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 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.

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

Paul 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. 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

[Click to enlarge any image or illustration]

Article contents

• WOOD STRUCTURE ASSESSMENT - 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.
  
  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. we describe the relationship between construction details and the occurrence of structural rot in timber frame buildings.
  
  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 Compared with Other Current Bases for Wood Structural Member Assessment.
  • TABLE of TREE DECAY DETECTION EQUIPMENT
  • WOOD BEAM VISUAL INSPECTION - Visual Inspection Methods for Wood Structural Member Assessment
  • WOOD BEAM MICROBIOLOGICAL ASSESSMENT - Microbiologist / Mycologist Methods for Wood Structural Member Assessment
  • WOOD BEAM FRACTOMETER TESTING - Fractometer Methods for Wood Structural Member Assessment
  • WOOD BEAM PILODYN TESTING - Pilodyn Methods for Wood Structural Member Assessment
  • WOOD BEAM MICRO-DRILLING ASSESSMENT - Micro-Drilling: Resistance drill Methods for Wood Structural Member Assessment. Incodo Testing Program of Micro-Drilling for Wood Assessment
  • WOOD BEAM MICRO-DRILLING PROCEDURES - details of how micro drilling is used to assess wood structural member condition
  • WOOD BEAM MICRO-DRILLING EFFECTIVENESS - Incodo study of microdrilling for wood structure assessment
  • WOOD BEAM ROT ASSESS: MOISTURE METERS - are moisture meters useful for rot detection in structural members?
  • WOOD BEAM ROT ASSESS: THERMOGRAPHY - are infra red IR scanners and thermography equipment effective in detecting structural rot in wood beams?

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]

The 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.

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

• 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.

Similarly

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:

• WOOD BEAM VISUAL INSPECTION
• WOOD BEAM MICROBIOLOGICAL ASSESSMENT
• WOOD BEAM FRACTOMETER TESTING
• WOOD BEAM PILODYN TESTING
• WOOD BEAM MICRO-DRILLING ASSESSMENT
• WOOD BEAM ROT ASSESS: MOISTURE METERS
• WOOD BEAM ROT ASSESS: THERMOGRAPHY

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.

Visual Inspection Methods for Wood Structural Member Assessment

Expert eye (“visual n chisel”).

We contend that this approach is subjective and has issues regarding cost, independence between the assessor and the remediator, liberal vs. conservative "safe" approaches to deciding what replacement is needed, and that in some cases visual inspections lack adequate evidential basis for decisions.

Nevertheless, 99% of building assessments use this approach.

The scope of visual-based wood structure inspections focuses on the visible surface of materials.

Additional properties of the visual & chisel approach to building structural damage assessment:

• Highly subjective – based on experience and opinion – some “brashness” /chisel testing of suspect areas. Often supported by microbiological testing which adds to net cost


• Often linked with conservative approach
  
   to extent of removal - the expert plays it safe, avoiding personal liability by spending more of the client (or government's) money
• Relatively expensive and report quality ( if prepared) varies

• Some inspection reports are not objective 
  
  scientific or to an evidential level.
• Other inspection reports rely only on lab tests
  
   but offer no or insufficient actual onsite inspection and no or insufficient interpretation of the lab test report results.
  
  Watch out: we [DF] receive frequent consumer complaints from people who hired an "expert" to inspect their home for hidden damage only to find that the expert did little other than collect a test sample, without any actual building inspection.
  
  The test sample is "tossed over the wall" to a forensic test laboratory who in turn issue a report based solely on the sample contents. The "expert" defers to the lab report and offers no useful interpretation of the test report.
  
  The lab cannot adequately interpret the significance of the test sample finding because no one there has examined the structure concerned nor interviewed its occupants.
• May miss hidden decay if the expert is not adequately trained & experienced
• High likelihood of missing timber degraded to non- compliant levels particularly between double studs and joists or at similar potential problem spots that are not visually accessible and for which there is not yet any external building evidence such as sagging, cracking, movement. The risk of this error is increased if the inspector does not attend to secondary clues such as stains, building leak history, construction details that are prone to developing leaks, rot, insect damage.
• Some defects or the extent of building damage cannot be effectively assessed until cladding or linings have been removed

Watch out:  a building inspection to assess the risk of hidden damage to its wood structure, when performed by an experienced professional will consider the entire structure based on a thorough outside as well as inside inspection.

