I am renovating a 100 year old cabin with round logs. Eventually I want to put in geothermal HVAC, but I could not even complete a blower door test to size the system because there are so many leaks right now. I am trying to tighten up the structure as much as I can so I can get a good test.

The Kitchen has been stripped bare. We are framing in the walls in preparation for adding the cabinets, so virtually all the logs will be covered. One option will be to fill the cavity between the logs and cabinets with a foam insulation. I was initially looking at Icynene and Airkete as environmentally friendly products, although the size of the job may force me to fall back to some do-it-yourself product like Tiger Foam.

I've gotten some response from people who are interested in log cabins, and they say I should just rely upon chinking to deal with the air filtration. They prefer not to insulate at all, it seems. I can understand why they might be reluctant to spray foam on the logs, but I'm not sure why one wouldn't want to increase the R-Value by putting in at least some insulation.

Any opinions out there? Is using foam an acceptable option for a log house? Would it be better to stay with a loose-fill, board, batts, or similar insulation? Or go pioneer and just settle for the chinking?

Thanks for any insights!

John

Anytime you insulate on the inside, you are asking for moisture problems. Any problems in your vapour barrier and moisture will settle on the now cold side of the log facing inside, between the foam and the log. Rot will start. How to insulate the outside of a log home while keeping it looking like logs? But getting a vapour barrier that works may be a problem. I don't know the shape of the logs - or how wet the your state/area is.

You might want to have heated floors and a woodstove. Perhaps less air leakage if less air is moving around?

Another idea: Insulate, vapour barrier / wind barrier on the internal wall as per a new home, then make it so that there are lots of holes, etc in the chinking, so that the logs in the walled areas have enough circulation to stop rot? Ie from the outside, Log/tyvek/insulation/vapour barrier/wallboard or wood, etc..

Or viewing the logs as insulation, you want unsealed chinking on the outside, and sealing everything up on the inside to form a vapour barrier.

I think having a high density foam (not Icynene which is low density) sprayed on the logs would work well there, although I don't know what the effects of log expansion/contraction may do.. Any moisture getting to the logs should dry to the outside unless you add a vapor impermiable barrier on the outside.

from Building Science Corp:
Vapor Control: High density (2.0 pcf) foam forms a vapor control layer reducing vapor movement through the enclosure, minimizing the potential for wintertime vapor condensation and summertime inward vapor drive. Low density foam allows moisture vapor movement through the foam so other methods of vapor control such as poly, kraft paper, or vapor barrier paint may be required based on the geographic location.(http://www.buildingscience.com/documents/information-sheets/high-r-value-wall-assemblies/high-r-wall-08-spray-foam-wall-construction/?searchterm=moisture through drywall)

John,
A couple questions,
1. Where are you located?
2. How large are your logs?
3. How are you rechinking the logs?
These variables will help a lot in determining a reasonable solution.

A 100 year old log home? CHINK IT! Finish that interior with some non VOC stain (Soy based?)That's a piece of history. Of course, Wes' questions were more on target, and less emotional than were my comments, (I'm not even a "Log Guy" our idea of a log home is with SIP walls, and some kind of log siding outside and, sometimes, inside, SIp Roof over exposed T & TG Decking, etc. I suppose that you'd call that a "pseudo" or "faux" log home. BTW how's your Roof insulation? Windows?

Good luck, post some photos

Wes, in answer to your questions:

1. Where are you located? Richmond, Virginia
2. How large are your logs? I'm not at the cabin right now to measure, but I'm guessing 8-10""
3. How are you rechinking the logs? Good question. I have been using Charles McRaven as my touchstone. He did some initial consulting for me. He typically uses a Portland cement and lime mix, which is what he was recommending in his 2005 book. I have a message in to him now to ask if that is still his preference. I know that many log house people are using newer products, such as Perma-Chink.

Sipper, the roof is peaked, so there is no attic. An earlier renovation by my mother-in-law put insulation directly on the roof under the shingles. I think it is one inch foam board. I will probably end up redoing the roof some day, but not in the near future. (Some parts of the roof are being raised and rebuilt, so that part will have a more modern insulation. And then there is the master bedroom addition, which I hope to do with a vegetative roof if the money holds out.) All of the windows are being replaced with double paned -- probably Lincoln wood exterior.

I'm not sure how to post pictures in this reply, but you can see more than you would ever want at my blog (http://condemnationplantation.blogspot.com/). The left panel has links to photos from different stages of the renovation. The March 1 post has some pictures of the room I am working with now, while there are a few more in the Renovation 2010 picture gallery.

