Mold around some windows–is there a bigger problem?
I own a house in Portland OR (Marine 4) that is having some mold problems. The mold is in a few diuscrete locations. Primarily, around some window frames (vinyl). The tenant has curtains tacked against the wall to blackout the windows in several of these spots. There’s also a couple kitchen windows that have some mold near the frames. There’s also a spot on the wall where the tenant had left a cushion leaning against the wall for a couple months.
So here’s my theory: the house seems to have fairly high humidity–the tenants have a basic consumer hygrometer showing humditiy levels above 50% right now, sometimes spiking higher while cooking. (It’s been a very wet fall and winter, even by Portland standards). Thus, on the bedroom windows and that spot on the wall, there’s condensation occurring against the cold surfaces. The lack of air flow (cushion; closed curtains) makes them cold and keeps from drying and led to mold. In the kitchen, where there’s no mechanical ventilation, it’s simply lots of cooking and poor ventilation leading to the same result.
Now the questions: Do I need to fix something? Does the overall humidity need to come down? My primary concern is the crawlspace. The house is built over a vented crawlspace that has a very poorly installed sheet of poly laid over the soil. The subfloor is made up of boards, so not much of an air and vapor barrier between the crawl and house. But I get only slightly lower humiudity readings at my house (basement with slab) a few blocks away, with no similar issues. Thus, my thinking is that while I’d love to have a better crawlspace for them (sealed and insulated), the humidity readings and isolated mold lead me to believe the problem is attributable to the localized condensation.
Any advice? I’ve read the mold articles on here and as a result I am personally not too worried about a little bit of mold. But I need to respond to the tenants’ concerns. What I’d like to say: I’ll put an exhaust fan in the kitchen and they need to open their curtains when not sleeping. That should take care of it.
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Replies
Curtains and pillows keep the areas of wall they cover slightly colder than uncovered areas. This means those areas will collect condensation a little sooner than the other areas, so they spend more time being wet. Mold likes wet, so the mold grows there first.
Over 50% humidity is CRAZY high! You’ll have all kinds of hidden mold problems INSIDE your walls, and probably in the attic too, at those levels! 40% is about as high as you should ever go, and even that is pushing it in the winter. Higher than 40% shouldn’t ever be necessary for comfort.
I doubt you have anything wrong aside from running the humidifier WAY to much, but I’d check in the attic for signs of damage, along the rim joist if it’s accessible, and try to pop a few electrical box covers off on the inside of the exterior walls and see if you can see any moisture/mold problems around those inside the walls.
Bill
Thanks Zephyr. I'll do some more investigation for other damage. They were using a humidifer in the past, but haven't been for several weeks. That 50% reading is current.
I just checked my house. 98% RH outside at 50F; 50%RH inside at 70F. A quick calculation shows those two as nearly identical in absolute humidity. So 50% seems reasonable. It may be high, but such is life here in the cold, damp, PNW: dropping it would require a dehumidifier.
Bill,
Here in the PNW you will have a hard time getting down anywhere near 40% indoor humidity all through the year. I use my wife's she-shed as a proxy for a building that is heated but not occupied, and it stays within 3% of the humidity in our house, which right now is 48%.
Thanks for confirming my expectations, Malcom.
So considering all these PNW houses without a means of dehumidifying aren't all moldy, is it safe to say then that if I fix the localized condensation this problem should resolve? I.e., I think I can rule out the crawlspace as creating the problem.
Based on what Malcolm said about “regular” humidity levels in the PNW, your tenant should absolutely NOT be running a humidifier. My guess is that humidifier is the source of most, if not all, of your mold problems.
Bill
Gary,
The moisture problems in the building assemblies of houses here are almost entirely due to exterior bulk water infiltration - and that the exterior air used as ventilation for roofs doesn't help dry much.
The high interior RH doesn't generally cause problems on it's own, although it doesn't take a lot to get mold started if there are additional sources of moisture or cold surfaces, so localized spots can appear in bathrooms and window frames. Closed off rooms with lower heat, or night-time setbacks of the thermostat can also contribute. Any humidification is nuts.