The inspector recognizes building methods, materials, or site conditions that tend to cause moisture, leaks, or rot problems as well as recognizing visually obvious examples of such damage.

Where the site conditions and history justify further, more invasive inspection (such as making test cuts to explore the most-suspect areas) the inspector is expected to so indicate. Such an inspection balances the risk of hidden damage against the costs of unnecessary or unjustified destructive or invasive inspection methods.

See TIMBER FRAMING, ROT and

also MOISTURE CONTROL in BUILDINGS - DF

Note: I [DF] agree that the actual visual inspection of building conditions, lacking "X-ray vision", is limited to external or surface observations. However a skilled and experienced observer can predict areas where hidden damage is most likely at a particular building by considering building and site history, construction materials, construction methods, and by familiarity with construction details that tend to lead to building leaks, moisture problems, rot, damage.

Therefore I have addia.com/home_inspection/Building_Inspection_Techniques.php">ADVANCED INSPECTION METHODS "Developing your X-Ray Vision" - DF

This sketch, courtesy of Steven Bliss & The Journal of Light Construction, illustrates the problem of structural decay that may be completely hidden as well as "dry" at the time of a building inspection.

At TIMBER FRAMING, ROT we discuss this problem in detail, and at

ADVANCED INSPECTION METHODS we emphasize the importance of thorough, experienced, attentive inspection to not just evidence of damage, but evidence of construction materials and methods that tend to cause damage - the risk points at a building. - DF

More-expert inspectors make limited use of instruments such as moisture meters, infra-red scanners & thermography, and more significantly, by familiarity with construction methods and materials, building science, and building failures, an expert inspector can focus attention on areas where hidden damage is most likely to occur.

But as we and the USDA FPL warned at the start of this article, an expert who approaches building assessment most effectively does not allow the use of an instrument to substitute for a thorough visual inspection and site history recording.

Microbiologist / Mycologist Methods for Wood Structural Member Assessment

Expert, samples, time, cost. Often additional to visual assessment

Scope = Microscopic to sample size (minor usage in deciding actual replacement, adds genuine weight to reports). Not in situ assessment

Note: in our opinion, microbiologists and aerobiologists can provide a useful supporting role in assessing building conditions (mold or other IAQ hazards) including providing additional screening for evidence of hidden but active wood destroying fungi.

Few microbiologists nor mycologists have the requisite familiarity with building science and construction failures to serve as a primary building screener for hidden damage.

But those sciences can add important depth of understanding to field observations by others. For example, a mycologist can explain that if we see "mushrooms" growing out of wood framing members, there is almost certainly substantial hidden rot damage that merits further invasive inspection.

Similarly, the identification of some mold genera/species by spore trap or dust sampling can yield important insights into building conditions and the risk of hidden damage.

For example we have found high levels of Meruliporia incrassata. spores in building environmental samples at levels indicating a nearby infection of this wood destroying fungus. But unless the work is conducted by someone who is also expert in building science and who is also familiar with construction methods and construction inspection methods, such assessments are likely to be unreliable.

See Meruliporia Mold Photographs for details. Photo, above left of Meruliporia incrassata and other fungal materials - Daniel Friedman, InspectAPedia lab.

Watch out: In our view, building "testing" by collecting surface, air, or dust samples for lab analysis, while they can considerably expand the scope of a building assessment beyond "microscopic sample size", are of questionable accuracy unless there is accompanying expert visual inspection and history taking.. - DF

Fractometer Methods for Wood Structural Member Assessment

5mm cores required – compression, bending and torsional tests.

Scope = Specific samples only, but comprehensive. Not in situ assessment.

With the use of the increment borer one can take a core sample out of a wooden structure with a diameter of 5 mm. This core sample is then used for assessing with the Fractometer Print.

A Fractometer Print puts bending load on the core sample that was taken from a wooden structure until it breaks.

The bending break moment and the breaking angle can be determined as can compression strength and other measures.

The Fractometer has been described in IML's instruction manual where bending strength, fiber direction, and related concepts are detailed. - IML is Instrumenta Mechanik Labor System, Wiesloch, Germany. [15] .