Thanks to everyone who has taken the time to respond.

John

So, I just took a quick tour of your website, I think that we need more pictures in order to get a handle on things so that we can advise you as to how to best proceed .....yeah right! It looks like you'll be able to write the new "How to restore a log home" book when you're done. Pretty neat! but PLEASE don't cover any more of those logs than you have to, there are enough 2 x stud and sheetrock walls in this world. ( And, to the surprise of many who regularly participate on these forums, I wouldn't even want to cover those walls with SIPs) The day will come when most of this will be gone, you're preserving a bit oh history.

BTW Davy Crockett and Daniel Boone both "rocked" really, they not only used logs to build homes they also used rocks (or technically, "stones") Look it up!

Heh -- sorry for the overkill on the pictures. I just can't help myself. What is interesting about the cabin is that it is in the city limits, and it is only one among a dozen or so in the area. My daughter owns one next door to this one (and it is in much better shape). Most of the structures seem to have been built as hunting or fishing cabins near the James River when the city was still miles away. Now they are surrounded by more conventional looking houses as the city expanded its borders and suburbs grew up. It is too bad I have a day job, or I could spend more time working on it.

John

John,
I suggest that before you build your stud walls in the kitchen area, complete the log renovation, especially the chinking. Then build your walls with no insulation.
Here is my reasoning:
1. The logs, if solid and properly chinked, should provide a stable, comfortable living space in your climate.
2. The kitchen area will be only a small portion of the exterior walls. So the added insulation will have little effect on the energy needs of the whole house.
3. The log walls move as a unit based on temperature and humidity differentials between interior and exterior.
Adding insulation to this area could change these differentials in this area of the walls. The logs in this area could reacte differently from the rest of the house, causing stress cracks in the chinking and even the logs themselves.
In conclusion, I think you would be better off leaving out the added insulation.

Log houses endure because thermal mass compensates for their lack of R value. http://www.loghomes.org/uploads/The%20Energy%20Performance%20of%20Log%20Homes1.PDF
The Cliff Notes: You have many more tons of wood than you would find a stud wall house. That mass captures heat during the day and carries it over into the evening. By buffering daily highs and lows, your walls are more efficient than stud walls when the average daily temperature is 70ish, which would be a fair chunk of fall and spring in Va. Adding insulation on the inside would save energy in winter and summer, but you'd give much of it back in fall and spring by cutting off the home from this mass effect. Ideally, you'd add insulation to the outside of a high mass house, but covering your home would be a crime.
Cram as much insulation as you can into the foundation and attic. Leave the walls alone.

Hi John, keep up the good work! I also live in a historic log cabin (have lived here for about 20 years) and I found, like the other log enthusiasts you've spoken to, that my main problem was air infiltration. Sealing gaps and replacing old, single-pane windows both made a large difference. I'd consider Perma-Chink if I were you. It expands and contracts, so it maintains a tight fit, unlike the cementitious products, which will crack and leak air (and water) within a few seasons. You can use some blue board in the middle of your chinking gaps, sandwiched by Perma-Chink on the inside and outside. It takes a lot of custom cutting of board, but ups your R value at your weakest points, and reduces the amount of Perma-Chink, which can get expensive. Cheers. Will

In Richmond, VA foaming the interior of a log house isn't such a hot idea, since it puts a vapor retarder on a structure than needs to dry both toward the interior & exterior. It's a mixed climate with a modest ~4000 heating degree days, 1350 cooling degree days, but it has high summertime humidity and needs to dry to both the interior and exterior to keep the logs stable.

After chinking with the best products you can find, an interior studwall insulated with dense-packed cellulose (and no vapor retarders or vapor retardent interior finishes) would work. Cellulose would wick moisture away from the logs rather than trapping it there the way closed cell foam would. Use "borate only" fire retardents (all wet-spray cellulose products are borate-only, and can be dry-blown), as the borates will also cut the termite risk. The only condensation risk periods would be on the colder days of January, and fairly short-lived, not for weeks on end the way it is in colder climates. Vapor retarders here would cause more problems than they solved, and the hygric buffering of a cellulose wall would be a humidity stabilizer. (And it adds some thermal mass to the already massive wall too.)

John,

Just looked at the photos of your "labor of love"! Quite the project! I do have one comment after seeing the existing chinking: use the McRaven suggestion of cement/lime as the space to be chinked is so large. It would cost a bundle to chink that much with any commercial chinking available (Perma-Chink is probably the best one available).

