Log Home Basics

by Kenton Shepard
Certified Master Inspector
InterNACHI member
www.peaktoprairie.com
peaktoprairie@msn.com
 

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.