insulating log home exterior

[WillyJohan]

Hi all. I'm looking for advice on insulating the exterior of my log home. Its been pretty warm here in SE BC this winter (or first in the house) but it was around 0 F for a week or so and we used nearly a cord of wood in that time period.

We're going to be reroofing and doing some other upgrades and thought it might be a good time to improve the walls.

I found this guide and was thinking that the approach outlined on page 9 seemed pretty straight forward.

My question is around possibility of setting myself up for condensation issues inside the wall. Does anyone have experience with insulating log homes from the exterior? The diagram has a vapour barrier between the logs and the insulation, does this seem like good idea (keeps warm interior moist air from getting into the insulation) or a bad idea (keeps the moisture that will inevitably get into the wall from being able to dry to the inside)?

We've got interior chinking and roughly 12" to 16" diameter logs making up the wall. Not too sure how much and what type of insulation we'd add to the exterior.

I would really hate to introduce rot to a well functioning home. Also don't want to do anything permanent (eg spray foam the whole exterior) just in case (in case of what i have no idea but you never know what the future holds).

Thanks in advance for any advice.

[barbender]

I think you need to ask yourself why you are living in a log home if you are considering these approaches.

[WillyJohan]

Hi Barbender,

I'm not sure I fully understand your comment. I'm living in a log home because it was the best quality home available that we could afford in in the town where we needed to live to be close to our business. Is there something inherent in the construction that makes external insulation a bad idea?

Thanks for you input.

[doc henderson]

I think it is because you are basically building a house around your log house.  carry on.

[WillyJohan]

Doc H, I guess it could be seen as that, but I'm hoping that the the lack of any real structural requirements in the furring would reduce the cost somewhat. I was hoping I could get away with 24" oc and just using some scrap OSB and 2x2 as a nailer.

I Figure its not much different than the continuous exterior insulation that most energy codes call for in these parts, except that it would be cheaper and perhaps the wall could dry to exterior a little easier.

perhaps I'm underestimating the effort (wouldn't be the first time).

thanks.

[sprucebunny]

As the articles says, the logs will be inside the vapor barrier and theoretically warm and act as mass to even out the heat. Have you priced siding ? How big is your roof overhang ? How will you attach the wall to the overhang ? 

Any moisture in the log walls will be 'drying' to the inside.

[doc henderson]

this was an exceptional cold spell.  is it better to always have an extra cord of wood if needed, or should you build a super insulated structure that is only needed a week or so some winters.  depends on time and materials to do the fix.  I thought big logs insulated themselves.  

[Sod saw]

Hi Willy,   If we knew where you are living, it may help to provide more accurate information. You can fill out your profile with our much bother.

Doc is correct in his statement about building a house around your home. Here are some thoughts.

My daughter and I are working with an architect to design her house.  The house will be heated by the sun with no extra heat input except extra warmth from appliances.  Her walls will be somewhat over R-60, thick.  

Although I have helped build some log cabins, her home will not be one.

The reason for telling you this is because she will have a double wall to  achieve that insulation rating.  Just like you are proposing to do to your house.  She will have one structural wall and an extra outside wall for the rain shield. You will also, however, need to provide another rain barrier on the outside of your new outer wall.

With any house, there needs to be vapor barrier someplace within the wall cavity.  It should be within the warmer portion of the wall (ceiling).  Most of the insulation wants to be on the cooler side of the vapor barrier so that barrier is kept warm enough to prevent condensation from accumulating and running down and rotting the wall. (remember the cool wet drinking glass in the summer as it sits on your table on those hot humid days?)

With your log wall missing some chinking, it will not prevent warm moist air from passing thru so you will need a vapor barrier someplace.  Sorry that I do not know if you live in a hot area with air conditioning most of the year, or cold like here.

There are many folks who are stripping off the siding from their home to install many inches of foam board on the outside of their walls and then adding the rain shield (siding) back. Yes you may also have to add new studs to fasten the siding to. And don't forget to understand how the windows will fit into this project.

If you do insulate on the outside of your walls, you will retain the log look in your rooms and reduce you heating costs.  I have no doubt.

The nice part of doing this your self is that you can do one wall each year to spread the cost out.

I say, , , ,       Go for it!                    Good luck and enjoy your home.

[Ljohnsaw]

After sheeting the new outside wall, you could "plank it" with slabs cut off of big logs.  That would return the log cabin look to the outside.

[Stephen1]

I do not see why you would give up the "log home".
 I would look at caulking the windows and for sure redo the log chinking outside and inside to reduce draft. Sometimes the checking in the log will run into the corners and then transfer into the house, so I would add chinking to the checks. I would add more insulation in the attic, better windows if they are old. 
I see the vapour barrier would have to go on the inside of the house, so you would be residing the house inside and outside. If you put the vapour barrier on the outside of the logs then your insulation and then your siding, would you not trap moisture in the logs?

