The words "settling" and "shrinking"
invoke fear in the hearts of many future log home buyers.
This shouldn't be the case, however, because the business
and practice of building log homes has been around long
enough such that the "problem" is well understood
and is really not a problem any more. However, it's
a topic that needs some understanding and consideration.
The Facts
Let's start with some facts. Logs are "wet"
or "green" (contain a lot of water) when cut
from the forest (exception: standing-dead trees used
primarily in handcrafted homes). After being cut, logs
will slowly start to lose water to try to match the
ambient air moisture content. As logs dry, they shrink,
which can cause checking, warping, and twisting. The
degree to which these effects occur depends on the wood
specie and drying environment. The purpose of managed
drying is to pre-shrink logs and make them more stable
before they are used in construction. When logs are
stacked in log walls, even after drying, they can settle.
Settling can be significant enough to require special
construction techniques to compensate — or not.
About Settling
Settling is made up of two factors – shrinkage
and compression. Both contribute to a possible reduction
in height of stacked log walls. In a 10-course log wall,
1/8 inch shrinkage in each log means a total 1.25 inches
for the wall. Significant settling can cause problems
that range from serious (separation of walls from roof),
to relatively minor (windows and doors that stick).
Shrinkage is a reduction in log dimensions. Some wood
types shrink more than others. Some wood types shrink
in different ways than other types. Individual logs
of the same wood type can have different shrinkage characteristics.
All woods shrink less when dry.
Compression is caused by the weight of logs stacked
on top of each other. Fibers in the wood are forced
closer together, which reduces the size of each log
in a vertical direction. Compression between logs is
good in that it helps create tight joints. Proper drying
minimizes or eliminates the effects of compression.
Log home companies fall into one of two categories
regarding how they handle the possibility of settling.
Some companies simply ignore settling or declare it
to be insignificant, which may be perfectly justified
given the wood species they use, their drying method,
construction techniques, and their experience. These
companies make no special provisions for settling.
Other companies believe that settling deserves some
attention, even if the possibility is slight. These
companies may use a combination of springs on bolts,
slip-mounted cabinets and trim, floating interior walls,
jack screws, and settling space above doors and windows.
Which philosophy is correct? To be honest, it's not
clear. To a large extent, we have to trust our chosen
log home company to know their business and understand
which philosophy works for them. However, it is our
opinion that adding slip joints, floating walls, and
settling spaces above doors and windows is very inexpensive
insurance against the possibilty of problems in the
future.
