How do I best inspect for moisture impact in the exterior wall?

[Radhusfarsan]

Hello,
New owner of a two-story terraced house from the late seventies here. We have an unusual smell in a room on the upper floor that I can best describe as musty. It is only present in that room. I suspect it is due to moisture effects from the exterior wall, where the wood paneling generally seems okay but where it previously (an unspecified number of years ago) leaked into the storage room on the ground floor, whose roof is joined to the relevant exterior wall. When I remove the baseboard, it also seems to feel the best against the exterior wall, especially in the section above the storage room.

Now to my question:
Is it feasible for me as an inexperienced amateur to open up the drywall in the interior wall to try to inspect it more closely? I am mainly interested in the studs. I suspect I may encounter a vapor barrier beforehand, and once I make a hole there, it could be tricky to repair (how?) through my inspection hole. And how much will I even see through my hole of, say, 20 cm? I will try to go in the middle of the stud in the risk area but would like to get an overview so I can draw conclusions.
Other better suggestions? Anticimex and Ocab apparently don't do anything that invasive themselves based on the information I got when I called. It was even the guy at Ocab who suggested that I could open the drywall myself as I had already done the work they usually do.

I understand if these are difficult questions to answer, but any help would be valuable before I cause trouble for myself and my family.

 

[Håbbe01]

Common areas in older houses from the 70s often have the sill made of pressure-treated wood and lack a moisture barrier against the foundation, which creates a musty smell. The smell can certainly creep up higher in the exterior wall. But opening up and checking is not a big job.

 

[SågspånPappspikEternit]

Can't you start by inspecting from the outside, i.e., remove a few panel boards in the suspected area? You can just nail them back afterward. If the moisture is coming from the outside, isn't it better to address the source directly, instead of starting to tamper with interior walls and vapor barriers?

 

[Radhusfarsan]

The common issue with older houses from the 70s is usually that the sill is made of pressure-treated wood and lacks a moisture barrier against the ground, which creates a musty smell. It can certainly creep up into the outer wall. But opening it up and checking is not a big job.

Wouldn't you notice it in the crawl space? Sniffing along the baseboards in other rooms, you don't notice anything.

My new hypothesis is that it's old damp fiberboard I'm sensing. I found a gap by the storage roof where it opened directly onto the fiberboard, which after heavy rain had become noticeably damp. Very poorly done by whoever built there. It likely happens during most rainstorms. I have temporarily fixed this, but it needs to be done better. And the question is whether it is possible to get rid of the smell without removing the fiberboard—or if the moisture might have caused worse effects in there.

 

[Håbbe01]

Wouldn't you usually notice it in the crawl space? Sniffing along the baseboards in other rooms reveals nothing.

My new hypothesis is that it's the old damp asfaboard I'm noticing. I found a gap at the storage ceiling where it was wide open to asfaboard that became noticeably damp after heavy rain. Very poorly done by whoever carpentered there.
It probably happens after most rain. I've temporarily fixed this, but it needs a better solution. And the question is whether it's possible to get rid of the smell without removing the asfaboard - or if the moisture may have caused worse effects inside there. T

I think the smell should be aired out if there's a gap, one might think. Have you checked in the crawl space to see if it is intact?

 

[Radhusfarsan]

Can't you start by inspecting from the outside, i.e., remove some panel boards in the suspected area? You can just nail them back afterward. If the moisture comes from outside, it’s better to address the source directly, instead of starting to cause damage to interior walls and vapor barriers.

That doesn't sound like a bad idea, especially since I think I’ve been able to trace the original problem to a defect in the facade and a faulty silicone seal on the shed roof, both of which probably have contributed to moisture being absorbed into the asfaboard inside the wall.

The problem with the approach from the outside is that I can’t see behind the asfaboard, but I guess I’ll have to remove a piece of it then, and close it up as best as I can.

 

[Radhusfarsan]

I think the smell should ventilate out along the way if there's a gap anyway, one might think. Have you checked in the crawl space that it is intact

I have explored the crawl space and there is no strange smell at all. That makes smell from tryckt syll unlikely, right?

 

[Radhusfarsan]

I think the smell should then air out along the way if there's a gap. Have you checked in the crawl space to see if it's intact?

Clarification, the exposed asfaboard is located approximately at floor level on the exterior wall where I smell it in the room.