J6 - Bearskin Cabin Insp Rpt.pdf

CONDITION ASSESSMENT OF THE SUPERIOR NATIONAL

FOREST EAST BEARSKIN LAKE LOG GUARD CABIN

By:

Brian K. Brashaw, Program Director Robert J. Vatalaro, Principal Research Shop Foreman and Steve Schmieding, USDA Forest Products Laboratory

March 2007 USDA Forest Service Project No. 187-6572 Superior National Forest NRRI/TR-2007/04 8901 Grand Ave Place

Duluth, MN 55808 Natural Resources Research Institute University of Minnesota Duluth 5013 Miller Trunk Highway Duluth, MN 55811

SUMMARY

A condition assessment inspection was completed on the East Bearskin Lake log guard cabin in October 2005. This inspection was completed by University of Minnesota Duluth staff and documented by a photographer from the USDA Forest Service Forest Products Laboratory. Several staff members from the Superior National Forest participated in a review of inspection techniques and equipment. They were present for approximately 4 hours during the inspection. The cabin was inspected using a combination of visual inspection techniques, hammer sounding, stress wave timing and resistance microdrilling. Detailed results of the inspection are provided in the report.

There was visible decay present on the lower log ends, log corners and sill logs. This decay should be addressed through accepted log restoration techniques. This may include patching, wooden plugs, wood preservative, insecticides, replacement of ends, half-logs or full logs. This includes logs on the cabin front above and below the porch screens and door, the cabin left and right sides and the rear of the cabin. The most significant problems were identified on the cabin rear, most likely caused by water from the kitchen sink, and close contact with the ground. A strategy should be developed for the roof drip zone around the cabin. Significant splashback is occurring, wetting the lower cabin logs, log ends and log corners. This water increases the moisture content of the logs, leading to decay in these locations. Decay and insect damage was noted in the inside main ridge beam near the interior log wall. This must be further investigated, since there was no access to the beam behind the wall. A 4.5 inch diameter section of this log is damaged. The source of moisture needs to be identified and removed. A treatment and repair plan should be developed.

OBJECTIVE

The objective of this project was to conduct an inspection and condition assessment of the East Bearskin Lake log cabin, owned by the USDA Forest Service, Superior National Forest. The inspection will be used as a case study for technology transfer of inspection methods for historic wood structures through hands on training of Forest Service personnel and through a web based seminar in 2007.

BACKGROUND

Since 1995, the USDA Forest Products Laboratory (FPL) has worked cooperatively with the American Society of Civil Engineers (ASCE) and other cooperators (University of Minnesota Duluth, Washington State University, Forest Products Society) to develop and teach a short course on inspection of structures. ASCE has taken the lead by providing overall coordination of these efforts and scheduling and marketing support.

FPS has provided technical literature, including the recently published “Wood and Timber Condition Assessment Manual”. The resulting course has been presented over 100 times throughout the United States with over one thousand attendees.

As part of our ongoing efforts to further transfer information related to inspection of structures, we are frequently called upon to answer technical questions posed by a wide variety of users. Local municipalities, state and federal agencies, and individuals call on a regular basis asking for help in assessing the in-service condition of wood in their structure.

A grant from the USDA Wood Education & Resource Center and Northern Initiatives was received in 2006 and used to develop electronic technology transfer methods by developing a web portal and through web-based seminars (webinars). A Community of Practice was developed for the Inspection of Historic Wood Structures. This web-based community used a secure web-based platform in the project. This community contains specific tabs or folders for discussion forums, equipment marketplace (includes demonstration videos and links to vendors), library (scientific and technical reports and presentations), webinars, continuing education, e-newsletters, and a calendar. It is a comprehensive web location for professional inspectors, engineers and facility owners and managers.

Our project team conducted inspections of several historic structures during the project period. The inspections included:

• Superior National Forest - East Bearskin Lake cabin; Gunflint Trail, Minnesota

• Ottawa National Forest - inspection of camp/lodges located at Camp Nesbitt;

Kenton, Michigan

• 1894 Hoist House and the Blacksmith Shop of the Keweenaw National Historic

Park, Quincy Mine Unit; Hancock, Michigan

• Cheboygan River Front Range Light Station; Cheboygan, Michigan

• WAPAMA National Historic Landmark, San Francisco National Maritime Park

• Wood-frame construction homes affected by flooding from Hurricane Katrina;

New Orleans, Louisiana

These inspections were completed by members of our project team and our cooperators and served as the basis for the development of technical inspection reports and our webinar series. This report details the results of the Bearskin Lake Cabin owned by the USDA Forest Service, Superior National Forest.

