Log cabin SIPs? (Conventional log walls insulated with foam in the middle)

[Badfish740]

A while back there was a debate going on about ICFs (Insulated Concrete Forms) and other types of high efficiency insulation/construction methods. SIPs are the pre-fabbed panels made from OSB on either side and high r-value foam insulation in the middle which create a strong, airtight, and highly insulated wall. Most are rated around R-30/R-40 depending on thickness and type of foam. Anyway, SIPs are nice, but my wife and I have always wanted to build a log cabin. Log cabin walls only rate about R-8 because solid wood is about R-1 per inch. Some folks do log cabins this way by constructing outer log walls, applying foam insulation to the inside, and covering it with sheetrock, but we want the log look inside just as much as the outside, so I started thinking.

What if you could construct inner and outer log walls (both 8" thick, which would create an R-16 wall right off the bat) and fill the center void (also 8") with expanding spray foam like the type that is typically used in stick framing? Most closed cell spray foams are rated around R-6 per inch. The other advantage of expanding spray foams are that they fill gaps that normally wouldn't be able to be filled, so zero air infiltration/leakage can be achieved. The resulting wall would be just over R-60! The only other construction methods I've seen with that type of rating are straw bale/stucco homes. Conventional OSB/foam SIPs could be used for the roof. I just wonder at that point, in our climate (Northwestern New Jersey, where -10 is about as cold as it ever gets, and even that is rare), what kind of heating system would that require? Would even a small wood boiler cook us out of the house? The air conditioning bill would be pretty nice I would imagine

Obviously construction costs would be an issue, but our length of return on investment would be high-whenever we build our home we intend to be there til the end, come hell or high water. Just curious to see what others think of the idea, or if anyone has heard of anything similar?

 

[colebrookman]

You may also want to consider using conventional SIPS with half logs both on the inside and outside. The products are easily available, look good and give the option of using dry wall if needed on the inside. Plus it keeps things simple and less costly. Just another idea. Be safe.
Ed

 

[Badfish740]

You may also want to consider using conventional SIPS with half logs both on the inside and outside. The products are easily available, look good and give the option of using dry wall if needed on the inside. Plus it keeps things simple and less costly. Just another idea. Be safe.
Ed

I thought about that option but you just don't get the real log look from the "log siding." Especially on the corners-growing up in a log home I always thought that the interlocked corners on the inside and outside of the house were one of it's most distinctive features. That and we're even thinking of doing interior log walls since we don't really want drywall at all. There are companies that simply sell logs in any shape and length you want that you can have shipped to your site and assembled any way you like, which appeals to me since we wouldn't then be locked into any kind of kit design. I haven't done the math on it but the logs I would want (8" x 8" D-shaped for the outer wall and 8" x 8" square for the inner wall) run about $4.50 per linear foot, not counting delivery. Obviously the cost of materials for the inner and outer walls would double, plus the cost of the foam insulation. I'm curious about that as well because I am seeing lots of DIY kits being peddled over the internet and I wonder about the quality vs. a pro installation. I'm a very experienced DIY'er, but I wonder about the quality of material and equipment that's available to the general public. Anyway, the prospect of such a high r-value wall along with zero air infiltration is still very enticing, but it will be a matter of crunching some numbers with regard to how much I would save in HVAC costs over the years.

The next thing to ponder in this whole equation is supporting the walls. In parents' home as in most conventional log construction, the weight of the outer walls bears directly on the foundation walls, so its a straight shot down to the footings, which makes perfect sense since you're dealing with the weight of the roof being transferred through the walls, along with the considerable weight of the walls themselves. In the case of the idea I've come up with now you have an inner wall which would bear down on the unsupported span of the floor joists. This I suppose is a question for an engineer, but one worth exploring here in case anyone has ideas. I'm guessing that with a stout set of engineered wood I-beams this could be managed. The average 8' high log wall weighs 180lbs per linear foot. I have no idea how much the average stick built wall weighs (I suppose I could estimate with a scale, 2x4s, drywall, insulation, etc...), but nevertheless if the front wall of my house is 60' long that adds up to a nearly 11,000lb load on the unsupported span of the floor joist. Just thinking out loud here...

 

[colebrookman]

As for the corners , there are companies that sell whole log corners so they look like the real thing. I know it's hard to change when you have your heart set and know what you want but there are many ways to achieve the perfect home. Best of luck and please keep us posted on your progress. be safe.
Ed

 

[SE Iowa]

I live in an all icf home. My brother lives in an all log home. We helped each other build. As for my brothers place, if he had to do it all over again he would stick build the house and add log siding to the outside and car-siding to the inside walls. As said before they make log siding with corners to look like real logs all around. In addition, most logs are squared off for the inside wall so that it looks like car-siding when built. You could have the efficiency of the SIP's and the look of logs. BTW, my brothers roof is a SIP-style roof. Just my 2 cents.

 

[Dune]

Sounds expensive but worth it if you can afford it.

 

[Hunderliggur]

I have a 6" cypress D-Log house with an ICF basement. The logs are very nice but they are HEAVY and TIME CONSUMING to erect. Even with that, we love how the house feels. I looked at one double wall pine log design which was OK, but the cypress provides natural decay and pest resistance. I would not put a log wall above anything but a foundation wall. The weight is huge and your wood system will deform over time. The Department of Energy has a efficiency calculator call ResCheck which will give you the energy performance for a log home. Not including passive orientation, my 6" cypress system works out better than the code (R-19) in my area. My house is long on the E-W axis with plenty of southern glazing (but not too much) and large overhangs (necessary for shading and even more importan to protect the logs). We have log siding on the garage over typical frame. It looks fine with the rest of the house, it is hard to tell the differece on he outside except for he corners. You may want to go with 8" logs, spray foam the outside of the floor trusses, insulate te heck out of the attic, and take what you would spend on the second log wall and put in some active solar (or a wood gassifier).