[WillyJohan]

Yeah, realizing I should have been a little more descriptive. We actually live in the mountains of British Columbia in Canada (think north of northern Idaho), our winter has been very mild this year (though the week spell of below 0F was on the colder side for us too). Based on a more typical year, I think we'd be looking at 6+ cords a year, not totally crazy but not nothing either.

our roof overhang is bizarrely small (~18") but since we have to replace the 40 year old shakes on the roof this summer we're going to extend it as much as possible, though with the 14:12 pitch this will not be much, we think we can squeeze a couple of feet out of it before it starts blocking the windows. the roof structure is 24" oc 2X14s so i was hoping i could just line the wall furring up with the rafters and tie the siding into the soffets in some way.

not sure about siding, we've got some land up the road that we need to do some clearing on, so perhaps one of the locals with a mill could help me out in exchange for some wood or cash. alternatively there is a local commercial mill that sells their off cuts away for firewood (in line with Ijohnsaw's suggestion). either way, the total wall area is about 1200 ft2 so whatever direction we go it wont be too crazy. I kind of figure it will almost pay off through not having to reseal the logs every few years.

thanks for the info Sod Saw. were definitely in a warm side vapour barrier kind of climate, i guess i was mostly wondering if no vapor barrier would be an option, just embracing the fact that condensation will occur but ensuring that there are plenty of ways for it to dry out.

Stephan1, your last point is my primary concern. im definitely not going to refinish the inside so the vapour barrier would have to be between the logs and the insulation. as to giving up on the "log home" once you come through the front door there is no mistaking it, its really the interior where the house shines, honestly the outside is mostly roof.

[Stephen1]

Stephan1, your last point is my primary concern. im definitely not going to refinish the inside so the vapour barrier would have to be between the logs and the insulation. as to giving up on the "log home" once you come through the front door there is no mistaking it, its really the interior where the house shines, honestly the outside is mostly roof.

Between the logs and the insulation is where I am seeing troubles. I see mold forming, where the moisture from the interior condenses on the vapour barrier. 
I just touched up my chinking for the 1st time in 10 years, maybe a different chinking is needed.
I would be looking at a different heat source, checkout a Masonry heater, a radiant heat source that will reduce your firewood by over 60% It can be built where your wood stove is now and use the same chimney
Doc, big logs actually form a thermal mass, takes a long time for the heat or cold to move through them. 

[Don P]

But, if the thermal mass is inside the thermos it will perform much better.
Omit the plastic vapor retarder, the logs are a "hygric buffer" if they are well air sealed. If exterior insulation is good enough the interior surface is too warm for condensation to form and you will dry to the inside, foam probably 4" or so thick, by climate. From the foam out dries out, from the foam in dries in. Sealing/flashing the details on the exterior is tough, windows, doors, porches and entries. Windows will become even more recessed in that increased wall thickness. How to bear and support that hanging weight of foam and siding. That's just a few thoughts off the cuff.

[Sod saw]

 If foam is used as the outside insulation product it may be able to be sealed well enough to act as a vapor barrier.  If another insulation product is used, then a vapor barrier should be placed between the log and the new layer of insulation.  That location placement of vapor barrier will allow the logs themselves to dry to the inside and not have water condense into the wood logs as they stay warm.  That vapor barrier will prevent humidity from condensing onto/into the outside insulation and rain shield/siding.  (in the winter)

Now that we have talked about insulation.  How about your air infiltration?  How tight is the rest of the house?  There are folks with equipment that can measure how much air can blow in to a building and blow right back out another crack(s) taking your expensive heat with it.  Moving air will cost you more in fuel than lack of insulation.  In your case, you are concerned about the cracks between the logs, and that is a great place to start.  But, don't forget about the other "cracks" such as floor foundation, ceiling-roof, outlet & lights, and window - door openings.  If you can have some one measure the air flow, they can tell you where to place your money to get the biggest bang first off.

As for supporting that new outside "wall" and insulation weight.  I have proposed to our architect that it be supported by the roof trusses, hung.  But those trusses are able to be designed for that function.  In your case you must ask if your existing roof would hold the added weight.

[Teuchtar]

Willy, your concerns regarding condensation within walls are relevant.
We have a log home in southern Quebec. Four years ago we significantly renovated the building, adding a second floor and timberframe extension. 
After considering many alternatives, we chose to add four inches of insulation on the exterior of the original log walls. We used foam panels with an embedded furring strip. The panels are secured to the log walls using 6" screws and a 'foam washer'. Foam panels have a built-in shiplap rabbet edge and get taped with Tyvek tape. The integral furring runs horizontal. That is covered with Tyvek, then vertical furring, and finally siding. The final exterior wall looks like the original house. 
That wall insulation added a good six inches to the thickness of the wall, and pushed the exterior surface out past the foundation. You need to think about how to seal the bottom edge of the insulation, but still allow for dry air to circulate up the back of your siding. 
We find the air infiltration now is a fraction of previous and the building is economical to heat. We use mainly wood for heating, so the house tends to draw in outside air for combustion, probably reducing chances of mold in the wall.
Ive been worried about condensation forming inside the wall, but I have never found evidence of it five years after the renovation. I suppose time will tell.
I dont really like that diagram on page 9. It has so many thermal bridges to support the wood furring that  you are losing much of the insulation benefit. Also you would have much air circulation in those bridging pieces, transporting air and moisture back and forth. 
I find the arguments about thermal mass benefits of log walls essentially hogwash. The cost to heat a building is essentially about insulation, air infiltration, and moisture. Check out this (and similar) experts on youtube: 
[color=var(--ytd-video-primary-info-renderer-title-color, var(--yt-spec-text-primary))]'Building Science Insights: To Vent or Not to Vent' by Joseph Lstiburek on Youtube[/color]

