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need advice on making my nearly finished walls more breathable.
I'm in lake country Minnesota.  I used inch and a half foam board and Roxol mineral wool, a house wrap on the exterior Sheathing and sealed the interior walls with poly tarp.  The siding has not been installed yet the interior walls are wall board and cheap ply wood type board. 

The south facing wall I put on some of this cheap ply board to help remedy a leak through the Sheathing seems that came on heavy driving rains.  Eventually this got mold on it so I cleaned it off with bleach a painted it as well as sealed those seems with calk.  The window trim was done before hand.

I don't have electricity yet and the air quality is getting a little poor in there.  I'll wake up in the morning and it feels cool and a little damp.

The floor is almost fully insulated with spray foam, as well as the ceiling.  I do know that some moisture is coming up from beneath the floor, but this will be remedied soon as Im building a proper block foundation and will be moving the cabin (10x16') into it. 

So Ive been reading up on this site about making breathable walls.  I've heard a lot of different ideas. 

I'm looking for inexpensive siding ideas.  Should I remove the house wrap before I side? 

Should I make some cuts into the interior walls and remove some of the poly tarp?

At first I was going to do cedar shakes for siding.  They are pretty affordable but I got worried about putting too many holes into the Sheathing.  Now im worried of moister collecting in the walls and putting some holes in the walls seem like it could help allow moister to exit. 

Thanks.  Im new to the site.  I hope this is a good page for this topic.

Hi Nick,

Can you include some photos (especially of the leak in the south wall) and maybe describe your wall construction layer by layer from outside to inside?  I'm not sure from your post if your house wrap is against your sheathing or if it's your outermost layer.  What did you use for house wrap?  How far does your roof overhang your exterior walls?

House wrap is supposed to be breathable but impervious to liquid water.  I would suggest tying into your mineral wool layer to let your wall breath.  Mineral wool is a great place to stop water, let it wick away and allow for some airflow.  Without having a complete picture of your wall construction, I'm thinking of some accommodation for venting under your eaves and the capability to weep at the base of your mineral wool layer.

Please keep in mind that the weeps and vents will allow for some natural convection and have a general cooling effect on your building.  You're dealing with the balancing act of having a super tight home for the sake of energy efficiency but not making things so tight that you have poor air quality or worse.

I'd like to have some more information before I weigh in on what's going on in the interior of your home.

If your wall is constructed correctly, your siding layer does not have to be impervious to water.  The only reason I can think of to adjust your house wrap is to prevent water from damming up behind it.  Check out the image I included . . . a picture is worth lots more than my gabbing. 

Here is one possible example of how to incorporate mineral wool into stick framed wall construction.
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Interior pics
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Thanks for the reply.  The walls are basically standard construction.  I used the Roxol mineral wool in place of fiberglass standard insulation, as well as 1"1/2 foam board which was placed in first, then mineral wool. The wall studs are 2x6. 

After the mineral wool, there is poly tarp, then a wall board.

On the exterior, all that is there after 15/16" OSB Sheathing, is the Everbilt Tyvek house wrap.  On the south Side I put up some cheap thin plyboard I picked up at Menards for $11 a sheet.  I did this because there was a leak one day after a strong south rain came and it appeared to have come through a gap in the Sheathing.  Nevertheless, I did not see this leak anymore after I put up the "siding" on the south side.
That wall is pretty sealed now.  I was llsnning to do this method of siding around the whole house, but now I question it's breathability. 

I am now planning to put up cedar shake shingles on the south side. Because of the many nail holes into Sheathing, I'm hoping it will allow more breathability there. 

On the rest of the house, I am thinking to buy a little bit more durable plyboard and cut it into wide strips, paint them and then use them for board and baton style siding. 

I have definitely been taking in moisture through the floor near the front of the house.  I'll be getting it more off of the ground soon and on a proper foundation. 

Also ill be installing a vented propane heater soon and winter is coming and the air is drying out.  My main obstacle is summer as it's very humid wet air here, especially if there's much rain. 

