On first look things may not be what they appear
Age and experience should teach us that what we see may not be in fact what we get. While performing a home inspection an incorrect or hasty conclusion could be cause for more than embarrassment. Fortunately, most often a red faced retraction is the often the worst outcome.
Experience has taught me that one thing usually leads to another, but there could be something else happening not so apparent. That what is being seen at that moment may be nothing more than a symptom of another problem else where in the house. Take for example frost and water on the roof sheathing in the attic. Often the knee jerk reaction is that the attic lacks adequate ventilation.
Attic ventilation seems to be thought of as the ultimate eliminator of two undesirables from the attic, moisture and excessive heat. While it is true ventilation serves this purpose, it also has a limit. Ventilation can not overcome copious amounts of moisture from typical sources like bathroom exhaust fans that have been vented directly into the attic space. While other sources may not be so obvious. To complicate things further other variables may also be at play, creating conflicting information.
Such was the case during the inspection of an attic where excessive moisture presented it self in the form of condensation, staining and fungal growth on the roof sheathing...
On just one side of the roof.
Experience has taught me that one side of the roof sheathing being clean is typically due to the house's orientation to the sun. A warm surface will not condense moisture. It's not that there is less moisture here or that some undetectable moisture barrier is dividing the attic in two. Its that warmer surfaces and warm air are able to hold more moisture. The dampness is still present, just invisible.
So what is causing where is the moisture coming from?
The usual suspects were not in play. Bath vent in attic, nada. Old, minimal insulation and a ceiling plane that looks like a gargantuan piece of Swiss cheese, nope. HVAC system in attic or one with a humidifier, no and no. House has baseboard heat. Good, adequate ventilation present, yep.
The most likely source at this point is the place furthest from the attic, the basement. And here the likely culprit was found to be an unlikely source of moisture, the boiler.
The floor had a large and growing puddle of water around the boiler. The unit's tank was cracked, had been for a considerable time, resulting is a constant source of moisture. And because the domestic hot water was from a tankless coil in the boiler, the unit ran and leaked all year.
So while on first examination, the excessive moisture present in the attic could be thought to be due to a lack of adequate ventilation, in fact it seems to be an entirely different and uncommon cause in the basement. It is often best to keep ones own council until all avenues of information are explored.