What to do if you suspect mold in your home
Is the cabin conditioned year round or at all?
Are there any grading or moisture issues that are allowing bulk moisture into the crawl?
Conditioning the crawl is usually the best answer but if it is sporadic use and/or makes better sense to leave as a vented space, you need to do the following for optimum performance:
- Install a vapor barrier across the floor. Seal all piers and penetrations as well as seal to the stem wall.
- Insulate the underside of the floor and ideally thermally break the floor joists from the earth.
- This is best accomplished by covering the floor joist with a rigid foam and sealing all the seams.
When you say vented to the roof, do you mean into the attic UNDER the roof, or through the roof with a duct up through a roof jack into a roof hood ? Hopefully the latter, otherwise you have the likely source of the problem.
You are clearly getting moisture in this area still, so more insulation will not help and may hurt - insulation does not stop moisture but does trap it, particularly if you add enough tht the freezing front moves well down into the insulation, so vapor coming up from the house freezes in the insulation (making it wet when it thaws) rather than venting into the attic and evaporating from there.
You need an expert check on the bathroom area - that the fan unit and any light fixtures are tighly sealed to the vapor barrier. Usually they are installed with about a 1/4-1/2 inch void all around for ease of installation, and not sealed at all, so moist bathroom air vents around themm into the attic.
Then the fan unit needs checking for openings - many have openings in the plastic or metal case from manufacturing that are not sealed but should be. Do NOT use any type of unit that, because of big lights or heat lamp, says it has to be vented and cannot be sealed in, because moist air goes right up through it.
Then the duct from the fan up through the roof needs checking for leaks (and should be insulated, at least if your attic goes below freezing ever), and should have a roof jack where it penetrates the attic - a rubber seal in a metal plate that fits tightly around the duct, so the air blown into the vent hood on the roof cannot circulate back down into the attic. Most installers just cut about a 1 foot opening in the roof (especially if they can install the duct that way without having to crawl around in itchy attic insulation), run the duct up through it into the roof hood, and walk away. That leaves that big opening in the roof sheathing for the wet air and condensation in the hood to corculate right back down into the attic. Some installers (like my house whenn I first bought it) really take the easy route and don't even connect the duct to the hood - they just terminate it a foot or so below the sheathing so ALL the moist air goes into the attic.
I would also check the kitchen and any other bathroom fans for the same leak sources or improper installation, and make sure all vent pipes are intact to above the roof, and that there are no furnace or HVAC ducts disconnected or damaged that could be adding moisture.
Also look around all roof penetrations for ducts and pipes for staining on the underside of the sheathing, which would be indicative of roof hood or jack leaks that should be repaired. (Hopefully, with a new roof you would not have any).
The area most affected should have the insulation moved away and checked to see if the vapor barrier has holes or tears, openings around pipes, ducts, light boxes or wiring, or was maybe totally torn out by some prior workman. If your vapor barrier is not effective, moist household air will move into the attic almost year around, but especially in cold weather, carrying moisture into the attic, where it will condense and cause mold.
Also - if you have a fireplace chase (wood boxout around metal chimney) in that area, it may connect to the house in the firebox area and be open to the attic (which is a real fire spread hazard but for some reason is not contrary to code), letting household air flow by that route.
The mold should be brushed and vacuumed away, then treated - there are commercial sprays that are fungicides that commercial mold and mildew removal contractors have, a sprayed chlorine bleach and borax solution has also been shown to work but you would have to have an air supplied respirator and chemical suit to work with that, which only professional remediation contractors have. Do NOT paint the area - especially the underside of the roof sheathing and trusses. They needs to be able to breathe, not have any moisture from above locked in.
Stains in the attic (assuming this is an unoccupied area) can be bleached, and then if you want the evidence to go away and make it easier to tell if there is new staining or mold, sanded to remove the worst of them.
Stains on areas visible from the outside like walls and rafters can be treated with Chlorine bleach (beware of dripping on good finishes below), painted with Kilz or similar anti-fungal primer, then painted. Stains on the underside of the sheathing visible in the soffit area can be bleached and then when dry, sanded away.
Ventilation is essential, but without removing the source of most the moisture you will not win this war no matter how many times you battle it.
While I would guess the fans and vents are the problem, is there anything different about the attic ventilation to this area versus the other parts of the roof - soffit covers, blocked eave openings, insulation-clogged bug screening or soffit cover openings, lack of air chutes or eave baffles, insulation pushed up against eave opening or up against roof, horizontal blocking that prevents or obstructs airflow, no ridge vent above it, etc ?
If you are not able to find an obvious source of the moisture, I woud consider getting a thermal IR scan of the attic. For typically about $200-300 an energy conservation expert with thermal scanner can scan the attic (might have to be done at night or VERY early morning if done in summertime, to accentuate the temp difference between house air and attic air, unless you have AC in which case turning the AC down low and blower on full can work by pushing cold air rather than hot up through any gaps or voids. If you have that done, check on price to add in the rest of the house too - probably not more than about $100 more, and can show you where your air leaks and poor insulation air. You should try to get one who can provide the entire scan to you on CD or DVD, so you can review it in the future. Here is a link to some images so you know what I am talking about -