 

[Badfish740]

I have a 6" cypress D-Log house with an ICF basement. The logs are very nice but they are HEAVY and TIME CONSUMING to erect. Even with that, we love how the house feels. I looked at one double wall pine log design which was OK, but the cypress provides natural decay and pest resistance. I would not put a log wall above anything but a foundation wall. The weight is huge and your wood system will deform over time. The Department of Energy has a efficiency calculator call ResCheck which will give you the energy performance for a log home. Not including passive orientation, my 6" cypress system works out better than the code (R-19) in my area. My house is long on the E-W axis with plenty of southern glazing (but not too much) and large overhangs (necessary for shading and even more importan to protect the logs). We have log siding on the garage over typical frame. It looks fine with the rest of the house, it is hard to tell the differece on he outside except for he corners. You may want to go with 8" logs, spray foam the outside of the floor trusses, insulate te heck out of the attic, and take what you would spend on the second log wall and put in some active solar (or a wood gassifier).

Great advice-thanks!

 

[Reggie Dunlap]

You're going to spend a fortune on the construction of your shell. The walls would be 20" thick, window and exterior door jambs would take a lot of labor and look pretty strange. Doors would need to swing out or they would hit the jamb.

A less expensive option would be 2x6 walls with foam insulation and log siding inside and out. Or V-groove pine, spruce, cedar on the inside.

Or build a traditional log cabin with 8" D-shaped logs and install 2" foil-faced Celotex over the inside of the logs. Then strapping with pine, cedar, spruce over the insulation. The walls would be 11" thick and the 2" insulation would give you a place to install the wiring.

Hope this helps

 

[Seasoned Oak]

When you approach R60 in the walls most of your heat will just go through the doors and windows. There is the law of decreasing returns. You will lose a ton of floor space inside a house with a 20" wall width. my ideal house would be SIPS in the middle log siding on the exterior and whatever is your fancy inside.

 

[Hunderliggur]

One log home manufacturer already does smething like this:
"One of the modifications the owners of this cabin requested was the addition of Katahdin's Energy Envelope System. The system creates continuous insulation that significantly improves energy efficiency, while maintaining whole-log construction. "We've had increased demand for an enhanced insulation system for our already efficient cedar log homes," explains David Gordon, president of Katahdin.

The company's energy envelope is constructed from the log wall exterior toward the interior. A 1 1/2-inch layer of foil-faced rigid insulation is applied to the interior of the Northern white cedar log wall. Then, an insulating 3/4-inch layer of air space is created by applying thin strapping strips to the rigid insulation. Finally, the interior is finished with tongue-and-groove cedar, shaped to a round or flat profile. An added benefit of this system is that is allows for easy electrical wiring. With the Energy Envelope System, David Gordon says, "Katahdin home buyers will find themselves prepared to meet or exceed most energy challenges thrown their way."

 

[vvvv]

A while back there was a debate going on about ICFs (Insulated Concrete Forms) and other types of high efficiency insulation/construction methods. SIPs are the pre-fabbed panels made from OSB on either side and high r-value foam insulation in the middle which create a strong, airtight, and highly insulated wall. Most are rated around R-30/R-40 depending on thickness and type of foam. Anyway, SIPs are nice, but my wife and I have always wanted to build a log cabin. Log cabin walls only rate about R-8 because solid wood is about R-1 per inch. Some folks do log cabins this way by constructing outer log walls, applying foam insulation to the inside, and covering it with sheetrock, but we want the log look inside just as much as the outside, so I started thinking.

What if you could construct inner and outer log walls (both 8" thick, which would create an R-16 wall right off the bat) and fill the center void (also 8") with expanding spray foam like the type that is typically used in stick framing? Most closed cell spray foams are rated around R-6 per inch. The other advantage of expanding spray foams are that they fill gaps that normally wouldn't be able to be filled, so zero air infiltration/leakage can be achieved. The resulting wall would be just over R-60! The only other construction methods I've seen with that type of rating are straw bale/stucco homes. Conventional OSB/foam SIPs could be used for the roof. I just wonder at that point, in our climate (Northwestern New Jersey, where -10 is about as cold as it ever gets, and even that is rare), what kind of heating system would that require? Would even a small wood boiler cook us out of the house? The air conditioning bill would be pretty nice I would imagine

Obviously construction costs would be an issue, but our length of return on investment would be high-whenever we build our home we intend to be there til the end, come hell or high water. Just curious to see what others think of the idea, or if anyone has heard of anything similar?

The foam may not expand/contract but the wood does & I'd guess infiltration cracks would eventually develop.

 

[HowlingMad]

Not sure if it was mentioned in here, but condensation in between the two walls could create a real problem for you. I too considered something like this but stopped at that issue. Mold sucks.

 

[begreen]

I was looking into this about a decade ago. This product is made locally in WA state with cedar outer/inner logs and a foam core.
http://www.singloghomes.com/index.php

Looks like now there are many more choices:
(broken link removed to http://www.homesteadtimbers.com/laminated_full_logs.html)
(broken link removed to http://www.eaglepanelsystems.com/log-home.html)