Micro drilling test on a piling using the IML RESI F300-S - USDA Forest Products Laboratory reportStructural Wood Timber or Beam Damage Assessment
How experts assess the structural integrity of wood framing or wood timbers in-situ using micro-drilling

  • WOOD STRUCTURE ASSESSMENT - CONTENTS: History of Methods Used for Standing Trees & Wood Timber Assessment. Table of features, operating procedures, costs, effectiveness of various methods for standing trees or for wood structural member assessment. CURRENT IN-SITU WOOD BEAM ASSESSMENT METHODS - In-situ Wood Beam, Timber, or other Wood Framing Member Structural Condition Assessment Methods. In situ Timber Assessment
  • POST a QUESTION or READ FAQs about methods used in testing structural wood members for damage or decay & the role of micro-drilling tests for in-situ evaluation of structural wood beams, timbers, or other framing members in buildings..

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Test methods for determining the soundness of wood structural members:

This article series surveys methods used to test & evaluate the structural integrity of wood-framed buildings where focus is on the condition of structural wood posts, beams and other framing members. We discuss the problems surrounding hidden rot or decay, the presence or absence of moisture or other instrument-detectable clues, and the problem of subjective decisions to replace or not-replace suspect wood structural members. Page top image of micro-drilling, USDA FPL [20].

This article compares using micro-drilling with other methods to screen both standing trees and wood structural elements for hidden damage.

The original authors, Probett et als., propose a technique to provide objective pass-fail data on the condition of in-situ but suspect structural wood using micro drilling to examine wood density. This service uses timber resistance drill technology to profile variations in timber density associated with timber decay. The work is done on site and the results are instant.

This technology is objective and evidential in nature and provides assessment as to whether wood is significantly decayed, suspect or suitable for retention.

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Survey & Evaluation of Methods Used for Structural Wood Timber or Beam Assessment

Micro Drilling in-situ timber test - Incodo, Tauranga New ZealandPaul Probett, Clinton Craig, Blake Probett, Incodo Forensic Building Specialists [1]

This article series on methods for assessing structural wood rot & damage is adapted & expanded from the author's "An Introduction to Micro-Drilling Technology for N. Z. Structural Timber Assessment" and is used with permission. We [DF] have added comments, some illustrations, and additional article citations.

At the references section we include a link to the original article as well as contact information for the authors and Incodo Ltd., a Tauranga, New Zealand forensic engineering firm.

[Click to enlarge any image or illustration]

Introduction: A Brief History of Methods Used for Standing Trees & Wood Timber Assessment

A variety of tools and methods for assessing the condition of standing trees as well as the structural integrity of in-use wood timbers & beams has been in use for decades.

Several methods for obtaining drill samples or core samples from standing trees have long been in use by agencies such as the U.S. Forest Service and agencies in other parts of the world as part of evaluating the condition of standing timber and forests. [16] In addition a variety of other methods such as ultrasound, stress waves, electrical resistance testing, mechanical coring or boring, visual inspection, and even a simple plastic hammer have been used to evaluate possible decay or insect damage in both trees and other exposed, accessible wood structural elements.

Methods used initially to evaluate standing timbers were quite naturally expanded to permit assessment of the structural integrity and condition of key wood structural members that are completely exposed and thus readily accessible, such as timber-constructed bridges, bridge pilings, telephone poles, railroad ties, as well as engineered lumber such as block-laminated timbers. [2][3][4][5][6][7][8][9][10]and [19][20][21][22][23]

Collapsing building © Daniel FriedmanThe presence of those tools and methods for testing exposed timbers suggested possible applications in the evaluation of buildings and other structures in which their structural wood members may be partly or even completely hidden by finish materials.

More recently, Bohumil Kasal & Thomas Tannert have led research on the design of microdrilling methods and on the reliability of such tests in predicting the actual bending or breaking strength of structural wood members.

It was Kasal who developed recent technology of taking micro specimens of wood that in turn might be used to obtain direct measurements of the modulus of elasticity and strength of wood (in the area tested).

A direct measurement of the tension properties of wood along the wood fibers permits bending strength evaluation - important because bending strength is a key property in evaluating the structural integrity of a wood beam. Kasal's significant observation was that

... tensile strength has been related to bending strength and is considered to be approximately equal. Tensil properties have a poor correlation with compression properties therefore tensile strength can not be estimated using information attained with the core drilling technique. Specimens can however be extracted to evaluate the tensile properties of in situ members with the technique [described by Kasal]. [5]

Here, in expansion of an original article by Probett et als [1], here we discuss the range of structural wood beam or timber assessment methods where wood beams, timbers, or other structural members are used in buildings and where there is known or suspected risk of structural damage from leaks, decay by wood rotting fungi, or damage by wood destroying insects.

