More Q&A Spotlight
Early settlers who felled their own trees to build log homes were probably so grateful to be out of the weather they didn’t worry about air leaks or cold walls. But when your heating bills are $500 a month, it’s a different story altogether.
That’s the situation facing ADK Homeowner, as he explains in a Q&A post at Green Building Advisor.
“Built the dream log home and now face the heating nightmare in Climate Zone 7,” ADK writes. “A masonry heater reduces the heating load of my in-floor heating system by half but without it my heating bills [average] $500 a month.”
ADK has a plan. On the inside of his log walls, he wants to install between 1/2 inch and 1 inch of rigid foam insulation, followed by log siding installed on the interior (to preserve the aesthetic he liked so much to start with).
“I am thinking the rigid foam provides a thermal break and the log siding maintains the log look,” he writes. “The insulation and log siding will not be cheap, but my heating season goes from late October through March or early April, and at least three of those months have many sub-zero days. I can afford to lose the 2 inches to 2 1/2 inches of space per room and the labor would be mine.”
Will it work? Or is this plan just plain crazy? That’s the subject of this Q&A Spotlight.
You need more foam
“The easiest thing to do is to sell your home and buy a home with tight walls,” counsels GBA senior editor Martin Holladay. “It’s very hard to fix log homes.”
Holladay’s suggestion may be tongue-in-cheek, but he’s certain that ADK’s proposed foam layer isn’t nearly thick enough. He should really be looking for a way to add…
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10 Comments
Insulating log homes.
Interesting to hear from someone about their log problems. Some 40 plus years ago I built a two story log home in the middle of a woodlot, using vertically placed 4" milled double T & G northern cedar. Inside the basic log structure I placed 4`x8`sheets of 1.5" foam with joins well taped then inside that built a complete 2"x4" wall (with no fastenings through the foam), with conventional batt insulation, poly vapour barrier, and drywall downstairs and wood upstairs to finish the interior. Our heat was a wood stove plus a wood furnace in the basement for cold weather use. It all worked pretty well, and seems to have lasted without problems to this day.
My next door neighbour built a conventional log home, and had excessive movement and even major structural issues. It never worked right!
My general recommend is to treat log structures generally as `structural siding`, and place something conventional inside them to do the real work of the house.
Regards, Tony.
Air leakage seems suspect, plan seems workable...
IF the logs were well sealed they should give an R-value of about R8, about typical for an R13 stud wall. Assuming an interior temp of 70degF, however, the wall temperature in the low 50s indicates an effective R-value of more like R3.5 indicating lots of infiltration: not efficient, not comfortable.....but the air won't feel stale!
On the other hand, even adding 1" of polyiso would add R6 and reduce the air leakage, thus increasing the logs to more like R8 and the whole wall to R14, a 300% improvement. Ignoring the infiltration benefits still improves R from 3.5 to 9, a 150% improvement.
Lincoln Logs Company in the Adirondacks
Lincoln Logs had a model home decades ago that leaked between the logs. They and many of the log home companies changed their building details. As to the model, it was pretty cold and drafty on windy days... they clear siliconed leaky log stacks and then added matching pine T&G so as to still look like logs.
Rescheck does a good job of telling how much of a hit logs are. I just designed a log cabin for hunting that we had to jack up all the other areas of insulation double and include R-5 triple pane windows to get the 2010 rescheck to pass at 0% passing.
For a fun second home little hunting camp with a woodstove... they make sense. As always it's a personal choice, an aesthetic.. a lifestyle... a little Daniel Boone in some of us...
Disclaimer; before biting into the green world I built way too many log homes... get this... heated by... electric baseboard heat... and a woodstove.
The salesman woman.... get yaa smiling and nodding... and loving... "the warmth" that you will be enveloped in from your logs... all the heat the hold... and give off!
LOL... pays the bills... people want what they want... like trying to walk a cat on a leash.