[WillyJohan]

Ok, i think I've got my marching orders.

1) Spend next summer cutting up trees, lots of trees
2) replace my roof (and do a good job on the insulation + air sealing) next summer,
3) do a blower test next winter, taking some thermal imagery at the same time
4) cut some more trees down
5) the summer addressing any issues ID'd in (3)
6) see how the next winter is, perhaps do anther blower door test
7) summer 2023, see if i still feel like building a house around my house
eight) if i do, ill go with rigid foam board attached to the exterior in line with what Techtar did in Quebec


Thanks all for the input, i appreciate it.

[kantuckid]

KY is sure not BC, Canada but since we moved into my self built log home the only time we've been cold was when the fire went out for the 20 yrs we used wood only for heat. Some of those days were below zero winters, 23 degrees below is the lowest I recall but many it gets near zero here or a bit below. Air infiltration is my notion of what matters in a log home for comfort. We now use geo-thermal and while our heap lacks the radiant "feel" of wood heat, it's comfy in here.
I had an adult student years ago who was also a contractor. He built a kit log house for a client in Mt Sterling, KY not too far from me now and in the same town as the school we were in then. It was what I'll call a weird kit log home. It was PT logs, green type of salt treatment. It required building interior walls that blocked the occupants from contact with the PT wood. I've not driven by there in years but I doubt it will rot down anytime soon? :D  
My overhangs are 2' all around but much more is often seen out west-maybe 4' or so?

[doc henderson]

our home has passive solar, and the eves are designed to block direct sunlight in the summer, and let it in through the window in the winter.  might consider that with your overhang/window considerations.  your walls may be so thick, that sun cannot get in the windows anyway.  good luck, good discussion.

[WillyJohan]

regarding overhangs, seriously though, what kind of nonsense is this:

 

[Stephen1]

Overhangs are put there to protect the logs. They cost extra in the build. Most new homes are down to 6-8". I got a little carried away on my log cabin, but very little UV and no rain touchs the logs. We were a lot warmer this winter as I redid all my chinking on the logs, I even chinked some of the checking, and redid the cauiking around doors and windows.  It made big difference on drafts, which in turn keeps you warmer. This summer I will replace my last 2 homemade windows.

[kantuckid]

As mentioned already here- the southern exposure is the larger challenge to protect log walls. UV damage goes after mine bigtime and I've done several doses of finish between overall re-dos. The squirrels also like the same area. the climb up and sit on log ends and chew away at the rounded log end edges. Some have paid with their lives in fact. 

[Don P]

A porch there might help with the looks and would certainly help with weathering. 

Go carefully repeatedly recoating a log wall with layers of finish. On one of ours the homeowner repeatedly recoated the exposed southern side (with too small overhangs). The thick log siding was pretty heavily checked. The checks allowed water in, the repeated finish coats slowed drying and the logs rotted. He would have been better off with no finish.

[kantuckid]

The old part of my home has 20' of porch and 12' of front extension with the area below the picture window (on my right shoulder) and the logs below it the hardest hit.
 Kind of preaching to the choir on log finishes after this long in this building.  :D 

[bannerd]

Our neighbor lives in a log home and we had -20F for a few days this year.  Much of his heat loss happens through the roof which causes an updraft of cold air from the basement.

Instead of insulating he ended up with a thermal mass heater(soap stone)... went from 16 face cords down to 8.  Money well spent, money well saved.  

[Lyndaker]

I would definitely check for air infiltration and check into the roof insulation. We lived in a scribe built log home where we regularly hit -40 and colder and had weeks of -30 and our log home was easy to heat. In fact we used a lot less wood then our neighbours stick frame homes. Another huge source of cold is poor quality windows. Around windows and doors and the log notches and long grooves I had everything sealed. The biggest difference for us was the ceiling insulation. When we first built the house we only had 8" batts for part of the winter until I could get an insulation blower. I blew an additional 12" in the attic. As I was blowing in the insulation you could feel the temperature in each room go up as it was insulated above. After blowing in 12" of insulation over the batts we could heat with only 4-5 cords of wood a year for our 2000 sq ft house. Even at -40 we could easily keep the home above 70F. 
I don't know if you have vaulted ceilings or not but they are also a big source of heat loss.