"leave a gap between the new interior 2xs and the logs": the 2x4's shouldn't be touching the logs. They could be an inch away or several inches. The more depth you have for insulation, the less heat you'll need in the house. (All other things being equal). It may be worth considering a layer of 3/8" drywall (taped) on the living area side of the studs under the boards as an air barrier.

"keeping a good air-seal for humidity control to prevent it from reaching the cellulose". Dense pack cellulose will form a good air barrier by itself, but the more air you can keep from reaching it the better the air seal will be; hence the suggestion for a layer of drywall.

"air leaks, that's a non-issue" Have you had a blower door test? Thats is the ONLY way to tell if it is an issue or not. If so, what were the results? If not, you should have one now and one when you are done.

I haven't posted any results from the log home work we've done. In one case we added onto an old log home but most ofthe house is still logs inside and out. We did foam the sills, tighten some windows and install SF above some of the roof boards but we're able to do much more than that. In the other case - a new mountaintop house with constant high winds - we're trying to minimize the windwashing of the fibergalss insulation installed over the ceiling boards. I think the ultimate solution is to reinsuate the roof but that will be expensive and won't happen this year.

With no chinking and a caulked interface, a highly-permeable housewrap like R-Wrap or Tyvek would still likely improve the air-leakage.

Dense-pack cellulose will certainly be "good enough" as an air barrier in terms of thermal-loss via convection, but isn't quite guaranteed to be adequate from a moisture-transport & accumulation point of view without help. The more air-barriers & sealing the better, as long as they're water vapor permeable (no foil, poly, vinyl allowed.) Cellulose will buffer quite a bit of moisture without damage though, and as long as it can dry toward the interior all spring/summer/fall a 3-5" layer of dense-pack may be enough. Drying toward the exterior through the logs would take more months than you get in a year- use nothing more vapor retardent than standard latex on the inteior walls, and use a (vapor permeable) sealer on the exterior of the logs to prevent wicking of dew/rain into the wood.

Bob I's concept of leaving a gap between the studwall and logs and dense-packing it with cellulose is absolutely sound. That would provide a thermal break for the studs, and allow some mechanical freedom for the logs, reducing the amount of air-leak-creating mechanical stresses that it would otherwise undergo over several seasons. Since the studwall isn't structural, using 2x3s would increase the amount of thermal break, greatly enhancing thermal performance. If you set the interior face of the studs to 5" from the logs and dense-packed it to 3-3.5lbs/cubic foot you'd be adding ~ R19 to the total stackup. If you only went 3.5" (the same as if you'd butted 2x4s against the logs you'd be looking at only ~R12 since you'd have less insulation between 2x3 stud edges and the logs.

Closed cell SPF is highly hydrophobic- it absolutely will NOT wick water, even though it has a modest permeability to water vapor. A flash 1" seal of the interior of the logs would likely be flexible enough to not separate over time and would form a good air-barrier, adding ~R6 to the stackup. But it's a lot more expensive than a sheet of Tyvek (sealed at the edges & around openings) and adding 1/2-3/4" to the thickness of the cellulose achieve similar R & air-tightness.

[edited to add] If you're insisting on plank interior, a vapor-permeable housewrap between the studs & planking could help here too. [end edit]

Bob- I'd be very interested to read more about what you've done with log homes (my brother recently moved into one in WA and is slowly dealing with all of it's issues.)

I have not had my house "blower tested." Not sure how I'd go about that (or if anyone does that around here). Where do I go to find out more about this? Construction companies? Also, when you say "cellulose" do you mean "wet-spray" cellulose? And do you "spray" that between the exterior side of the 2x4? (between them and the interior of the logs) And if so, that means the celluloase contacts with the logs, right? But wouldn't that make the cellulose more suceptible to wetness from the outside (e.g. via condensation or even openings)?

Wow, so much to understand...

Someone earlier said he was throwing darts at a board: you're way ahead of me! I'm still looking for the board and I don't even have the darts!!!

Anyway, based on everyone's feedback so far, I'm taking a step back and considering a slightly different approach (presented below for your opinions).

Approach B: with the continuing intent of insulating the house from the inside, and still willing to cover the applicable interior walls, and still thinking in terms of some form of Extruded Poly Foam, BUT allowing for "NO CONTACT" between said foam and logs, and allowing an air space between interior of logs and insulating layer (for breathbility), So, HOW ABOUT...

