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LOG HOME BASICS
By Kenton Shepard
First built around two thousand years ago, log homes have been built using every method imaginable.
Modern log homes have become much more sophisticated in the past thirty years due to the invention of new building methods, efforts at standardization and advances in materials technology. Log Building Standards are now available from both the International Log Builder's Association (ILBA) and the International Code Council (ICC).
Log homes are divided into two types, Handcrafted and Manufactured.
HANDCRAFTED LOG HOMES
Scribe-fit logs at window openings. The slot in the log ends will accept a spline to keep the logs aligned.
There are two basic types of Handcrafted homes…
- Scribe-fit log homes are built using naturally-shaped wall logs which are each scribed 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.
- Chinked log homes are also built using naturally-shaped wall logs...
- With one common method, wall logs are cut to fit over each other only at the corners. Between corners, spaces between logs are sealed with grout mix (historic homes) or with a modern, UV-resistant, caulk-like material. Chinking materials have improved greatly as materials technology has progressed.
- Using another often-seen method, naturally-shaped wall logs are notched to fit over each other but are also sealed with chinking to avoid air, moisture and insect infiltration.
 
It took builders a while to refine the art of scribing-fitting... ...but they finally got the hang of it!
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Scribe-fit cedar logs with lots of taper. Notice how the direction of taper alternates with each course.
WHO BUILDS LOG HOMES?
Although custom log home builders still exist who will build on a homesite with delivered logs or logs cut onsite, a much more common scenario is one in which log home builders first assemble the log home shell in the company yard.
Once the shell is assembled in the yard, it’s disassembled, the logs are marked for re-assembly and the entire log shell is loaded onto a truck and delivered to the home site. If everything is ready and the weather cooperates a 2500 square-foot home can go up in two days.
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 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…
- 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.
- 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
According to the ILBA Log Building Standards, logs with moisture content greater than 19% are considered “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.
Although it's widely thought that building with dry logs is preferable to building with green logs, there are advantages to building with green logs...
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Typically not sapstained
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Logs have little or no checking, making them easier to scribe.
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Logs can be kerfed to control checking.
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Ease of cutting, log splinter less when cut.
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Controlling log fit over time.
Some very experienced log builders have good things to say about building with green logs.
Dry Logs
Logs with moisture content equal to or less than 19% are termed “dry logs”. Although 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.Many modern, preassembled handcrafted homes are built from standing dead trees.
Kiln-dried Logs
Kiln-dried logs are available but are expensive. Kilns are buildings in which logs are placed for controlled drying. The building interior is heated to around 170 degrees F. and fans circulate the air to keep the temperature uniform. As moisture evaporates from the logs, moisture is removed by de-humidifiers.
The process must be carefully controlled so that log interiors and outer surfaces dry as closely as possible at the same rate. If the difference between inner and outer drying rates is too great, checking may be severe.
The average moisture percentage is typically checked by weighing a sectio of log beforfe and after all residual moisture has been removed. The final result varies from one kiln to another but moisture levels are typically below 19%. There are no industry standards for kiln-dried logs.
Settling Rates
Home logs in warm, dry climates will typically lose moisture more quickly than those in cold, damp climates because the evaporation rate will be higher in the former. Both green and dry logs will continue to shrink (and settle) until they have reached EMC.
Logs are made up of billions of wood cells which are like microscopic straws...
Free water is moisture trapped between wood cells within logs. No shrinkage occurs while logs are losing free water. Logs may lose as much as 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 fiber saturation point is the point at which free water is gone and a log starts to lose it's bound water. Moisture content at this point is about 28%.
The time required to reach EMC varies with wood species, log diameter, initial moisture content, interior home temperature and local climatic conditions such as the average annual humidity.
Inspectors can use a high-quality moisture meter along with their knowledge of local humidy levels to develop a rough idea of how far along with the drying/settling process the home logs are.
A chart showing average monthly and annual humidity levels for many cities nationwide is available from the National Climatic Data Center.
Example:
Average realtive humidy shown: Morning/afternoon
Jan Feb March April May June July Aug. Sept. Oct. Nov. Dec. Annual DENVER, CO 63/49 67/44 67/40 67/35 70/38 69/35 68/34 69/35 68/34 65/36 68/49 65/52 67/40
The table below shows the approximate moisture content of wood at various levels of relative humidity.
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Moisture Content vs. Relative Humidity |
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Relative Humidity |
Moisture Content |
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0 |
0 |
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25 |
5 |
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50 |
9 |
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75 |
14 |
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99 |
23-30 |
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 damage 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 some situations, confirmation that these methods have been used will require invasive measures which lie beyond the scope of the General Home Inspection. This should be clearly stated in Home Inspection contracts.
Chinking
Chinking acts as a barrier to air movement through the wall, minimizing heat loss and keeping insects out. Chinking is mainly affected by two forces...
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Ultra violet damage. Flexible chinking, similar to caulk, may be degraded by the ultraviolet (UV) rays of the sun. Modern chinking is designed to minimize this problem, but in evaluating the chinking in any log home it's a good idea to look carefully for signs of UV damage such as cracking or flaking.
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Thermal expansion and contraction. This is an especially common problem in older homes with grout or mortar-based (cementicious) chinking because this type of chinking is brittle. With changes in temperature, logs expand and contract at a rate different from that of cementicious chinking. Over time, this results in deteriorated adhesion between logs and chinking. Chinking may adhere in some areas and not in others, which results in cracking of the chinking. Look for cracking and separation between chinking and logs.
Log Building Standards
These standards have been developed to set minimum guidelines for log home construction. They are worth taking the time to read. In addition to the Log Building Standards and the Chinking Standards much information on Handcrafted log homes can be found at the web site for the International Log Builders Association (ILBA).
The International Log Builders Association is the organization most closely associated with handcrafted log homes. They have developed Building Standards and Chinking Standards and their website contains a great deal of useful information.
MANUFACTURED LOG HOMES
Manufactured log homes are built using logs which have been milled to a uniform diameter and shape. Logs usually have a profile milled into the top and bottom which allows each log to interlock with those in the course above and below. Interlocking profiles 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 while retaining the log look at the exterior.
When milled logs have no interlocking profile they're sometimes milled with a rounded groove on one side. This type of profile is often called "Swedish Cope". This term can be confusing because cutting a scribed log is sometimes called "coping" the log.
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Swedish Cope
More information on manufactured log homes can be found at the web site for the Log Homes Council http://www.loghomes.org/
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.
Log Extensions
Exterior log extensions should be self-draining and should fit tightly. They should be a minimum of 9" long, but the maximum length is determined by the length of the roof overhang. Overly long extensions are at high risk of decay. Non-bearing extensions should have air space between courses to encourage moisture to evaporate
INSPECTION of LOG HOMES
Log Home Standards of Practice
Although Standards of Practice are now under development by the International Association of Certified Home Inspectors (InterNACHI), no Standards of Practice for inspecting log homes have been established as of year's end 2007.
Limitations of Log Home Inspections
Log homes have been and continue to be constructed using many different methods. The nature of some of these methods often 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.
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.
I'm the author of the comprehensive, online Log Home Inspection course. This course is free to the public and covers everything from living trees to log finish coatings. Please feel free to take the course.
Sources of information on log homes:
GENERAL INFORMATION
ILBA Log Building Standards
The Log Building Standards are crucial reading for those inspecting log homes.
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