The Bearskin Lake cabin was constructed on the shores of East Bearskin Lake, along the historic Gunflint Trail in northeastern Minnesota. Bearskin Lake serves as an entry point to the Boundary Waters Canoe Area Wilderness. This handcrafted log cabin, constructed in 1935 by the Civilian Conservation Corps, is located outside the wilderness boundaries and is used as a base for summer portage crews, fire crews and other staff as needed. This cabin has been modernized with electricity and running water. It is maintained by the Superior National Forest. Typical visual inspections are used to develop maintenance plans as necessary.

METHODS

Three widely-used methods were utilized to assess the condition of the wood members in the log cabin. Detailed information on these techniques can be accessed at the web portal developed for this project, http://qp.ntht.org/historicwoodstructures. They were:

Wood species identification Small wood samples were collected from several of the log members. The samples were then sent to the USDA Forest Product Laboratory (FPL) for species identification.

Visual inspection An extensive visual examination of the structure was performed. In particular, we looked for any evidence of fungal growth such as insect damage, fruiting bodies, brown crumbly wood, or evidence of exposure to water. As part of the visual inspection, we used hammers as part of a sounding test. This low impact allows inspectors to identify areas that have a different audible response to a hammer. For instance, a decayed log will have a distinctly different sound than a solid log. Sounding can also help identify loose connectors and agitate insects that are present.

Ultrasound/stress wave testing It has been shown from extensive research studies that deteriorated wood transmits stress waves or ultrasound in a manner that is significantly different than that of non-degraded wood. Specimens with a high stress wave speed are generally in higher quality than those with low stress wave speeds. Stress wave timing tests were conducted, perpendicular to the grain, at most all wall locations in the structure, with specific attention to those areas that showed visual evidence of decay, insect damage, or evidence of moisture. The testing was conducted by using several types of commercially available stress wave timers. A Fakopp microsecond timer and a Sylvatest Duo were used in the inspection. Both pieces of equipment provide similar stress wave test results for both solid and decayed wood.

Resistance micro-drilling Mechanical probing type tests are also useful for locating deteriorated wood. An automated drilling device was used in this inspection. A steel drilling bit penetrates the wood at a uniform speed while drilling resistance is measured. The measured resistance data (recorded on a 0-100% scale) is recorded on a wax paper strip at a scale of 1:1 and can be captured electronically for downloading to a personal computer.

Measured resistances could be used to differentiate wood with deterioration from sound wood. The drilling bit has a small diameter, causing minimal damage to the material. An IML Resistograph F300 was used during this inspection.

RESULTS

Wood species identification The species of the log members used to build the cabin was determined to be spruce (Picea spp). It was not determined which species, although it is thought to be white spruce. Samples were taken from several inconspicuous log locations on the inside of the cabin.

Visual inspection A visual inspection of the log cabin interior and exterior noted several locations of decay, insect infestation, water damage and bird damage. Figures 1-4 show the specific locations of the damage noted on each side of the building and figures 5-12 show close-up areas of damage. The cabin is identified by noting the front had a porch entrance and the rear had a kitchen entrance. The cabin sides were noted as right and left as a person would enter the front porch. Visible decay was present on log ends and log corners around the cabin. It was often located on the lowest log, which was located within 6-10 inches of the ground. These logs receive backsplash from the ground and often had vegetation in near contact. A section was noted on the left side of the cabin where firewood had been stacked in direct contact, providing moisture and insect access points. Several sections of the lower sill logs contained significant insect damage from various types of beetles. There was also log decay noted along the screen windows on the front porch, where moisture entered the logs.

The inside of the cabin was also inspected visually. The only visual indication of damage was fine wood residue caused by insects on one section of the main ridge beam. This is shown in figure 13.

Figure 1.--Front left cabin with visual damage noted in red circles.

Figure 2.--Rear section of log cabin. No visual damage was noted.

Figure 3.--Right side section of log cabin with visual damage noted in red.

Figure 4.--Left side of Bearskin cabin with visual damage noted in red circles.