You might want to call Perma-Chink and ask their advice on what to do - perhaps covering the cement/lime chinking with Perma-Chink to enable it to weather better. If you want to purchase any Perma-Chink or log stains send me a PM and I will give you the name and phone for an excellent distributor in Charlotte who carries the top manufacturers of those products.

Best of building to you!
richm

Well, looks like this thread is closed but I'd like to reopen it (if anyone cares to) because I'm trying to do something similar but with different parameters and I'd like to hear from others if what I'm doing is a mistake or not.

We have a log house as well and will be doing some fairly heavy renovations, including redoing the roof (not just re-shingling it, but ripping the plywood layer, foaming the exposed space, then re-plywood and shingles).

Unlike the other gentleman, ours is NOT a historic house: it's 40 years old and was not built particularly well. We've spent the last 12 years fixing all the "little things."

Also, we live in upstate NY where it gets cold in the winter but it can also get very hot & humid in the summer.

Another difference: both my wife and I live and work from our home so cold weather in the winter is a big problem.

We also are considering spray foaming 2 inside walls of the house with spray foam and then framing on top of that with light-colored wood strips for a nice wall finish.

Reading all your posts (a few months old by now) I'm torn. Some of you think any spray foam (esp. closed cell) would be a VERY bad idea since it might trap water/condensation between the inside of the logs and the foam and create a rot situation. Also, we'd lose that very effective wood-mass of the walls for temperature control.

On the other hand, I'm also reading that if using the proper foam (i.e. cellulose, borate-based: can this be sprayed on walls effectively?) with no vapor barrier it can control humidity AND insulate a very imperfect wall from the inside.

Not sure where to go from here.

Any opinions?

A confused log-home owner.

I'm working on two log homes; one 30 years old, one new, both thermal disasters. First step is to decide if you want the log look on the inside or outside. You've decided outside so you're going to cover up the interior of the logs. Are you saying you're going to leave the other walls as logs (other than the two you're insulating)? Foaming the walls with an open cell foam like Icynene should not trap moisture, but consider using cellulose as the cost should be less, it will work on uneven walls and it has some ability to absorb some moisture. Others have said here that a closed cell foam might trap moisture but it seems to me that the permeable logs would allow the wall to dry toward the outside. NOTE: leave a gap between the new interior 2xs and the logs to maintain a thermal break. Also seen on this thread and in log home sales literature is the notion that log homes have a thermal mass benefit. That may work somewhat in practice and may work well in a laboratory, but wood moves! Chinking is inexact; caulking will work until the wood moves; you inveriably end up with lots of infiltration which keeps the furnace running. On your roof, spraying the outside of the roof boards should work fine; just keep in mind that once you have overcome the infiltration problem (probably your biggest source of heat loss right now) you need to look at the total R value of the assembly. The higher the R value, the less heat you'll use. So depending on how much depth you have avilable you may want to increase that space so you can increase the R value. If you are doing all that work, now is the time.

The vapor permeance of closed-cell spray polyurethane foam is roughly that of the wood itself, but the R value at any given thickness is about 6x that of the log. Applying a couple of inches ccSPF to the inside won't dramatically change the drying capacity of the wood toward the interior during the summer season, but would lower the temp of the wood to below the dew point of the interior space air in winter, causing a slow winter-seasonal accumulation of moisture in the (an accumulation that is probably already happening a couple or three inches into the log, but would now be closer to the ccSPF/wood interface.) The seasonal hygroscopic dimensional changes of the log may not be compatible with the fairly rigid SPF though- I'd want to hear from somebody who has actually done it before moving forward on that. If it's going to be foam-insulated on the interior, closed cell would be a better choice than open cell though.

Cellulose (sprayed or blown) will have more mechanical compliance/pliability to the seasonal changes, but it could be tough to air-seal it sufficiently enough to keep it fully dry if you're only doing a couple of walls. You'd want to limit the vapor permeability of the interior somewhat with latex, and keep it very air tight, but you'd never want to use an interior vapor retarder, and you'd for SURE have to use some sort of non-wicking sealer on the chinking to guarantee that it does soak up the morning dew.

In general, and in this particular, it's better to put the insulation on the exterior of the structural wood, which keeps the wood above the dew point temp of the interior air. That would also give you the max benefit of the (very substantial) thermal mass characteristics of all of that cellulose & lignin of the logs themselves.