Because Probett et als propose and discuss the applicability of micro-drilling test methods for assessing wood structural members in-situ with or without having to perform more extensive demolition to actually expose the members, special attention is given to this method of structural assessment of wood, including Probett et als' test protocol and progress in evaluating the efficacy of this method.

Photograph of  severe roof structure damage from an unattended roof valley leak in a historic home.Watch out: Important additional research on the efficacy of microdrilling has been conducted in the U.S. by the USDA Forest Products Laboratories by Brian K. Brashaw et als using the IML RESI F300-S.

That 2005 study provides important independent experience and assessment of the micro-drilling approach to structural wood testing.

As you will read in our inserted opinions and warning remarks in the article below, wood testing equipment should not be used by itself to form conclusions about a structure. Excerpting from the Brashaw micro-drilling study conclusions:

It is crucial to use this or any nondestructive testing tool or device as part of a comprehensive condition assessment. Such an assessment should incorporate an in-depth visual inspection, knowledge of prior use of the structure, and a working knowledge of fundamental engineering properties of structural wood products.

This technique, when used in concert with visual and ultrasound techniques, would provide a very accurate description of the condition of timbers. [20]

Why perform in-situ timber or wood structural member assessment?

  • The timber in many New Zealand (NZ) buildings and structures is either untreated, or exposed to conditions beyond that of deigned treatment levels. Structural damage as a result of leaky homes or premature decay or just aging and attack by bacteria, wood-rotting fungi, and insects is widespread.
  • Traditional methods used to determine soundness of timber have been either invasive / destructive to envelopes and interior surfaces or based largely on visual assessments.

In situ Timber Assessment Compared with Other Current Bases for Wood Structural Member Assessment

  • Current basis of most decisions to retain or replace is ‘visual and chisel’ with limited microbiological backup often from “money shot” areas.
  • Replacement decisions are frequently based on a conservative approach i.e. everything within 1.0m from last decay point to be replaced – emphasis is on all degrees of decay replaced. In the absence of better information the approach is considered to have some merit
  • The results tend to be subjective, rather than having been based on objective and evidential data.

These conditions result in two significant error risks:

  1. Failing to repair or replace structural damage that thus risks a costly or injurious building collapse
  2. Repairing or replacing materials that actually are serviceable, resulting in significant and unnecessary costs

In situ Timber Assessment Impact on Government Departments and Local Authorities

Micro Drilling in-situ timber test - Incodo, Tauranga New Zealand
  • Possibility that more framing than strictly necessary is being replaced – impacting on FAP contributions, and Councils in particular when FAP* not pursued.

    * FAP in New Zealand refers to a weatherization Financial Assistance Package provided through the Building & Housing agency of the Ministry of Business, Innovation & Employment. More information about FAP can be found at http://www.dbh.govt.nz/fap
  • Evidence provided by claimant in disputes tends to be opinion based and hard to challenge.
  • Degree of remediation design is determined by early report snapshot findings and assumptions. This tends to lock works into a specific approach – with little opportunity for reclads to be lessened to targeted repairs or partial reclads.*
  • The current absence of a widely available cost effective non-destructive in situ test methodology for timber structural element assessment has limited options for remediation.

* Note Incodo is the original authors' forensic consulting firm. Incodo’s niche is providing building forensic assistance and inspection technology to government departments, consultants and others. Incodo does not undertake remediation project management, remedial design, prepurchase or similar work.


InspectAPedia is an independent publisher of building, environmental, and forensic inspection, diagnosis, and repair information provided free to the public - we have no business nor financial connection with any manufacturer or service provider discussed at our website. 

Current In-situ Wood Beam, Timber, or other Wood Framing Member Structural Condition Assessment Methods

Current choices for assessing the structural integrity of wood timbers, beams, or other framing members include the following:

Each of these approaches to detecting wood beam rot and assessing its extent and its impact on the condition and serviceability of the wood member being examined is discussed and compared in the article segments listed above.

In 2013 Probett et als. presented an update on the status of micro-drilling for wood timber assessment at the U.S. FPL Wisconsin conference: 18th International Nondestructive Testing and Evaluation of Wood Symposium, as we cite below. Significant in Mr. Probett's remarks is

The main advantage of this integration is that when microdrilling and Fractometer testing are done closely together on the same plane of a piece of timber the resultant graphic profiles are very similar so we have two very different test methods crosschecking each other – the key inference is that microdrills are profiling, but not measuring compressive strength parallel to grain, but a digital Fractometer can supply actual compressive strength measurements. [1a][1b][1c]

  • Paul Probett, Clinton Craig, Blake Probett, "In Situ Structural Timber Strength Measurement Advances Using Qualitive Resistography and Quantitive Resisto-Fractometry" [Power Point Presentation] [1.7MB file], Paul Probett Clinton Craig Blake Probett INCODO Ltd, Tauranga, New Zealand, mail2us@incodo.co.nz, Presentation, U.S. Forest Service Conference, Madison Wisconsin, September 2013.

