The Importance of Log Moisture
Tuesday, September 24th, 2013 | Uncategorized | 3 Comments
In a recent meeting with a business associate he asked questions about our business, trying to get a better understanding of what we do. Although he has little knowledge or experience in the log home business he asked a very interesting question. It was very interesting because, after almost thirty years in the business having done more than 3,000 new log home projects and over 600 log home restorations, he is only the third person to ask that question of me. He asked me if the logs were dry! It was also interesting because in my judgment there is no more important issue related to log homes than the moisture content of the logs.
In almost every one of the restoration projects we have completed some aspect of the restoration was the direct result of the use of green, unseasoned logs when the house was built. In some, significant checking had occurred allowing water, snow and ice to accumulate eventually resulting in wood rot. In others, bowing, crooking, twisting and even splitting had occurred causing the home’s cosmetic appeal to suffer. Only in one case have we ever seen bowing so severe that the structural integrity was in question. Most often and most prevalent was the shrinkage that had occurred resulting in gaps allowing air and water infiltration, which in turn resulted in significant energy inefficiency.
All of this results in expensive restoration being required and almost all of this can be avoided if dry logs are used to begin with. Unfortunately, few log home manufacturers offer dry logs, dried to 19% moisture content or lower. Only about 20% of all manufacturers grade their logs under the auspices of a recognized independent grading agency and only about 2% grade their logs as “Dry.”
Although it is rare for a prospective customer to question if the logs are dry it is quite common for them to ask if the logs are kiln dried. Kiln drying is merely one of the methods used to reduce moisture content. Air drying and the use of standing dead logs are also common methods used to provide logs with reduced moisture content. However, the relevant issue is not which method is used to reduce moisture, but rather how much moisture was removed. The richer question that every prospective customer should ask is, what is the moisture content at the time the logs are delivered to the job site and can you certify that by affixing the appropriate grading agency’s dry grade stamp or letter of certification. A dry grade stamp can only be affixed to logs that are 19% or lower in moisture content.
What is the pertinence of this issue of moisture content? Well, it’s pretty simple, the closer the log is to the average ambient moisture content of the environment it is placed in the less likely an unwanted development will occur. Put another way, the closer the log’s moisture content is to the environment’s moisture content the more predictable the log’s performance will be and vice versa. What the owner of a log home wants is a highly predictable log that he can expect will not develop unwanted conditions after the home is built. If the moisture content of a log is high when the house is built it is virtually impossible to predict what the logs might do as they dry in the erected house. The one exception to this is it is 100% predictable that the logs will shrink and the least that will happen is an undesirable cosmetic condition will develop.
Given the problems that a high moisture content can bring to log homes, I am amazed that those planning log homes are not more knowledgeable about this issue.
More pointedly why don’t more log home companies alert possible customers to the problems and do something about it? All log home companies that have sold more than a few homes with green logs certainly know of the problem. Yet they continue to sell the same problematic materials.
I believe many prospective log home customers use the term “kiln drying” because they have read of it in log home advertisements. I am not so sure that kiln drying, in the truest sense, should be considered when dealing with heavy timbers and logs.
A brief description of wood drying may help illustrate why I think this way.
These days most lumber sold in stores has been kiln dried to assure that after construction the wood won’t significantly shrink or warp. Sometimes the wood is air dried before going into the kiln to reduce kiln costs. To air dry wood it is stacked loosely in layers, with spacers between each layer so that the air can move freely around all sides of the lumber. Once in the kiln the wood is stacked the same way.
There are several different kinds of kiln processes used to dry lumber, with different controls on how long the wood is air dried beforehand and, once the wood is in the kiln, controls of the maximum temperature and relative humidity. Of course the species of wood must be considered in this process, some species taking longer and more care than others to achieve desirable results.
Without a kiln drying process two-inch-thick lumber needs months to air dry to reach a stable moisture content. The same lumber could be suitably dried in a kiln in only a few days or less, depending on the type of kiln drying process.
Now consider logs, and for this example unseasoned wood milled to 8″ diameter shapes. I have been told by a college professor that this size wood in Southern Yellow Pine would take about eight years stacked like lumber to reach a stable moisture content. And larger shapes would take even longer. I did not discuss Eastern White Pine at the time, but I would imagine this species would take a bit less time because it is softer and easier to work with at the start.
