So its two questions, but may or may not be related. First off, a little info. I live in NC mtns, very rainy area, sometimes 100+ inches a year. Moderate temps, a good bit of heat used in the winter, and a little ac in the summer. I just bought a home, and am in the process of renovating, and adding on. Humidity tends to run high here and many homes have moisture problems. The house is currently in great condition, but you can tell there has been lots of moisture in the crawlspace. It does have a 6mil vapor barrier covering the dirt, its not perfect, but much better than many I have seen. My plan was to cover over this plastic with another layer, but it will run up the cmu walls. I would use window flashing membrane at the top along with a 1x2 strip, attached to the sill plate, to basically encapsulate the crawlspace. I will also add a dedicated dehumidifier. I have heard both ways on this, some agree some do not. I have also heard, if I do this I need to remove the insulation from the floor. Second, as part of my renovating, I will be adding lots of reclaimed wood to the interior walls and ceiling. Ideally I would like to put black plastic behind the wood, as there will be lots of cracks, holes, etc. I know in a warmer climate, this would be a no-no, and a colder climate, it would be expected. I can also say that I have worked on many homes around here, and most do have a vapor barrier on the inside of the wall. Local code does not require it though, and I don't think it will cause any issues, except it may lower my infiltration rate to the point of needing an hrv. I also should add living in this area, I usually have a dehumidifier in the house, and monitor the humidity level regularly. I think between the 2, I will cut out most moisture coming into(and under) the house, and also help my heat losses. Any thoughts? Those against, those for, and why? Thanks

You may need to leave a termite inspection strip at the top of the CMU foundation depending on how common termites are iin your area. If you fix clamp the vapor barrier to the CMU with a strip of 1x furring through -screwed to the CMU with TapCons and leave the top couple of inches free you would have that inspection strip.

You can leave any pre-existing floor insulation in place, but you should also insulate the CMU walls to something like the current IRC code-min of R10. This is most easily done with 1.5" thick fire-rated Thermax rigid polyiso, clamped to the wall with 1x furring, which at the top could be the same furring clamping your vapor barrier in place. Using fire-rated Thermax usually means you don't need a thermal barrier against ignition, and it's definitely safer to leave exposed than polystyrene (XPS or EPS), which have a lower kindling temp and melts while burning spreading the flame, whereas polyiso chars in place. The termite inspection strip can then be insulated with carefully sculpted R15 high density batts (fiberglass or rock wool), which can be easily removed & replaced for inspection. You can insulate the band joist and foundation sill with trimmed batts too, but seal every joist, subfloor, and sill plate seam with a bead of can-foam first.

Ideally you'd have a metal capillary break & termite barrier underneath the foundation sill, and you'll have to figure out a way to air-seal the sill to the foundation in a termite-inspectable fashion if that's a risk in your area. Otherwise cut'n'cobbled polyiso can-foamed into place works pretty well for sealing and insulating any bit of CMU ledge, and over the top of the foundation sill.

Generally speaking vented crawlspaces bring more moisture into the house than it purges in an NC climate, so you're on the right track with this.

I'm not quite sure what you meant by:

"Second, as part of my renovating, I will be adding lots of reclaimed wood to the interior walls and ceiling. Ideally I would like to put black plastic behind the wood, as there will be lots of cracks, holes, etc. I know in a warmer climate, this would be a no-no, and a colder climate, it would be expected."

Is this on the interior side of the above-grade walls, or something else? If it's on an above grade wall that your rehabbing, we'd need to know more about the wall construction and material stackup. Generally speaking adding true vapor barriers such as polyethylene sheeting in above grade walls is something to be avoided if it can be designed out,and it usually can be. Your climate zone (3A or 4A, depending on your ZIP code) is more forgiving that some, but there are plenty of ways to screw it up.

Thank you for your input. I'm not sure on the requirements for termite inspection here, I will check into that. I can tell you in the 20 years I've been working on homes here, I have never found termites in a home. However, every time I make repairs from water infiltration, carpenter ants are always there. It looks as though they have placed flashing inbetween the cmu and sill.

Yes, the plastic will be on the interior side of above grade walls, also the interior side of the truss ceiling. I will be removing the exterior of the walls as well, because I will be changing the window and door openings. The siding is currently t1-11, which means I won't really be able to re-use any of it. There is also what I know as blackboard sheathing on most of the house, and I will likely replace it with plywood while i'm in there. The new exterior walls will consist of 1x interior, 2x4's, 1/2 plywood, tyvek, and 1x board and batten siding. I would be open to using something else behind my wood, but I bought a 20x100 roll of plastic for the crawlspace, and was going to use the extra in the walls. Maybe just use strips of it behind where needed, but that would be a pain. Also a friend of mine said that he heard that felt/tar paper is not recommended inside homes anymore, something about off-gases, but I haven't heard that anywhere else.

Btw I am in climate zone 4. Any other input on either question? Also currently there is r-19 insulation under the subfloor. I have discovered that the foundation walls are about 4' high. On the outside, for 1/2 the perimeter, all but 12" is below grade and has waterproofing, the other half of the house 30" is above grade, and the crawlspace is about 30" as well. Not sure if any of that makes any difference. I eventually plan on digging down to the footer, adding bituthene, and then bringing the out side grade up as high as I can to help with drainage around the house. Of course there is one corner of the foundation that will still be 20" or so inches above grade, and thats where my access will be.