  • Paul S. E. Probett, Clinton S. Craig, Blake In Situ Structural Timber Strength Measurement Advances Using Qualitative Resistography and Quantitive Resisto-FractometryJ. Probett, "" [USFPL paper, 730KB], Paul S. E. Probett MIFPI, AsocRICS, MBOINZ, MNZIBS, NZCB. Clinton S. Craig Blake J. Probett INCODO Ltd, Tauranga, New Zealand, mail2us@incodo.co.nz, 18th International Nondestructive Testing and Evaluation of Wood Symposium - Madison, WI Sept 2013, http://www.forestprod.org/symposium2013/,
    In situ and on site evaluation of timber used for structural purposes has largely been based on methodologies that give qualitive assessments that describe condition aspects, rather than providing measurable “strength” data. This is largely due to the absence of site-friendly equipment and processes that provide the various “strength” values engineers need for meaningful structural evaluation. Even when such methodologies are used, sample size, the degree of destructive investigation and the difficulties in quickly relating ultimate values to yield strength and/or to various local or international code requirements present issues. This document describes a paired methodology based on electronic resistography, used alone and in concert with incremental core type fractometry coupled by using software that permits a high degree of integration of results.
    This is acknowledged to be a starter paper with limitations, based on preliminary and limited research undertaken in house by a very small company, in a remote corner of the globe, undertaken by field technicians looking for solutions to a real experienced problem. It highlights, arguably, a novel direction in this area whereby specific strength characteristics of wooden structural elements can be determined on site. Largely it identifies tools and methodologies with a strong emphasis on site applications. Keywords: digital Resistograph, digital Fractometer, fractometry, resisto-fractometry, control tests, yield strength, Woodchecker, in situ, on-site, timber strength.


Additional Wood Decay or Damage Testing Instruments / Methods

Bob Monk, USDA Forest Service, discussed the use of various types of equipment capable of detecting decay in standing trees - the epitome of in-situ testing. Monk described and tested an extensive list of tools and methods for assessing the condition of trees, possibly also used for structural wood member evaluation. Monk's USDA article expands upon the types of options and test instrument applications discussed here. The following table of tree decay detection equipment is adapted from Mr. Monk's USDA article [16] - DF

Table of Tree Decay Detection Equipment

Equipment Type & Basic Properties Wood Test Tool Name Wood Test Tool Cost $USD Manufacturer / Source

Ultrasonic wood decay detection

A sound wave is transmitted through the wood to a receiver; decayed wood slows the stress-wave signal. Stress waves vary by wood species. This approach permits multiple readings (for free-standing readily-accessible timbers or of course, for trees) thus permitting a 2-D map of the extent and location of wood decay. Limited to 1m of thickness; errors arise if sensors not properly placed. Early decay hard to spot.

Arborsonic Decay Detector $3,000. Fujikura Europe, England
James "V" Meter $2,650. James Instruments, Chicago, IL
Sylvatest n/a Sandes SA, Switzerland
FAKOPP Ultrasonic Timer $2,580. FAKOPP Ent., Hungary
Picus Sonic Tomograph
(12 sensors + software)
$18,000. Fujikura Europe, England

Stress Wave Timer wood decay detection

Similar to Ultrasonic method above, using a lower frequency signal generated by a tap-hammer. Can handle larger diameter trees than ultrasonic. Similar limitations + wood decay type impacts detection: brown-rot fungi damage easier to detect than white-rot fungi damage. May not detect some types of decay.

Metriguard Model 239A $5,375. Metriguard, Pullman, WA
FAKOPP Microsecond Timer $1,970. FAKOPP Ent., Hungary
FAKOPP 2D Microsecond Timer 6,8,16-channel versions $4,820 - $11,390 FAKOPP Ent., Hungary
IML Impulse Hammer $2,000. IML, Germany

Microdrill wood decay detection

A small 2-3mm probe-drill up to 1m in length penetrates the wood using a constant, measured force. The force required for the drill to penetrate is measured and graphed. Information is limited to the area immediately surrounding the drill probe. Cannot detect early stages of wood decay.The drill opening may spread decay or invite new decay. Units with a flexible probe can present deflection errors. Longer probes add significant cost.

Consider using together with the Shigometer.

SIBTEC Digital microProbe
basic kit
+ Field Printer
Sibert Technology, England
IML Resistograph F-series
(300 - 500 mm)
w/electronic unit
$3,800 - $4,600.

