Sunday, April 02, 2006

Log Home Questions Answered(?)

Appalachian Gun Trash has some questions about the construction of our log home among the comments to my last post. Allow me to try and answer.

Styrofoam forms... I think I first saw that one on This Old House a few years back. It was pretty interesting and amazing to me that stryofoam could take all that concrete. I've seen poorly braced plywood forms bow under all that pressure so it was amazing to see them pouring all that readi-mix into a form made out of coffee cups. :-)
You know, when you think of it as “coffee cups” it is amazing—and scary. The form is actually a high-density styrafoam similar to the packaging you’d see used for computers and TVs. It’s strong stuff! Two two-inch layers of this are held apart/together by separators to create an 8” channel between them. The contractor will stack these forms and join them using an adhesive . (It’s like playing with life-size Legos.)

These forms will, when filled with concrete create a 12” thick wall (8” concrete with 2” of form on either side. Around the garage, or any where there’s no basement or crawl space they will rise 40” above the footers. Thirty-six of those inches will eventually be buried below grade. In the basement area, they will rise far enough to yield a 9’ tall ceiling. The forms stay in place to produce an insulated foundation that will help conserve energy.

What method do they use to fasten the logs to each other? Galvanized spikes (60d or so) or threaded fasteners?
We have chosen a 8” x 8” milled log with a D-profile (inside is flat the outside is rounded). In the milling process Beaver Mountain Log and Cedar Homes places a double tongue and groove on the tops and bottoms of the log. They also pre-drill each log so it can be attached to the log below using a 3/8” lag bolt. Since our logs are 8”, I believe the lag bolts will be 12” long.
Rather than chinking between logs, the tongue-and-groove system, combined with foam tape atop each of the tongues and a line of caulking along the outer tongue, serves as an air barrier.

Also, do they have some sore of method to compensate for any drying/shrinkage in the logs? I was always curious about that one.
Beaver Mountain kiln dries their logs before the milling process begins to about 18-20% moisture level. During this process enough moisture is driven out to cause some checking in the logs. (Checks are the cracks and splits that occur due to differential shrinking of the cells in the log.) At every step of the milling process they grade the logs to remove those which have overly large checks. You can’t get rid of all of the checks but they try to keep them to less than 1/4” in width. (They also remove those pieces that have too many knots or that peel when run through the shapers. If they don’t like the way it looks—out it goes.)
Once on the building site and stacked into the walls, there is very little, if any shrinkage. You may get the same amount “breathing” you would get in a standard stick-built home. (I call it “breathing” but it is the expansion and contraction that causes the creaking you hear in a home over the course of a day or a year as the temperature and humidity change.) Even so, you do leave a little 1” gap at the top of each door or window that will be insulated with fiberglass so if there is any settling the doors don’t jam and the windows don’t crack. That’s really no different than a stick-built home.

Also, do you plan to treat your logs with anything after the house is up?
The exterior of the logs will be treated with a wood preservative once construction is completed. They will then have to be retreated every 3-5 years depending upon environmental conditions. We shouldn’t have a problem with bright sunlight (the house site is on the north side of the hill) so we will be looking at the longer time frame. Inside there will be a sizing used to seal the wood grain. There are several options of staining and finishing available to us but we haven’t settled on any one yet.

I hope I’ve been able to answer your questions AGT. (BTW: When are y’all getting back to work on your project?)


Gun Trash said...

Thank you for the answers. It all sounds darned interesting. I like the concept of T&G logs, that along with 3/8 lags should make for a pretty darned solid construction. Sounds as though they've got it fairly well engineered and designed.

Just curious, what is the R rating of 8" diam logs. I imagine it would provide at least R-12 or thereabouts?

Our project... I was just out there today doing a mental build schedule. So hopefully, this week we can get back into it.

Anonymous said...

Interesting Read! -- Good info.

R rating of logs depends upon the species of log.

Cedar, I stick my neck out and assume that Beaver Mountain Log Homes being in NY state use Eastern Red Cedar. Although Eastern Red Cedar (Juniperus virginiana) has rather poor strength - it has excellent decay resistance and is comonly used for log walls. It also has very little radial shrinkage. R value or Eastern Red Cedar is approximately 1.03 per inch -- so if your walls are 8" that would be an approximate R value of 8.24.

Cedar is of medium R value. Most of your R value concern will be in the roof since heat rises.

If this is not red cedar and they are using Eastern White Pine - (common material for the area) then the R value will be quite a bit higher being 1.32 per inch giving you a total of 10.56 in R value for an 8" wall.

Love to see the progress of you home! Very exciting.

joated said...

I believe Beaver Mtn. gets its cedar logs from out west.

Our home is using Eastern White Pine grown in NY and PA.