When I compare the time to air dry and kiln dry two-inch-thick lumber, the eight years to air dry a log would mean the wood would have to be in a kiln for several weeks. I doubt many log home companies can afford the expense required to provide the size of kilns needed, the time to dry sufficient numbers of logs for a continuing supply of house packages, and the material storage, movement and planning to do all this–at least without greatly increasing prices to remain profitable.
If there are some companies that do this, I apologize. But I suspect the reality is that most references to “kiln drying” logs are only references, with the logs going through some limited drying process so they can be labeled “kiln dried”.
I would advise a log home customer to look for sources of logs that are either from standing dead timber, wood not green usually for a number of years; or laminated logs, made of truly kiln dried two-inch-lumber that has been glued together to form the larger shape.
Tom Garber, not an expert but with 35 years in wood construction, including common lumber, timbers and logs.
Given the problems that a high moisture content can bring to log homes, I am amazed that those planning log homes are not more knowledgeable about this issue.
More pointedly why don’t more log home companies alert possible customers to the problems and do something about it? All log home companies that have sold more than a few homes with green logs certainly know of the problem. Yet they continue to sell the same problematic materials.
I believe many prospective log home customers use the term “kiln drying” because they have read of it in log home advertisements. I am not so sure that kiln drying, in the truest sense, should be considered when dealing with heavy timbers and logs.
A brief description of wood drying may help illustrate why I think this way.
These days most lumber sold in stores has been kiln dried to assure that after construction the wood won’t significantly shrink or warp. Sometimes the wood is air dried before going into the kiln to reduce kiln costs. To air dry wood it is stacked loosely in layers, with spacers between each layer so that the air can move freely around all sides of the lumber. Once in the kiln the wood is stacked the same way and air is usually forced between the layers by fans.
There are several different kinds of kiln processes used to dry lumber, with different controls on how long the wood is air dried beforehand and, once the wood is in the kiln, controls of the maximum temperature and relative humidity. Of course the species of wood must be considered in this process, some species taking longer and more care than others to achieve desirable results.
Without a kiln drying process two-inch-thick lumber needs months to air dry to reach a stable moisture content. The same lumber could be suitably dried in a kiln in only a few days or less, depending on the type of kiln drying process.
Now consider logs, and for this example unseasoned wood milled to 8″ diameter, say 10 feet long. I have been told by a college professor of forestry that to air dry this size log to reach a stable moisture content would take about eight years. And larger diameter logs would take even longer. I expect there would be plus or minus a small percentage of the eight years, based on the species of wood that was to be air dried.
When I compare the time to air dry and kiln dry two-inch-thick lumber, the eight years to air dry a log would mean the wood would have to be in a kiln for several weeks. I doubt many log home companies can afford the expense required to provide the size of kilns needed, the time to dry sufficient numbers of logs for a continuing supply of house packages, and the material storage, movement and planning to do all this–at least without greatly increasing prices to remain profitable.
If there are some companies that do this, I apologize. But I suspect the reality is that most references to “kiln drying” logs are only references, with the logs going through some limited drying process so they can be labeled “kiln dried”.
I would advise a log home customer to look for sources of logs that are either from standing dead timber, wood not green usually for a number of years; or laminated logs, made of truly kiln dried two-inch-lumber planks that have been glued together to form the larger shape.
Tom Garber, not an expert but with 35 years in wood construction, including common lumber, timbers and logs.
Tom,
Your comments were very interesting and insightful, particularly the point concerning the industry’s less than forthright posture relative to the issues surrounding moisture content and the practice of putting logs in a kiln in order to label them as kiln dried.
Putting logs in a kiln doesn’t say anything about their resultant moisture content. It simple says they were in a kiln. I can relate an experience I had years ago when visiting a competitor’s mill. He had a couple of large barn buildings painted black with large fans blowing air across the logs then professing he sold kiln dried logs.
The bottom line is, if the logs are not graded and stamped with a “dry” stamp you won’t know what the moisture content is. They might be dry or they might be saturated! Appreciate your comments.
Len Kroll