May, 2019

Inspection News and Views from the American Society of Home Inspectors

Inspecting Log Homes


This year marks my 15th year as an ASHI inspector. 

I’m a second-generation inspector and ASHI member. My father, Bob Anderson, ACI, and 2018 Cox Award winner, was an advocate for ASHI and the stellar education it offers. He urged me to join ASHI years ago and thus began my journey with this fine society. 

Living in Virginia has afforded me many opportunities to inspect unique properties, including homes built in the early 1700s and homes owned by Thomas Jefferson. Out-of-the-box inspecting is normal here. 

One type of construction in Virginia is the log home. For me, stepping foot into a log home feels a bit like coming home—the warmth and coziness of the construction floods over me like a handmade quilt. My love for log homes started in 2001 when my father and I inspected a log home built in 1750 in Waynesboro, VA. The hand-hewn logs connected with mortise and tenon joinery, all notched and labeled with Roman numerals at the connections, made for a very memorable experience!

I hope you’ll get the opportunity to inspect a log home during your career. I’ve found that it’s helpful to be familiar with some history, basic terminology and common defects to watch for. 

Let’s get started!

Log cabins are usually one-room buildings that were originally used as shelter by settlers and trappers. These shelters were basic, constructed from timber felled from the immediate area This timber was stripped of bark (using a draw knife) and hand-hewn (using adzes and broad axes) to fit and stack. Twigs, straw and wood scraps mixed with mud (called chinking) filled the space between the logs. Log cabins built using these methods have uneven walls, logs and widths between the logs. These cabins were highly susceptible to settlement, moisture and wood-destroying insects.

Historians believe that log cabins were first built in America between 1638 and 1643 in the Swedish colony of Nya Sverige near the Delaware River in what is now New Jersey. The Braman-Nothnagle Log House has been on the National Register of Historic Places since 1976. Log cabins are not unique to America, however; they have been traced to the Bronze Age (about 3500 B.C.) in Northern Europe. 

Today, computer engineering, modern technology and imagination have transformed simple log cabins into masterpieces. Today’s log homes can cost as little as a few thousand dollars to a whopping $40 million! For example, there’s an ultra-expensive, 26,000-square-foot log home marvel, located in Michigan’s Upper Peninsula, that took four years to construct and was designed by 22 architects. 

The love affair with log homes doesn’t stop with adults. Kids are also keen to the idea of building and imagination. In 2016, the building toys “Lincoln Logs” celebrated their 100th anniversary. This classic construction toy was developed by John Lloyd Wright, son of Frank Lloyd Wright, in 1916. 


Log Grading System

How a log is graded: Logs are graded by visual inspection. The strength-altering factors, or “defects,” found during visual inspection result in the assigned grade. Defects include (but are not limited to) checks, compression wood, decay, edge, holes, knots, manufacturing imperfections, slope of grain and splits.

Each grade has an “allowed design stress value,” which is used by engineers to choose the appropriate species, size and grade of log for the application being considered. This system is also used by local code officials to assure them that the logs meet building code requirements.

What are the grades and what do they mean? Timber Products Inspection (, a national grading agency, established a grading program that indicates grade restrictions for each grade of wall logs. The grades are from highest to lowest: Premium, Select, Rustic, Wall Log 40, Wall Log 30 and Wall Log 27.

“Slope of grain” is one of the restrictions used when determining the grade. Slope of grain is the degree of twist evident in the log, which is measured by determining the amount of grain twist in a given distance down the length of the log. For example, a slope of 1 in 12 means the grain moved away from the axis of the log 1 inch over a distance of 12 inches.

Using this factor as an example of the progressive relaxation of the restriction, you’ll find the following pattern: In a Premium grade log, the restriction for slope of grain is 1 in 12; however, in a low-grade log, Wall Log 30, the grade is 1 in 5.

