NE Oregon 20 x 30+ 1.5 story

Started by CabinNick, June 01, 2015, 11:16:39 PM

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I need some advice on how to proceed.....

Last fall we finished the exterior of the cabin but ran out of funds and time to finish the inside.  My plan for this summer is to do the plumbing, electric, insulation, wood stove, etc. and then do all the finish work the following year.  I plan on having a contractor do the insulation and was going to have them put down a vapor barrier at the same time they do the underfloor insulation.  Our foundation is a stem wall/crawl space with 6 air vents.

The snow has mostly melted and I am finally able to get into the property again.  I went into the crawl space today for the first time since last fall to start planning the plumbing.  I pulled up the crawl space access and YIKES!  The bottom of the door was all covered in mold.  I went down in the crawlspace and the floor is covered in places with a thin layer of white mold and there is mold growing on the floor joists.  There is no water in the crawlspace, no sign of water pooling or coming in, and soil is "dry".  I suspect this is just water vapor coming up from the ground and since the vents were blocked with snow up until a week ago the mold just grew over the winter/early spring from humid, stagnant air.

Any advice on how I should proceed?  I will get the crawlspace all dried out, but do I need to treat the mold before insulating?  Do you think this is just due to vapor coming up from the ground?  By code we have to instal a radon vent that is a 4" pipe from below the vapor barrier straight up through the roof like a sewer vent; hopefully that will help with some airflow in the winter.  We are in a very dry climate and the soil that our cabin is built on is well drained but we do have a hill that slopes down to the cabin.  We also receive an insane amount of snow that piles up over the winter as the roof sheds snow.   

Below is a picture of the underside of our crawl space access door (mold was the worst here) and a pictures of one of the I-joists with mold growing on it.   


A 10% Clorox wipedown wouldn't be a bad thing, wear a respirator and glasses/goggles. There has to be a vapor barrier on the ground, tape the seams and mastic it to the walls. I've gotten to where I really prefer to pour a thin "rat slab" whenever I can talk the client into it, it solves lots of problems down the road. The plastic whenever I go back into one is almost always compromised from traffic. If that doesn't get it under control I seal it up and stick a dehumidifier under there with a drain outside.

The worst one I've run into was by a river and creek inlet so humid. The floor was insulated with batts that came down about 2/3 of the joist depth, trashed plastic poorly installed on the poorly graded soil, pools of water on the plastic, AC in the house. I could pinch through the rotten joists below the insulation, the center girder row was rotten. When I lifted the insulation the joists were as new. The exposed wood was hitting dew point often and got into the rot zone. That was basically a rebuild from underneath, regrade, exterior drainage, new plastic and a DH. Don't ignore it.


You need more vents under the building.  My 20 x 30 started to mold before I cut in vents, then it dried out.


In some localities, vents aren't code in a crawl space.  Needs to become an insulated, conditioned space.   I've been in some gawd awful vented crawl spaces where insulation was literally dripping from the floor joists.


Thanks for all the advice on my mold situation.  I think it was caused by a combination of me waiting over the winter before putting down the vapor barrier, waiting over the winter until finishing the final grading away from the cabin, and a problem I think we have with snow deflecting rain run off towards the cabin in the spring.  We get an ton of snow that all slides off the roof and piles up. The overhang and tall roof throw the snow out far.  Then in the spring when it starts to rain, that pile of snow that remains sends all the spring run off directly toward the cabin. 

I spoke to many folks about the mold issue, including a mold remediation contractor.  One extreme of advice was don't worry about it, just spray it with bleach.  The other extreme was pretty much what I ended up doing.  I used all the PPE - respirator with correct filter, googles, suit and gloves.  I waited until the crawl space had fully dried out, then I scraped all of the wood surfaces (yes, every inch of 27 I-joists and underside of subfloor) with a stiff bristle and wire brush to break up the mold accumulations and drop the spores down into the dirt.  I then put down the vapor barrier over the dirt floor and ran it along the walls using butyl tape to secure the vapor barrier to the walls about 6" under the sill plate.  I also taped all seams with a crawl space seam tape.  This weekend I am renting a fogger and will fog the entire space with Concrobium which supposedly should kill the spores and prevent future mold growth.  Scraping that crawl space was absolutely miserable in all that gear, but I wanted to do it right so I didn't always worry about it after I insulate.  Quote from a mold expert to do the work was over $3k.  After purchasing all the gear, equipment rental, chemical and vapor barrier materials I think I have about $500 into the project.  Later this summer (it won't rain here for at least two months now) I am going to install a french drain along the sides of the cabin and finish the final grading.  Next time.....I will do all of this just after I finish the build!

Here is a picture of me in all the gear.  I have been joking that I look like I am going to Walmart in the middle of a COVID-19 pandemic. 


That was the hard route but probably the best.

Just because something has been done and has not failed, doesn't mean it is good design.