IML, Germany

Note: USDA FPL Study [20]found
Drilling Resistance - Deterioration Index - Doug Fir

25 -100% - Sound Wood
10 - 25% - Moderate Decay
00 - 10% - Severe Decay

IML Resistograph - 2012 model  

Comment: Resitogrpah's new drill (the PD) is substantially different from the one used as the basis of the 2005 article referred to. That model was (apparently) based on an attachment fitted to a battery drill and drill penetration speed and rotation speed were linked mechanically. The new drill has independent computer control for penetration depth rate and rotational speed is set – not subject to how hard the operator squeezes the trigger. The embedded firmware is also programmable to detect cavities and other anomalies such as splits and checks AND ignore defects that the operator adjusts settings  for.

We have also developed a report template ( word with xl spreadsheet embedded ) and are using Dell tablets with WIN 7 so that results are wirelessly sent from the drill and the report  is prepared as investigation proceeds. Either we preload elevations for onsite mark-up of test areas or take a photo with the tablet and mark-up on the photo we embed in the report. - P.P.

Other Micro-drilling resistance tool suppliers  

Tree Solutions, Seattle, Washington

SIBTEC Scientific, DmP (Digital microProbe) (United Kingdom)

Resistograph™, Frank Rinn, Heidelberg, Germany.

Electrical Resistance wood decay detection

A 2.38mm dia. drilled hole receives an 8" - 12" long sensing probe. Decaying wood cells release metal ions that change wood resistivity. Detects decay immediately adjacent to the test hole. This method can detect early stages of decay not detected by micro-drilling. Variations in wood moisture (season for living trees, building conditions for timbers) affect individual readings - possibly compensated for by taking comparative readings at other locations in the same timber. Borings may invite or spread decay. Other less invasive wood resistivity measurement methods are available (Larsson et als).

Shigometer $1,700. Osmose Wood Preserving, Buffalo, NY
Vitalometer   France

Mechanical wood decay detection

A very sharp core cutting tool removes a wood sample then measured on a stiffness/breaking-strength scale. The result is compared with a data for wood species. (Not all species provided)
Data only pertains to area immediately adjacent to the test opening. Multiple borings may be needed. Studies found this tool provided a sensitive method for both white & brown rot fungal damage. Borings may invite or spread decay.

Fractometer I
Fractometer II
Fractometer Electric
IML Germany

Mechanical wood decay detection

A long thin probe is inserted into a pre-drilled hole in the wood / tree. The insertion process uses a self-firing spring-loaded punch to progress into the opening. The number of "punches" measures wood density and condition. Properly-sized drill hole is critical for accurate measurement. Data only pertains to area immediately adjacent to the test opening. Multiple borings may be needed. Borings may invite or spread decay.

Portable Compression Meter n/a N/A

Visual wood decay detection

Can include visual examination of wood taken by a core sampler.

Increment Borer $200. - $500. Several

Manual wood decay detection

Portable drill and long thin 9mm bit used by an expert can quickly detect decay by noting resistance to drilling, discoloration of wood in the drill bit flutes, even sense of smell. Multiple borings may be needed. Borings may invite or spread decay.

Plastic Mallet

Portable drill & common bit

$ 10.


Wood or Tree Test Instrument Manufacturer Contacts
Fujikura Europe http://www.fujikura.co.uk/
James Instruments http://www.ndtjames.com/ultrasonic.html
Fakopp Ent http://www.fakopp.com/main.htm
Sylvatest http://www.cbs-cbt.com/TECH/index_s_en.html
Metriguard http://www.metriguard.com/metprod.htm
IML http://www.imlusa.com/index.php
Sibert Technology http://www.sibtec.com/digitalmicroprobe.html
Osmose Wood Preserving http://www.osmose.com/utilities/products/accessories/

Adapted from Evaluation of Decay Detection Equipment in Standing Trees, Bob Monk, USDA Forest Service [16]

Mr. Monk's comments include the following qualifications about the equipment in this list:

More sophisticated devices such as X-ray, gamma ray tomography, magnetic resonance imaging, and thermal imaging are limited in use because of cost and practicality of field use. Some of these latter devices may have more practicality with evaluation of logs rather than standing trees.

There is a large amount of information available about individual pieces or types of equipment. There is also some information comparing some of the devices. Some information is in formal reports and some is more anecdotal, some is by the manufacturers of the equipment (need to be careful not to put too much weight on their claims). So far no report has been found that compares all of the equipment. Much of the work has been done in Europe (England and Germany mainly) and that is where much of the equipment is manufactured.


The original authors' article without the expanded discussion added here can be seen at An Introduction to Micro-Drilling Technology for N. Z. Structural Timber Assessment. [PDF]

Additional comments, illustrations, and technical citations addressing wood structure testing technologies have been added. We and the original authors invite and will reply to reader questions and comments using the comments box found at the end of this article. Initial technical review completed 8/6/201



Continue reading at WOOD BEAM VISUAL INSPECTIONor select a topic from the More Reading links shown below.

Or see STRUCTURAL DAMAGE PROBING - low-tech (ice pick or screwdriver probing) procedures used by building inspectors in the field


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