Figure 5.--Close-up of damage on left side of cabin with decay and insect damage located on bottom log and the exposed log ends.

Figure 6.--Damage to logs ends from nesting birds along left side of cabin.

Figure 7.--Left side log corner decay.

Figure 8.--Decay present along left side under screen window on porch.

Figure 9.--Beetle damage to sill log along left side of cabin.

Figure 10.--Beetle damage on sill log on cabin front to right of front steps.

Figure 11.--Decay sections on front log corner.

Figure 12.--Decay and log damage on front right log corner.

Figure 13.--Insect damage noted on main ridge beam by evidence of fine wood sawdust.

Ultrasound/stress wave testing and resistance microdrilling

Stress wave inspections were conducted on all log sections of the cabin. This testing is completed through the cross-section of the log. Each exposed log end or corner was inspected. Each cabin wall log was also tested at various locations in an effort to locate decay that was not visually evident. One operator was located outside the cabin and the other on the inside. The cables were run through an open window or door. If decay was noted, the logs were intensively tested to determine the extent and location of the decay. An IML resistance drill was used to confirm the decay in those areas.

Decay was noted in several exposed log corners and ends where decay was not noted during visual inspection. The damage logs were most often those closest to the ground.

We identified hidden decay in several locations on the front of the building and on the rear of the building. The decay on the rear of the building was not visual. The results for each wall (front, rear, left and right) and the interior ridge beam are noted in the following sections.

Figures 14 and 15 shows stress wave timing and resistance microdrilling techniques used in the inspection of the cabin. Two sensors are used in stress wave timing to determine the time it takes for a wave to travel through the logs. Transit times greater than 200 µs/ft are indicators of decay. Resistance drilling values ranging from 0-25% confirm varying levels of decay.

Figure 14.--Fakopp stress wave inspection of log ends.

Figure 15.--Resistance microdrilling of rear wall using an IML resistograph.

Cabin FRONT

Figure 16 shows an overview of the cabin front. The sections of decayed logs identified using stress wave timings and resistance drilling techniques are shown as highlighted in red if they are categorized as substantial decay and yellow as moderate decay.

Figure 16.--Bearskin cabin front showing decayed sections as identified through visual inspection, stress wave timing and resistance drilling. Red shows severe decay and yellow moderate decay.

The stress wave timing data for these sections was inadvertently destroyed, but the resistance drilling confirmed the damage in these locations. Figure 17 shows the resistance drilling data collected from locations 1, 2, 3, and 4 on the log above the porch door. This data shows that there is no internal decay at sections 1 or 4, but that there is a 3 inch diameter decay pocket located above each vertical log at locations 2 and 3.

This was an approximately 10 inch diameter log.

Figure 17.--Resistance microdrilling results from the log above the porch windows.

Decayed sections are shown in red.

Cabin RIGHT SIDE

Figure 18 shows the right side of the cabin. The decayed sections identified through visual, stress wave and resistance drilling showed only two log ends that showed decay.

No decay was located in the wall logs along this side of the cabin as confirmed in the resistance drilling charts shown in Figure 19.

Figure 18.--Decayed sections on the right side of the cabin as located through visual inspection, stress wave timing and resistance micro-drilling. Red is shown as severe decay and yellow as moderate decay.

Figure 19.--Resistance drilling data from right side sill log at various locations.

Cabin LEFT SIDE

Figures 20 and 22 show the left side of the Bearskin guard cabin. The decayed sections identified through visual, stress wave and resistance drilling showed decay present in the front porch log corner and sill log, at the log ends where the main cabin and porch meet, at the other logs ends and the sill log of the main cabin. The red shaded sections show severe decay and the yellow sections show moderate decay.

The sill log with insect damage also contains decay and is shown in red. Resistance drilling data for the sill log is shown in Figure 21 and 23.

Figure 20.--Right side of Bearskin cabin showing decayed logs. The red sections show severe decay.

Figure 21.--Resistance drilling data on the left side sill log at location 1 and 2.

Figure 22.--Right side of Bearskin cabin showing decayed logs. The red sections show severe decay and yellow sections moderate decay.

Figure 23.--Resistance drilling data on the left side sill log at location 1 and 2.

