One thing we know for sure at the Forest Products Laboratory (FPL) is that wood and water don’t mix, and keeping wood dry is essential to long service life. So really, 80 years seems like a good, long life for a log cabin built with untreated logs, situated just 10 meters from a river in an area with high snowfall, and subjected to the subsequent spring melting that follows each winter. For this cabin, maintained by Michigan Technological University’s School of Forest Resources and Environmental Science, staying dry has been nearly impossible.
Situated on the north branch of the Otter River in the Portage Township of Upper Michigan, the cabin was built in 1934-1935 by the Civilian Conservation Corps and housed workers who used the site as a trout hatchery. In 1955, it was transferred to Michigan Tech with promise that public rights of hunting, fishing, and trapping would be maintained. Over the years, continuous maintenance was needed due to periodic flooding and the resulting log deterioration.
Since 1998, Michigan Tech and FPL have cooperated to conduct periodic inspections of the cabin. The latest inspection, completed in 2013, utilized various techniques to analyze the condition of the log cabin.
Visual inspection is the simplest method for locating deterioration. Here, researchers look specifically for evidence of water intrusion and damage, especially near the foundation, and evidence of structural failure of the timbers. Many of the logs showed signs of severe deterioration, with the ends of several having been entirely destroyed.
Sound transmission measures the time it takes for stress waves to travel between sensors placed on opposite sides of a timber. Significantly longer transmission times, relative to the base times known for several species, indicate the presence of deteriorated wood. Nearly half of the tested logs produced results in the ‘deteriorated’ or ‘severely deteriorated’ range.
Micro-drilling resistance is a commercially developed technique based on the underlying premise that degraded wood is relatively soft and will have low resistance to drill penetration. Researchers conducted micro-drilling resistance tests in areas of the timbers they believed contained decayed wood based on results from the visual assessments and stress-wave testing. Test results showed that many logs were deteriorated, with most having an outer shell of solid material but a severely degraded core.
In the end, these test results showed that water had finally won the war over wood. Researchers recommended the cabin be dismantled, salvaging any possible historic materials (hardware and any sound timber), and suggested a smaller structure be built on the site using the salvaged materials where appropriate.
For more information on the project, see this FPL Research Note.