I'm just glad the air is drying up.  Ive noticed the air quality had been a little better recently since the weather is better and I've been running a heater at night.   Im planning on being off grid, so Im trying to do without an AC in the dummer time if at all possible.  This summer it wasn't too bad.  I get good breezes coming through the windows.
Hi Nick,

Your welcome!  Thank you for the additional information.  Based what you've described, I don't think you have to worry about your walls breathing.  You've got you poly vapor barrier where it belongs, on the warm side of the wall.  I'm ASSuming that you didn't caulk your exterior sheathing to your framing, so you should have some modest air movement from the Tyvek to the vapor barrier, which is what you want.  You only have a small living space to worry about.  Your vapor barrier should keep things good and tight and controllable.  If you're feeling like things are getting a bit stuffy, you'll be much better off cracking a window than slicing your poly.  The interior wall cavity should be able to breathe just fine based on the info you gave me.

Now, for the leak on the south (blue?) wall.  Looking at your photos, the only constructive criticism I can offer is that it appears that you may have been a bit inconsistent on the amount of overlap on your Tyvek seams.  Now I need to tell you that I'm not any kind of engineer or authority whatsoever, but In my opinion based on experience, this is not something you should worry about once your house is cladded (note that there was no more leaking after you installed the exterior plywood).

When there is a heavy / severe and especially wind driven rain event, all kinds of freaky weird shit can happen and sometimes, what seems like common sense can fly out the window!  If you combine capillary action and a pressure differential cause by wind, a surprising amount of water can travel against gravity and get into places that seem to be impossible.  This is why when windows are commercially water tested, (basically sprayed with water following some guidelines) the testing often includes building a sealed cavity on the interior side of the windows and applying a vacuum.

Even if you were super careful taping your Tyvek seams, I bet if you look closely you'll find little gaps and failures in adhesion here and there (again, nothing to panic over, but feel free to add some tape where necessary).  I think it's a safe bet that one of those failures, or perhaps a little damaged section in the Tyvek is to blame for your leak that only appeared during wind driven rain (especially since it happened below the drip edge of your roof and you don't have gutters).  I think you'll be fine with any building exterior as long as the material you choose can stand up to the weather where you are.  I wouldn't get hung up on how many nail holes you're going to make in the Tyvek / sheathing.

Can you be more specific about the moisture you're getting through the floor?


P.S. Kudos for building your own tiny home!

I don't want to distract from the discussion of your problem, but if it works into the discussion can someone address:
I have always known as a "fact" that poly sheeting was the wrong thing to do -  that it would trap moisture and cause the problems you're talking about.  Is this not true if installed like has been done here?  (I'm prepared to have another bit of knowledge overturned)
Thank you CJ.  Sorry for late response.  The floor moisture seemed to come after a storm on the south east side which I have poly sheeting under the house and the water tends to collect under there.  Some one told me to simply dig a small trench on the side to divert the rain water. 
Any ideas welcome.  I'm planning to build a new foundation with block and move the cabin onto it. 

I really don't like to see any poly sheeting inside a house.   The only place I've used plastic sheeting is under a basement slab where I REALLY don't want any moisture coming through the concrete.
In those cases, I've used 6mil plastic.

I've noticed that any scraps of plastic laid about or disposed of on a jobsite seemed to attract moisture (I know that isn't exactly accurate, plastic is simply a barrier to moisture movement).  It doesn't matter where it happens to be, one side or the other is wet.   Whether on the ground or in a dumpster, one side is wet.  The same phenomena happens inside a house.   I've had a few 'experts' tell me not to worry, but I really don't like moldy corners or damp-feeling houses.

I've never built in an arid location, so I can't claim any universal expertise.   My remarks may not be valid in those locations.

In the design phase of a house we usually tried to get any rainfall to land as far away from the house as possible...  meaning larger overhangs, lots of good clean drainage stone around the foundation, and sloping the earth away from the house will help. 

The use of plastic sheeting inside a living space always seemed to be a short-term solution used by owners who flipped the house very quickly or shoddy contractors who skeedaddled  ASAP.   I don't recommend it.

Wink, wink, nudge, nudge, say no more ... richsoil.com/wd-gardening.jsp

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