Because slope of grain measures the twist that developed in the log while it was alive and growing, it does, in effect, predict the level of risk that the log will “untwist” and the degree to which it will untwist. A slope of grain of 1 in 12 indicates a low risk that the log will untwist and, if it does, the movement will be minimal. On the other hand, a slope of grain of 1 in 5 indicates a higher likeliness to untwist and the chance that the log will move considerably while doing so. If a log like this is in the middle of your living room’s great wall, the movement may cause unwanted settlement, opening of butt joints and potential for leaks. 

Energy Efficiency

The R-Value of logs: A material’s thermal resistance or resistance to heat flow is measured by its R-value. In a solid log wall, the logs provide both structure and insulation. The R-value for wood ranges between 1.41 per inch (2.54 cm) for most softwoods and 0.71 for most hardwoods. Ignoring the benefits of the thermal mass, a 6-inch (15.24-cm) softwood log wall has an R-value of just over 8 for a clear-wall (that is, a wall without windows or doors).

Compared with a conventional wood stud wall (with 3½ inches [8.89 cm] of insulation, sheathing and wallboard, for a total R-value of about R-14), the log wall is apparently a far inferior insulation system. Based only on this, log walls do not satisfy most building code energy standards. However, to what extent a log building interacts with its surroundings depends greatly on the climate. Because of the log’s heat storage capability, its large mass may result in better overall energy efficiency in some climates than in others.

Logs act like “thermal batteries” or “thermal mass” and can, under the right circumstances, store heat during the day and gradually release it at night. This generally increases the apparent R-value of a log by 0.1 per inch of thickness in mild, sunny climates that have a substantial temperature swing from day to night. Such climates generally exist in the Earth’s temperate zones between the 15th and 40th parallels (Source:

Contractors generally use several types of logs to construct the load-bearing walls of a log home.

Kiln-dried logs: Logs from trees that have been felled, bark removed, cut into proper lengths and placed in a kiln to remove moisture at around 6% to 10%. Most of today’s modern log homes are constructed using kiln-dried wood. Almost all kit-style log homes are constructed using kiln-dried logs.

Green wood: Technically, any wood above fiber saturation moisture content (28%) is considered green, regardless of the time since it has been cut or milled. 

Green logs: These are logs from trees that have been felled and installed shortly thereafter (often within weeks or days). These logs are highest in moisture content and have generally not been treated for wood-destroying insects. 

Dead-standing logs: Trees that have died naturally and remain standing until felled for use. These logs have a slightly lower moisture content (18%-20%) than that of green logs, but higher than kiln-dried logs. This method of log harvest is rare; however, some log companies build homes strictly with these logs (for example, Satterwhite Log Homes).

Air-dried logs: These logs are felled, graded, sorted and cut, then stacked in the open (with overhead cover) with spaces between the logs to allow air flow. The drying process takes 6 to 18 months to complete, depending on the regional humidity. This time allows the log to reach its moisture equilibrium of approximately 10% to 18%. 

Special considerations for green logs: Over a short time, green logs will reduce in size (both in length and diameter). This can be problematic if, during construction, these variances have not been worked into construction plans. As an example, on average, a 10- to 12-foot green log wall can shrink 5 to 10 inches during the process of drying and settlement. 

The log home contractor should account for these potential movements and build in safeguards to prevent structural failure. Oftentimes, the contractor will add a space above doors and windows to allow for the “green” wall to settle and shrink, and not pose a threat to these areas. A door or window that does not have these variances built in can stick, bow and, in extreme cases, break. 

Screw Jacks

Center beams and vertical-center posts or beams will often contain screw jacks at the connections and load-bearing points. These are in place to adjust for movement in walls and shrinkage in logs. Oftentimes, these screw jacks are hidden or concealed to improve the wall’s cosmetic appearance. 

Posts that support upper floors, lofts and roof outcroppings are great places to look for these screw jacks. I’ve personally found them near the sill plate in the basement, but they can be located at the base or top of a post. These screw jacks should not be loose to touch or altered in any way. Defects to screw jacks include added shims, removed jacks, broken jacks, welded sections and noticeable field repairs to the jacks. Report any alterations to the screw jacks that are visible. 