Personally.. love green... love PGH.... love log homes.. and all those that build period. Oh and have to add love all those that work at LL and sold for them and those that do now... the new LL owned by a local Lumberyard company now.
best of both worlds?
we hit on a potential solution for retrofitting log homes without sacrificing too much of the aesthetic...the two walls visible from the driveway, skin those on the inside (so you can still see the logs on the outside). And then the two walls away from the driveway, larsen trusses on the exterior. That way you can still see many of the logs, and you get to worry about the thermal bridging in the corners where the inside/outside insulation layers transition.
Reply to Blake
I can see the logic but it does go against one of the fundamental design tenants we were taught in architecture school that you never change exterior finishes on an outside corner, as it makes them appear paper thin with no volume.
Chinking as air sealing?
I currently Live in a log cabin and I was wondering what the thoughts were on chinking the cabin to help air seal. Currently, mine has no chinking inside or out. I have not done any thermal imaging but when I put my fingers in the places two logs meet I can feel it is significantly colder.
Thoughts?
Chinking leaks.
Chinking usually leaks air after a full year of thermal & hygric dimensional changes of the logs, but it's WAY better than un-chinked logs!
There are likely to be good/better/best methods & materials for chinking, but I have nothing specific to recommend.
To really air seal a log structure requires building a true air barrier on one or both sides of the walls.
I have been planning to build a small, milled (8 inches) logs house. I've been leaning toward coped logs, instead of T&G attachments, because I can buy coped full-length logs cut as dead standing timber (so drier) from Idaho. The house is only 840 square feet. I had first thought I would build 2X4 walls against the milled logs interior surfaces, but only in the kitchen, bathroom and the one bedroom. Thought I'd insulate with batten and then 1/2 inch foam outside, to which I'd attach drywall or decorative thin tongue and groove boards. I've assumed if leaving the milled logs exposed in the living and dining rooms turned out to be too cold (North Dakota), I could finish those areas in the same way later.
But in a prior article I just read that building an interior wall-with-tight-insulation causes its own problems with cool damp logs and future moisture risks. That caught my attention, never having heard or read of that problem before. Is there a way to mitigate this problem when finishing walls inside the log casement? I'd prefer less warmth to more moisture.
Another issue: I have been thinking of installing small gauge rebar in a groove I will cut on the top and center of each log, running its full length. I am building in a remote location and may or may not live there 12 months annually. I don't want to return after an absence to discover someone decided to enter with a chainsaw. Will the rebar running along each log create a lightning hazard? I am guessing I will have to ground each section, connecting wire to each embedded length of rebar, but don't know about this. (Bet you've never run into that question before)
Thanks, great information and advice here.
Cowboy,
First, you should know that there are no advantages whatsoever to log construction compared to frame construction, unless you live in a very remote location where the only access is via a footpath.
As you correctly note, the only reasonable way to insulate log walls is to install interior framing, at which point the question arises: "Why not build a frame house? I have to buy the 2x4s or 2x6s in either case, and logs make lousy siding." (Old log houses often have exterior moisture problems, due to wind-driven rain, unless your building has very wide roof overhangs.)
The key to a high-performance wall is air sealing. Insulation details are secondary. Make sure your walls are airtight -- not easy with log walls, but possible if you install interior framing.
If you can make your walls airtight, the moisture problems in your logs will all be due to exterior moisture (rain), not interior moisture traveling through the walls by diffusion.
Cowboy,
Practically, the problem with building interior framed walls is that they don't move while the outer log structure shrinks and settles. That means you need to stop them shy of the ceiling and build in slip-trim which can cover the gap, but also move as the gap diminishes over time.
More difficult is at windows where the framed interior and log exterior openings will over time not line up, and you will also need slip-trim around the exterior window casing.
The differential movement also means air-sealing is a challenge. These hybrid structures are really complex. If you decide to go that way, spend a lot of time working through the details in advance. They aren't things you can work out on site as you go.
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