Framing 2x4 away from the logs (no contact) on which to hang the new interior finished wood wall, but right on the other side of these 2x4s attach rigid foam panels (e.g. 3" Atlas roofing panels, foil-backed with R-19 value). Those boards can be attached directly to the 2x4s with perhaps 1" space between them and the interior of the logs to create that air space.

I get all the advantages of the Sprayed Foam Insulation solution with none of the mold issues (of which I am now very nervous about). Plus that way, I can create a very tight seal between the logs and the interior of the house (e.g. by gluing the rigid foam boards tightly together).

Opinions?

When we talk about "breathability", we're talking about WATER VAPOR movement through the material, not free flow of air. Moving air transports far more moisture than vapor diffusion through ANY type of wall material, and is a far greater mold hazard than mere high-vapor permeance. If you're going to leave air gaps, you have to be religious about blocking any possibility of convection currents from the interior into that space, where it will condense/frost on the logs all winter long. In masonry walls cavites are used to keep water from wicking through the porouse masonry into the wood structures, but those are vented to the exterior top & bottom to purge moisture from the cavity to prevent mold on the wood facing the cavity. That approach isn't going to work so hot in a log structure.

The whole point of sealing the log with a wood-sealer on the exterior and putting a vapor permeable (but air-tight) housewrap on the INTERIOR of the logs is to minimize the uptake of moisture into the wood or cellulose from the exterior, and reduce the air-infiltration driving forced from pushing humid conditioned space air into the wall cavity you're creating.

Doing the full R with slabs of sealed UNfaced EPS works up to about R15 (4") but make it tight & sealed to both sides or you run the risk of allowing convection loops. Over 4" thick it becomes too vapor retardent for the logs to be able to dry toward the interior in a reasonable amount of time.

With foil-faced iso you have zero capacity for drying the logs toward the interior, and any moisture that ever found it's way in there wouldn't have enough months in a summer to dry to the exterior (maybe if they made summer 15-20 months long it would work! :-) ) If the iso were going on the exterior that would work in your climate zone though. Some fiber-faced iso roofing panels are permeable enough, but look at the specs carefully. It needs to be at least 0.5 perms. Many just specify "less than 1 perm" on the generic spec sheets, and it may take a few phone calls to get the real number. Any fiber-faced version would be preferable to a foil or poly facer though. The iso itself is fairly permeable- it's the facer that determines the rating of the panel. (I used some recycled fiber-faced iso rated at about 5 perms to insulate the interior of my poured concrete foundation walls- took some digging to find the spec.) The industry trend has been toward lower & lower perms though- some fiber faced goods are about as low-perm as foil facers at about 0.02 perms- be sure to avoid those.

Dense-packed cellulose can be either wet or dry blown, but instead of sprayed with a gun, a hose is inserted into the cavity and it's injected until the blower backs up , pulled back a bit, until the blower backs up, repeat until the cavity is full. It ends up using 50%+ more material than standing back & wet-spraying it gun-style, but DRAMATICALLY decreases the amount of air that can move through. Wet spraying it any deeper than 3.5" in a log house you'd want to let it dry for at least a WEEK before closing it in though (and even at 3.5" you'd want to give at least 3 days), since the logs inhibit drying to the exterior. Dry-blow this one dense-packed behind a "blow in bag" or "blow in blanket" type screening.

If you're not going to put up a latex-painted gypsum layer under the planking, using fan-fold 1/4" or 3/8" XPS siding underlayment under the paneling as an interior air-barrier & vapor retarder would have about the same vapor retardency as a latex-painted wall, enough to keep the cellulose from taking on too much water in winter, but allowing plenty of vapor breathability to dry during the spring/summer. It would add about another R1 to the stackup too, but it's the modest vapor retardency & air barrier aspects that you are after here. Foam or mastic seal any seams/edges/penetrations before putting up the planking. IIRC planking needs to be at least 3/4" thick(?) to meet code as an ignition barrier for the XPS.

