Logs are made of cells bound together to make the fibers of a tree that run longitudinal (the length of the tree). These fibers pull nutrients up from the base to feed the tree. The water in the cells is called “Bound Cell Water” and is one major cause of log homes settling and should be a very high concern when selecting a log home manufacturer.
Trees die in the forest from disease, insect infestation, forest fires and old age. If the tree dies of forest fires or old age they become prone to disease and insects. If the bark doesn’t come off the trees after they die the bark becomes a moisture barrier and in 30 days decay will begin on the fibers. It is a natural process that nature uses to clean up waste.
As a log loses the bound cell water it will shrink only in diameter. The fibers are like straws and as the water dissipates these fibers collapse basically imploding towards the center of the tree. It is like an apple you sit on the counter and it shrivels up.
There are 3 different kinds of logs used in the log home industry.
1) Live green trees
2) Dry dead standing
3) Cants (a bi-product used in the industry)
*note see Kinds of Logs section*
Depending on the kind of logs are used, your logs will shrink at different rates. Look for a log home manufacturer that will provide you with a constant moisture content and be willing to write down that you will never have to chink your home. Dry dead standing or what some refer to as air dried will have a variable moisture content on the interior of the log depending on how long the dead tree stood in the forest before being harvested. *note see Moisture content section*
Most all log home manufacturers are mixing log species (white pine, yellow pine, fir and spruce) up to 10% in their walls giving you a butcher block look. Each species dries at a different rate and will cause structural problems as the logs shrink. You will never be able to stain your home to a uniform color unless you paint it with a solid color.
To know if a manufacturers product will shrink ask if they use settling or screw jacks on their vertical poles *note see Settling/Screw jack section*
Screw-jack below in photo creating gap between header and vertical pole to allow for settling.
Some log home manufacturers that harvest green trees have a process where their kilns can get to the center of a log and dry to a constant moisture from one end of a log to the other and all the way through. These logs will have the least amount of settling in the log home industry and I would suggest you look for one of these log home manufacturers to eliminate excessive maintenance costs. Do your home work and ask lots of questions and get information in writing.
Notice the “slips” over this window. On handcrafted log homes the builder calculate how much the home should shrink and allow for this over the doors and windows. This area is packed with insulation to slow heat loss and hopefully when the wall settles down it will not crush the doors and windows.
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We are builing our white pine log house ourselves. We cut and milled our white pine logs to 8″ square two years ago. They are situated in Otter Lake, Quebec and they are stacked and open air drying in an open field. They are covered loosly with a tarp roof. I expected them to shrink a half inch (8 x 1/16 = 8/16 = 1/2″). My husband measured a few of them yesterday, March 19, and they are still 8″. They seem to be defying all the rules. We plan to start to build next year, April 2012. I don’t know if I should write my plans using 8″ or 7 1/2″. At 8″, it means one less row of logs. Please help.