,
there's a roof ventilation vent, but that's quite accessible and I
didn't see any sign of leaking around it.
The sewage vent pipe goes up to the roof behind kitchen cabinets so
I can't check around that area. I sealed around this vent really
well with tar ~ a month ago - perhaps I missed something though.
When the roof dries out I can go up there and take pictures and maybe
someone can tell me if it looks like it could be leaking there. Once
you've eliminated all the likely explanations, the one that remains,
however unlikely, must (?) be the truth :)
Water would have to travel 10-15 feet under the pergo floor to get
to the place where the darkened spots are, though. Perpendicular to
the way the floorboards are laid.
I don't know if the floor is sloping, no level and nothing metal
(hydrophilic) to try to fill with water. Only a plastic spare storm
window which is not helpful.
yep, mysterious floor leak!