Cellulose will be more protective of the logs from mold than ccSPF, since it absorbs & releases moisture without damage. SPF can be protective, since it condensation on it's surface isn't damaging, and it blocks air, but at 2" (r12) or more the ability for the log to dry in that direction is dramatically reduced, whereas drying through R12 of dense-packed or wet sprayed cellulose in less than one season is pretty much guaranteed.

I like the idea of using Tyvek on the inside of the logs. Maybe that would work on the interior of the 2x4's also. It does need to be well sealed - meaning tape all seams etc.

I don't know what everyone else can find for 2x3's but whenever I see them they are only usefull for making rocking chairs or framing curved walls.

Blower door testing - google Energy auditors NY or upstate NY or similar. Same with dense pack cellulose. My insulation contractor gets his cellulose from National Fiber in western Mass; they could give you contractors in your area & possibly leads for energy auditors also. Some of the better insulation companies have the training & certification to do their own blower door tests.

What I've found with log homes so far is: the logs leak air; the roof boards also leak air; the joints between the walls and roof also leak air. Sometimes the exposed roof boards are covered with 2x's & fiberglass making re-do's complicated & expensive. Some log cabins (and at least the older Timberpegs) have layers(s) of foam sheets above the ceiling boards which are rarely sealed around the edges allowing air leakage. Overall the builders of these (as well as the majority of builders) have been clueless about air sealing; the problem is that in a log cabin you are limited (at the walls) to one layer, and board ceilings, so easy "fixes" like Tyvek are impossible. It's love to build one or do a major energy retrofit so that I could identify how energy efficient they are "can" be.

In these, as in every other house, one of the first things everyone should do is foam the sill area, from the concrete foundation to the subfloor. This will stop an amazing amount of air leakage and give you warmer floors.

Finger jointed 2x3s are pretty good, if you can find 'em. Some of the other kind are useful for pulling corks, if you sharpen one end. :-)

Excellent point about air sealing the foundation sill (probably the #1 most overlooked major air leak in most homes.) Depending on foundation type it may be reasonble to retro-fit insulation in there too. (My brother retrofitted R10 XPS in the poured concreted crawlspace with rat-slab under his log home.)

Hello! I would like to continue this thread or start a new one about proper log cabin interior sealing, etc.

I have purchased a cabin built in 1999 in western NC, it sits at 3200' near the NC and Tenn. line. This home is made out of white pine 6 x 8" square logs, with a milled groove pattern ( so they fit on top of each other). No chinking just calk. May have a gasket of some sort between the grooved area ( not sure on that).  

I have been like many others looking to understand how to seal out air and not trap mold (Moisture) . 

We have raw logs on the extierior walls and have removed all the old cheap panneling from the partition walls. Now we need to cover the inside of the log walls with a new wood to get the look and feel we want.

I plan to calk the outside with a Perma-Chink  type calk and then do the same on the inside with a flexable calk. I then plan to cover the inside walls with 8" T&G v-groove or Beaded. This 8" board needs a finish , and I prefer a white wash on the White Pine board or just clear coat. 
The questions I have are:
        
         1. What will be a low or no voc finish that will also not be a vapor retarder? As I understand I don't need to stop the homes ability to breathe but I do need to stop the flow of air, while trying to have a nice finish on the inside.
I like a semi gloss or gloss look on the new wood. Any thoughts on that , and finish products that I could consider would be a great help.

         2. The homes ceiling and roof are as follows; The ceiling is Vaulted Truss 3' peak crawl space,  6" t&g V-groove with blown in insulation that looks to be glass, not cellulose, or paper. There are no roll batt or paper between the insulation and the top of the T & G in the ceiling.
The roof is 3' metal and lath 1x4 hardwood screwed to the top of the trusses. No sheeting.  
Qusetion ; What needs to be done to help this home prevent moisture buildup and yet be as efficient to heat and cool as possible?

Dana1; If your around I would like to hear from you as I have been impressed with you answers. Anyone else please reply as you feel like.

Thanks for any help,
 Cuz

Since you mention Perma-Chink, give their office in Knoxville a call.
They have a full line of products designed to work specifically with logs, and wood in general.
Their products are good and their advice is sound.

Hey Thanks Wes, I'll give them a call.

I found Timber soy stain by eco safe products. Anyone on here ever used their products? They also have a no VOC Clear finish, for wood floors. Trying to keep down on vapor and chemicals.
Cuz