As for the above grade interior walls, I'm not really sure the best route. Most of my searching has found nothing really. Most people are adding reclaimed wood to existing walls and just painting them black. The ceiling is not as big of a concern as it is reclaimed cedar lap siding, and there won't be as many cracks. I could piece in plastic only where it is needed on them. The walls however, will be various size 1x running horizontally, from 5" width all the way to 18". Lots of cracks, knot holes, nail holes, etc. Part of the house will also have a reclaimed pallet wood wainscoting, running vertically to a chair rail. So total wall coverage would make much more sense. Has anyone else heard about problems with felt/tar paper? I haven't really found anything on the web, other than a few people with chemical sensitivities.

Do NOT install plastic layers in your above grade framed walls, since that limits the ability of the walls to dry. Putting in in the ceiling under a vented attic also creates more problems than it solves. In a zone 4 climate vapor impermeable sheet goods have created far more moisture problems in houses than they ever solved. The only place impermeable plastic really belongs is between the dirt and sub-grade foundation and the conditioned space, to limit the groundwater moisture migration into the crawlspace. Many/most "sick building syndrome" houses of the 1980s were aggravated or caused by the improper use of plastic sheeting in walls.

If you need to use broad sheet membrane for air sealing purposes, use Certainteed MemBrain, which is 2-mil nylon, and NOT polyethylene sheeting. It has the property that if the humidity of the air next to it reaches mold-growth levels it become permeable to water vapor, which allows the moisture to leave. When it's dry, it's relatively vapor-impermeable (a Class-II vapor retarder). If you can't find it locally, the big box stores and Menards are now selling it , sometimes only online:

http://www.homedepot.com/p/CertainTeed-MemBrain-100-in-x-50-ft-Air-Barrier-with-Smart-Vapor-Retarder-902018/205920791

http://www.lowes.com/pd_750463-27-902018_0__?productId=999958593

http://www.menards.com/main/b-446267.htm?

Sometimes it's easier to just put up a layer of wallboard under the scavenged wood paneling, painting it with a black latex paint, but MemBrain doesn't hurt, only helps. It's possible to detail wallboard as an air barrier, and painting it with latex paint brings it's vapor permeance down into the Class-III vapor retarder range, which is good enough protection against wintertime moisture build-up in walls for a zone 4 climate.

The black board sheathing is probably CeloTex or other brand of asphalted fiberboard. If it's in good shape, leave it- it adds ~R1-R2 to the whole stackup, and also behaves as "smart" vapor retarder, similar to 2-mil nylon. It's less structural than plywood, but can meet most structural sheathing standards if the nail spacing & type is correct. It's extremely moisture tolerant- it can even be left out in the rain(!) and has a good track record even in walls without #15 felt between it and the siding.

The R19 under the subfloor can stay even after you encapsulate the crawlspace, and it will deliver some thermal performance even after you've insulated the foundation walls.

I'd put some rigid foam on the interior side of exterior walls, tape it well and then add your 1x wood.

Thanks you guys. Almost everything I work on was built in the 80's so that explains alot lol. I probably should have mentioned that the insulation is faced. I'm not as concerned with infiltration as I am with just having a black backer behind the cracks and knot holes. Maybe just spray the insulation facing black lol. Wallboard or rigid foam are not an option for me. The main reason for the reclaimed wood is because I have a very limited budget, its all wood I have reclaimed myself. The existing drywall will all be removed also, as window and door openings and electrical will be changed and all the interior walls are being moved. At this point, I'm really hoping some 15lb felt will be ok. Good to know about the blackboard, although it will probably get removed anyway since so much will be changing with the framing. Its georgia pacific if that makes any type of difference.

A foil facer is potentially a moisture problem on the batts, but if it's asphalted kraft paper it's not.

GP is /was a major manufacturer of asphalted fiberboard sheathing. http://www.buildgp.com/regular-fiberboard-sheathing.

I don't know of any problems with using #15 felt on the interior. It's not exactly an air-barrier, but as long as you install it in vertical strips such that all seams are overlapped and fully supported by the studs to which it's stapled it should do OK. If run horizontally the seams would not be supported where it crosses between stud, and there's no easy way to get a long term air-seal where it can flex.

You could use 1/4" XPS foam for about $.25 per sq ft. It can be taped and spray painted black. Maybe tyvek can be spray painted too. In almost all cases, infiltration IS important for energy, wall moisture and dehumidification cost reasons. I'd keep poly and foil out of the exterior walls (not breathable).

For interior walls (no moisture drive), I'd use black poly (or tyvek if paintable) vs felt (only because, IMO, asphalt fumes are questionable).

Without the full wall stackup being known, black poly isn't a great recommendation.

The 1/4" fan-fold XPS siding underlayment idea can work. It usually has thin facers to bring the vapor permeance down to 0.8-2.0 perms, but that's OK, not a moisture trap. Like felt, locating the seams where fully supported by framing is important for air-tightness. Taping the seams with housewrap tape helps too.

Thanks you guys. The insulation is kraft faced. Good idea on running the felt vertical. I will be caulking as much framing as I can when I have it open, and running a bead of caulk in each joint as the sheathing is applied, so that will cut my infiltration a good bit. I probably will use the plastic on the "dry" interior walls. All of the walls in the house will be 1x or thinner material 2x4 walls. At least until I start running out of reclaimed material, then it will probably have drywall top wainscot bottom. I will have some places, like kitchen backsplash and possibly a shower, with reclaimed 5v metal roofing. I would rather use felt than to have to paint anything else. Although, between that and all the wood, I will have a very flammable house lol.

Plastic should be OK on partition walls, just not exterior walls.

The ~1x planking is not a fire hazard, in fact it qualifies as a thermal barrier against ignition for far more ignitable-spreadable products such as foam insulation and plastic sheeting.