Cause, Effect, & Dealing with Log Shrinkage in Solid or Milled Log Homes
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Shrinkage in solid logs used to construct both antique and modern log houses produces some special challenges to the builders of those homes. Shrinkage produces not only checking (large cracks that are normal and are not necessarily a problem) but also an actual reduction in log diameter which can, in extreme cases, mean that a wall may shrink in height by an inch or more after construction. A tall log wall like the one in our page to photo may shrink two inches over its height during the first year or year and a half after the building has been closed-in and heat turned on.

Even factory-milled kiln-dried logs may vary in moisture, or they may pick up moisture during transport and storage at the building site. Construction details such as the means of fastening each log course in place and the framing and construction of windows and doors need to take into account this natural movement and log shrinkage that occurs especially over the first 18 months after construction of a new log home.

This series of articles provides information on the inspection and diagnosis of damage to new and older log homes and includes description of log house and log siding insulation values and alternatives, and also a description of the characteristics of slab-sided log homes as well as all other types of log home construction. We include illustrations of log structures from several very different areas and climates in both the United States and Norway. Our page top photo shows a modern kit log home constructed in New York State.

For modern kit and factory-sourced log structures we include details of common construction and building defects that cause water and air leaks and ultimately rot damage and we point to key problem areas that need to be inspected carefully when buying or maintaining a log home.

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An Owner-Builder's Guide to Shrinkage In Log Home Walls

Log homes will shrink considerably in wall height as the logs dry during the first one or two years after construction. This is so even in factory cut "dry" logs which may have absorbed moisture in transit or on site, and it is even more true if the logs used in construction were "air dried" or were used while still "green".

The more moisture that was present in logs at the time of construction of a log home, the greater the amount of shrinkage that will occur in overall wall height, and the larger and more extensive will be the checking cracks that occur in log walls.

Log Checking or Splitting - Are Log or Beam Splits A Structural Concern?

Log checking, long horizontal splits in the log surfaces, will appear on both inside and outside surfaces of log walls and may vary considerably in width (hairline to 1/2") and length (a few inches to several feet). (Photo courtesy Arlene Puentes.)

Checks in logs (or other large timbers) are rarely a structural concern, but they may become a leak or rot problem.

Checks are only a cosmetic concern unless they are taking in water and therefore risking leaks into the building interior or causing rot or inviting insect damage, as we discuss below

See Log Checking or Splitting for additional details about splits and checks in log buildings.

Interior Condensation and Moisture During Log Home Curing

Considerable moisture may be released during the first year or two after construction of a log home, after the home is totally enclosed and central heating / air conditioning have been installed. Our photo (left) shows frozen condensation on a log cabin window overlooking Lake Superior (Two Harbors, MN). Log moisture content is easy to measure using any of several types of moisture meter. Log moisture measurements can help determine whether the condensation seen in a log home is coming from the logs as they cure, from leaks, or from some other moisture source. We discuss log moisture content, green logs, air dried and kiln dried logs, and avoiding log splitting problems on log houses at Log Checking or Splitting. These same factors affect the level of indoor condensation in a building in the first year or two after construction has been completed and the building is fully enclosed.

Log Wall Height Changes During Log Curing

Log walls can shrink up to several inches in overall height during curing, depending on how much moisture was in the logs when the home was constructed. There may also be some seasonal changes in the height of a log wall as ambient moisture varies and as heating or air conditioning are used in the home.

Modern log homes use construction details and log fasteners designed to permit this log shrinkage movement without damage to other rigid building components like windows, doors, plumbing, electrical wiring, and fixtures.

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LOG HOME ENERGY EFFICIENCY
LOG HOME GUIDE
  Antique & Old Log Cabins
  Cracks, Checking or Splitting Beams & Log Homes
  Condensation & Moisture in Log Homes
  Energy Efficiency of Log Homes
  Leak Diagnosis & Cure for Log Houses
  Log Wall Height Changes
  R-VALUES & THERMAL MASS in LOG HOMES
  Sealants, Caulks, & Coatings for Log Homes
  Shrinkage In Log Home Walls
  Slab Log Cabin Siding
  Spline & Gasket Designs for Log Buildings
  Spline Gaps & Gasket Omissions
  Types of Log Houses - Log Choices
  Vertical Log Walls on Cabins & Homes
  Wall Insulation Values in Log Homes
LOG HOME WALL INSULATION VALUES

• Thanks to Arlene Puentes for the photograph of a checked log in a log home exterior. Arlene Puentes, a licensed home inspector, educator, and building failures researcher in Kingston, NY. Photographs © Arlene Puentes 2006 All Rights Reserved. Text © Daniel Friedman Arlene Puentes 2008 All Rights Reserved.
• "The Logless Log Home," Jim Robbins, New York Times, 05/05/2010 Home section, p. D1 & D6.
• "Shop Talk," Martin Mintz, AIA, Builder Magazine, April 1986, detailed solutions for log shrinkage movement by using a "T" jamb at windows and doors. A January 1986 Builder Magazine article shows window installation details in 8" thick log walls.
• "Caulking, Chinking, Insulators, Sealants - which System works Best," Log Home and Alternative Housing Builder, Nov-Dec 1983.
• Lincoln Log Homes Marketing, Inc., 6000 Lumber Lane, Kannapolis NC 28081 704-932-6151
• Insulating Characteristics of log homes were neatly summarized by Roger Rawlings in "Log Homes in a New Light," Rodale's New Shelter, April 1983, p. 28

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