Cabin REAR SIDE

Figures 24 and 25 ABC shows the rear side of the Bearskin guard cabin. There were no visual indications of decay present. The inspection using stress wave timing identified significant levels and areas of decay in the logs under the rear kitchen window. A sink exists in the kitchen and likely water damage to the logs under the window. Figure 24 also shows the stress wave timing data recorded. Stress wave transit times over 200 microseconds (µs) suggest decay and numbers over 400 µs significant decay. One log shows decay present nearly the full width of the cabin.

Figure 24.-- Rear side of Bearskin cabin showing decayed logs. The red sections show severe decay and yellow sections moderate decay.

Inspection of the interior kitchen showed that the sink abutted the 2nd log below the window, which was determined to have severe decay. The water ran off the counter and onto the log. The log just below the floor level also had severe decay, most likely caused by water splashing onto the floor, and entering the log. This is shown clearly in Figure 25. Figure 26 shows the resistance drilling data for the rear wall, data that confirms the significant decay.

A B C

118 626 646 396

369 362

A

B

Figure 25 A, B C.--Left to right close-up of decayed sections identified using stress wave timing.

The red sections show severe decay and yellow sections moderate decay.

107 105 110

750 444 538 198

123 118 112 114 108

147 151 150 157 180

231261306338 362

C

Figure 26.--Kitchen log wall showing water damage. The decay identified through stress wave inspection and resistance drilling is shown in red and yellow shading.

Figure 27.--Resistance drilling data for the rear cabin sill log, since stress wave timing was not able to be completed due to access issues. Decay was noted in several sections.

Figure 28.--Resistance drilling data for the 3rd log up from the ground showing decay. The microseconds noted on the chart correspond to the drilling location as show on Figures 25 A, B and C.

Figure 29.--Resistance drilling data from various locations on rear cabin wall. The microseconds noted on the chart correspond to the drilling location as show on Figures 25 A, B and C.

Cabin INSIDE

Visual inspections, stress wave timing and resistance drilling was also completed inside the cabin on the interior wall and the ridge beam. The presence of decay and insect infestation was noted in the ridge beam, on the inner wall above the space heaters.

Figure 30 shows the damage area with stress wave timing data. Figure 31 shows the resistance drilling data at the two timing locations. No other damage was noted on the visible section of the ridge beam, but we did not have access behind the wall where the damage was present.

Figure 30.--Stress wave and resistance drilling was conducted on the main ridge beam where insect activity was noted. The stress wave data is shown on the picture.

Figure 31.--Resistance drilling conducted at the two stress wave locations. Decay is noted as red for severe and yellow for moderate. Additional testing is recommended for the section behind the wall.

140 µs

380 µs

CONCLUSIONS

Based on the results of the condition assessment of the East Bearskin Log guard cabin, the following conclusions and recommendations are made:

• There is visible decay present on several of the lower log ends, log corners and sill logs. This decay should be addressed through accepted log restoration techniques.

This may include patching, wooden plugs, wood preservative, insecticides, replacement of ends, half-logs or full logs.

• Decay that was not visible was noted to log sections as identified through stress wave timing and resistance drilling. This includes logs on the cabin front above and below the porch screens and door, the cabin left and right sides and the rear of the cabin. The most significant problems were identified on the cabin rear, most likely caused by water from the kitchen sink, and close contact with the ground. This decay should be addressed through accepted log restoration techniques. This may include patching, wooden plugs, wood preservative, insecticides, replacement of ends, half-logs or full logs.

• All firewood should be stored at least 6 ft from the cabin. Firewood was noted placed in direct contact with the cabin. Grasses and vegetation should be mowed regularly to minimize direct contact with the cabin logs.

• A strategy should be developed for the roof drip zone around the cabin. Significant splashback is occurring, wetting the lower cabin logs, log ends and log corners. This water increases the moisture content of the logs, leading to decay in these locations.

• Decay and insect damage was noted in the inside main ridge beam near the interior log wall. This must be further investigated, since there was no access to the beam behind the wall. A 4.5 inch diameter section of this log is damaged. The source of moisture needs to be identified and removed. A treatment and repair plan should be developed.

ACKNOWLEDGMENTS

This project was funded through a grant awarded by Northern Initiatives and the USDA Forest Service Electronic Commons Project. Match funding was provided by Northern Tier High Technology Corridor at Bemidji State University, the Forest Products Society, U.P. Engineers & Architects and the University of Minnesota Duluth.