With any house, fixing the air leaks is the single most cost effective thing to do, and with a log home may be an annual maintenance issue. Logs change dimension shift around a lot with humidity & temp, and unless all seals are flexible, with good adhesion leaks are guaranteed to develop over time even after a thorough round of air-sealing. A foot-thick log may be only R10-R12, but with it's thermal mass could have the energy-use equivalence of an R12 insulated concrete form (which is closer to an R19 studwal) but ONLY if you can keep it air-tight.

It occurs to me that the chinking being the lowest-R thermal bridge, spraying over the interior chinking with an inch or two of ccSPF could make a very significant improvement in thermal performance without changing the drying characteristics of the logs at all. But again, no experience here, just thinking while typing...

I'm definitely keeping the log look on the outside so insulation is strictly from the inside (if I go that route). The way this house is built, I only need to insulate those 2 walls because the other 2 walls (completing the house on that wing) are going to be closed in by the new addition we're adding. The addition will be conventional framing for cost/labor reasons but will be sided with log facia/veneer which looks extremely close to what we already have (from old collected logs from a company that specializes in the type of home I have: Vermont Log Homes, now defunct) Cost is a big factor (of course) but I'm less worried about costs than I am about ruining the house long term because of mold or other problems. I was told open cell foam can "wick" moisture and possibly create that long term damage. But I also never of that in context with log homes where drying can/should occur from both sides of the log. So far, I'd only considered the same closed-cell foam I was going to use on the new roof. Could you please clarify for me what you mean by "leave a gap between the new interior 2xs and the logs." Do you mean a space between the new interior wall (that will sit on those 2x4s) and the sprayed foam on the inside logs? Also, I had not (until now) considered seasonal wood motion that may negatively affect sprayed foam which hardens and may not lend itself to the application I have in mind. Hmmm..... No chinking in our house. Logs are next to each other, from a 1969 kit from Vermont Log Homes. And I agree with increasing the "R-Space." We're trying to decide (assuming we're going through with this process) how wide that interior space (i.e. the space between the interior of the logs and the interior of the newly interior wall) should be. Say 3 inches. Plus, if I understood you correctly, a little more for an air break, right? We do have a fair amount of space available for this strategy: any recommendations for minimum space?

You said "causing a slow winter-seasonal accumulation of moisture in the (an accumulation that is probably already happening a couple or three inches into the log, but would now be closer to the ccSPF/wood interface.)" That's the part I'm very concerned with. As for getting in touch with someone who's done this, that's what I'm hoping and why I joined this thread. There seems to be very little other information on the Internet about the strategy we're discussing here. Perhaps because it's a no-no? As for keeping a good air-seal for humidity control (to prevent it from reaching the cellulose), in our case this would be difficult on many levels, including the fact that the finished interior wall is likely to be wood planks of sorts. So perhaps that removes the option of cellulose as the insulation agent. As for insulating from the exterior, I agree that with the benefits from an engineering perspective but it's a non-starter for us since the idea is to preserve the log home look of our house, especially from the outside (some inside wall logs will get covered in the renovation (and only for insulation purposes) but we'll still have a lot left to look at). As for fixing air leaks, that's a non-issue for us. Non-issue as in Yes, we're absolutely going to be doing it. However, I'm not sure that will significantly lower the heating bills. While the house has many problems, overt air leaks are (surprisingly) not one of them. Go figure! Our logs are not 12 inches, unfortunately. 6 to 8 inches max, everywhere. And this house does not have any ching: logs sit on logs, kit-fashion (from an older Vermont Log Home kit). Freddy.

I went to your site but couldn't figure out (from your posts) what solution you went with for your log house. COuld you let me know? I'm considering a similar approach (spray foam the inside of logs in our house for insulation) and I'm trying to understand the implications of this strategy. Freddy.

Freddy,

We haven't quite gotten there yet, since our kitchen cabinets are only now being constructed. We decided to be conservative. We will be chinking everything as well as we can behind the cabinets, then stuff the gaps with something like Dow's SafeTouch insulation. There really isn't going to be much space, since the cabinets are going to butt pretty tightly up against the logs. We will also probably then seal the gaps at the top with a spray foam where the cabinets touch the ceiling to keep out drafts and critters. We are leaving the interior logs exposed wherever we can elsewhere in the house, hoping to seal things with the chinking as best we can then rely upon our efficient HVAC systems and the thermal properties of the logs to do the rest. We will still have plenty of conventional framed walls where we are doing new construction or replacing failed walls.

Good luck on your project. I often feel like I am throwing darts in the dark with this stuff.

John