by Kenton Shepard
Certified Master Inspector
InterNACHI member
Log home types fall into two categories, Handcrafted and Manufactured.
HANDCRAFTED LOG HOMES
There are two basic types of Handcrafted homes…
a. Scribe-fit log homes are built using naturally-shaped wall logs which are each
marked and cut to fit snugly over the log in the course below. A gasket material
is installed between each course to help prevent air, moisture and insect infiltration.
b. Chinked log homes are also built using naturally-shaped wall logs, but logs
are cut to fie over each other only at the corners. Between corners, spaces between
logs are sealed with grout mix (older homes) or with a caulk-like material. Chinking
materials have improved greatly as materials technology has progressed.
Extreme Settling in Handcrafted Log Homes
What is settling?
Settling in log homes is the term used to describe the loss of log wall height
over time. During the first two years when the majority of wall log settling takes
place, a wall may lose ¾ inch per foot of wall height. This means that an 8 foot
tall wall may lose up to 6 inches in height before it has finished settling.
Causes of Settling
The principal causes of settling are…
1. Shrinkage of log diameter as the logs dry to a stable condition. This condition
is known as Equilibrium Moisture Content (EMC). EMC is reached when the log moisture
content is equal to the average relative humidity of the home site.
2. Wood compression: Over time, the weight of the structure will compress wood
fibers, causing the wall logs to settle. Compression causes less settling than
shrinkage.
Green Logs
Logs with moisture content greater than 19% are called "green" logs. Walls built
of green logs can settle up to ¾ inch per foot. They will not reach EMC through
air-drying on-site and this process may take up to 5 years as part of a heated
home. There are advantages to building with green logs related to controlling
checking, ease of cutting and controlling log fit over time.
Dry Logs
Logs with moisture content equal to or less than 19% are termed "dry logs". Because
a log with 19% moisture is a "dry" log and one with 20 % moisture is a "green"
one, these two logs will obviously differ very little in the amount of shrinkage
that has taken place as they approach EMC.
Kiln-dried logs are available but are expensive. Many modern, preassembled handmade
homes are built from standing dead trees.
Settling Rates
Both green and dry logs will continue to shrink (and settle) until they have
reached EMC.
Free water is moisture trapped between wood cells within logs. No shrinkage occurs
while logs are losing free water. Logs may lose half their weight as free water
evaporates with no shrinkage taking place.
Bound water is moisture trapped within wood cells. It is not until bound water
begins to evaporate that shrinkage begins to take place and logs can reach EMC.
The time required to reach EMC varies with wood species, log diameter, initial
moisture content, interior home temperature and local climatic conditions.
Checking
As logs shrink, they develop surface cracks called checking. Logs usually develop
a single dominant crack, the location of which can be controlled by kerfing the
log (making a saw cut down the length of the log).
There will be secondary checking which, when it is located on the upper surface
of the logs, will catch and hold moisture. To avoid establishing pockets of wood
decay and damage from the freeze/thaw cycle in these upper surface checks, they
should be filled with an appropriate material.
Special Construction Methods
The large amounts of settling possible in handcrafted homes means that special
building methods are required to prevent damage to home components such as doors,
windows, trim, stairways, conventionally-framed partition walls and home systems
with rigid components like plumbing pipes and electrical conduit.
In many situations, confirmation that these methods have been used will require
invasive measures that lie beyond the scope of the General Home Inspection. This
should be clearly stated in Home Inspection contracts.
Log Building Standards
These standards have been developed to set minimum guidelines for log home construction.
They are worth taking the time to read.
More information on Handcrafted log homes (including the Standards mentioned
above) can be found at the web site for the International Log Builders Association
(ILBA)
http://www.logassociation.org/
MANUFACTURED LOG HOMES
Manufactured log homes are built with logs that have been milled to a uniform
diameter. Logs usually have a profile milled into the top and bottom that allows
each log to interlock with the log in the courses above and below. Interlocking
profiles also add strength to the wall and help prevent air, moisture and insect
infiltration.
Milled logs may be cut square or milled to a "D" shape to provide an interior
flat surface to which drywall or a furring wall may be more easily attached.
More information on manufactured log homes can be found at the web site for the
Log Homes Council http://www.loghomes.org/
LOG VENEERED HOMES
Homes are sometimes framed conventionally then sheathed on the exterior with
veneer milled to a profile that provides a log home appearance.
PREVENTING MOISTURE PROBLEMS
Exterior Finishes
Log homes must have a finish applied that will allow moisture vapor to pass through
the finish while water in liquid form is kept out.
Using a waterproof finish will trap moisture inside the logs and can cause logs
to decay from the inside, where decay can remain hidden until the logs have lost
too much strength to be saved. Whole homes have been lost in this manner.
Sill Log Height
Sill logs are the lowest course of logs. It is recommended they be a minimum
of 12 inches above the ground to minimize splashing and snow drift contact.
Roof Overhangs
The ILBA Log Building Standards recommends a ration of 8:1 for roof overhang
lengths. Longer overhangs help protect wall logs from weather.
Gaskets
The presence of gaskets installed between log courses to help prevent moisture
and air infiltration can sometimes be verified by examining exterior corners.
Flashing at Openings and Terminations
Flashings around door, window and wall terminations should be examined closely.
INSPECTION of LOG HOMES
Log Home Standards of Practice
Although Standards of Practice are now being written and reviewed by a committee
appointed by the International Association of Certified Home Inspectors, no Standards
of Practice for inspecting log homes have been established as of 8/22/06. The
rough draft of these standards my be available online but are not in effect or
binding upon any inspectors.
Limitations of Log Home Inspections
Log homes have been and continue to be constructed using a large variety of methods.
The nature of some of these methods makes it difficult or impossible to confirm
that extreme-settlement construction techniques have been used without using invasive
measures.
In order to protect themselves and their clients, Home Inspectors inspecting
log homes should be familiar with the various types of log homes and the methods
and instruments required to inspect them properly. The only course available
is one offered through the International Association of Certified Home Inspectors.
Understanding the limitations on inspections posed by various log home types
is even more important. The limitations should be clearly explained to clients
before the start of the inspection and be stated clearly in the contract signed
by the client.
Sources of information on log homes:
GENERAL INFORMATION
WOOD-DESTROYING FUNGI (WOOD DECAY)
-Information for this article comes primarily from the sources listed above.