Settlement is a natural process in log homes. Throughout the seasons, the logs will expand and contract according to the climate in the geographical location. Often in rainy and high-humidity areas of the country, the climate can change the equilibrium of the logs, which will allow the logs to retain more moisture than in other areas of the country. 

If you are inspecting a newly constructed log home, it is important to inform your clients that settlement will happen and that it is normal. It is important that the log home builder has added some allowances for movement and settlement. It might be helpful to explain that screw jacks allow the log walls and posts to move without causing any structural fatigue. 


Moisture is one of the greatest threats to a log home. Because the house is built with logs, the wood has a natural capillary effect when water is introduced. Even though the log is dead, its natural ability to draw in water remains active and alive. The ends of the logs are some of the most vulnerable points in a log wall because they are often exposed to the elements and may extend past the roof overhang. As a result, you should spend some quality time inspecting the “log ends” (that is, the corners of the home) during your inspection. 

When inspecting a log end, you should pay attention to the checking in wood. Upward-facing checking (either at the log end or the in-log field) can be problematic, as water can enter the top of the log and be directed toward the center of the log. Once the water enters the check, it travels to the center of the log, and rot and deterioration will begin from within. Repairing log ends can be costly and the cost to replace log ends can range from $400 to $800 (or more) per log. Repairing a log within the field can cost even more than this estimate.

Other areas to look for moisture penetration:
Windows are common areas of moisture penetration and a great area to spend time during your inspection. Look for any staining at the base of the window stool and the butt joints below the window. A standard moisture meter with a probe is an essential tool for inspecting
these areas.

Butt joints in the field: Moisture has the potential to enter the log home through the butt joint during wind-driven rains. Look for signs of moisture penetration inside the home at all joints. Moisture can be identified easily by dark streaks at and below the joints. 

First course of logs:
Often, log homes do not have gutters or downspouts installed. As a result, water from the roof hits the ground and splashes back onto the house and the first course of logs. You should thoroughly inspect log ends, butt joints and checks on the lowest course of logs.

Penetrations in logs: Test for moisture in all areas where pipes, wires or any added penetration is visible. These areas often are sealed with caulking and can separate over time, allowing an opening for moisture. 

Flashing around chimneys and dormers:
These are high-priority areas for inspection and often points of interest regarding moisture penetration. Most log home owners want stone or stone veneer chimneys that are difficult to flash around, which can lead to moisture penetration. Also, some chimneys on the outside of the great or tall log wall can wick moisture into the dwelling via the butt joints. Pay special attention to these areas during your inspection. 



Once you know the common problem areas to look for in a log home, you will be better equipped to inspect the home with confidence. A log home is living and breathing, and it requires continual love and care. The more it is loved, the happier it will be. Contact your local log home contractor or log home restoration company for even more useful, region-specific information. 

Bronson Anderson ACI, is a second-generation inspector and ASHI member. He is the owner of Inspector Homes, Inc., in Waynesboro, VA. He is licensed through the Commonwealth of Virginia as a home inspector, with a New Residential Construction endorsement. Having built log homes himself, he inspects historic log homes for the state and historical preservation organizations. Anderson also co-created a class for real estate agents regarding home inspections in Virginia. He is a former team and squad leader in the U.S. Army Infantry and has had tours in Afghanistan. Bronson joined ASHI in 2003, has served on ASHI’s Council of Representatives, and has been a Council Group Leader and a CRC member. He is the founder and chair of the ASHI Young Professionals task force. He is a past-president of the Central Virginia and Blue Ridge Chapters of ASHI, and a current member of the ASHI Board of Directors (2018-2020) and a trustee of the ASHI Foundation. He is the Board Liaison for the Education committee and ASHI Reporter Task Force Chair.