Pilodyn Methods for Wood Structural Member Assessment

Instant, cost effective.

Scope = 40mm (density loss measurement). Generally not used on buildings. Largely utility poles only for shell decay testing.

According to Pilodyn and corvib.com, the Pilodyn is suitable for trees, railway ties and utility poles. According to Ferret (AU), the Pilodyn is also suitable for testing the stability of wooden structures on playgrounds, detection of soft rot.

Pilodyn illustrations from Corvib.com. [17]

 

 

 

• Pilodyn Advantages / Disadvantages:
  • 40 mm penetration maximum
  • Spring loaded penetrometer
  • Sound timber equates to only 15-25 mm penetration
  • Analogue scale
  • Cost about $1000 - 2000. NZ per assessment
  • Disposables cheap – pins only
  • Hidden decay difficult to identify
  • Extremely robust
  • The Pilodyn wood tester (Hylec Controls) is described by and currently available from InTech/NDE U.S. Tel: 905-716-5604 / 800-297-3208, or Email: bnadeau@intechnde.com, and is also available from Hylec Controls via Ferret.com in Australia. - DF [17][18][19]

Micro-Drilling: Resistance drill Methods for Wood Structural Member Assessment

• Capital and start-up cost high, evidential, and instant.
• Scope = Full depth of sample, instant strength loss measurement
• Microdrill equipment is provided by
  • Siebert Technology, England: SIBTEC Digital microProbe
  • IML, Germany: IML Resistograph
• Details are provided in this article just below.

Image of micro-drilling, USDA FPL [20] .

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

Notes to the table above

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). S

o 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.

Moisture Meters Useful in Spotting Areas of Extra Risk of Structural Rot Damage

Our preferred moisture meter is a Trotec T2000  http://www.trotec.de/en/product-catalog/measuring-instruments/multi-function/t2000/.

This tool accepts a wide range of input sensors including 16+ variations on pin type electrodes for measuring moisture in wood. Quoting from the manufacturer:

Multifunctional measuring instruments with digital precision without the measured value drift disadvantage of analogue instruments.

SDI input for serial sensors such as temperature, relative humidity, flow speed and destruction-free humidity measurement. In addition to the Trotec sensors you can not only connect electrodes from other manufacturers to the device with adapter cables but [the tool] will also be able to combine future sensor developments with the T2000. [24]

We find the “lollipop”  dielectric head particularly useful and the microwave head is of some use.

The unit also comes with a temp/humidity probe that is only 4 mm diameter and we use it on cavities and to determine moisture in concrete.

Interestingly the Trotec Manual also includes research from Aachen Univ that allows resistance readings in concrete and other non wood materials to be converted to MC%. - P.D.

For a study testing the effectiveness of several types of moisture meters for finding wet materials or surfaces hidden in wall cavities of a building with known current, recent, and previous leaks see MOISTURE METER STUDY .

We tried pin type and electronic moisture encounter meters as well as more invasive methods such as test cuts in suspect areas, followed by a complete interior surface demolition to disclose actual leak areas, both recent and historic.

Our photo (above left) illustrates the chance involved in using even a long-pin Delmhorst moisture meter to detect an exterior wall water leak that sent water running inside the wall cavity but down the side of the stud.

None of the moisture meters we tested could find this leak until we cut open the wall.

In general, pin type moisture meters work well at producing moisture content profiles in materials that have been directly wet or dampened such as wood or drywall that are directly accessible.

Probing deep inside wall cavities, as our photo above illustrates, is a hit-or miss proposition. Electronic moisture encounters work well at producing moisture content profiles on all surfaces and can detect moisture behind a ceramic tile wall. But these devices can be fooled by foil faced insulation, expanded metal lath, piping and wiring.

Also see MOISTURE CONTROL in BUILDINGS - DF.

Are Thermal Images Reliable for Spotting Areas of Extra Risk of Structural Rot Damage or Hidden Mold in Buildings?

OPINION: DF: Thermal images and IR have been widely used with some success at spotting areas of heat loss in buildings and these tools have a longer history of use in examining overheated electrical connections, motors, etc. But for finding hidden mold, thermography is a risky proposition.

Image at left, courtesy Paul Probett, Incodo [1]

Watch out: in the hands of the un-trained or unscrupulous these and other tools can wreak havoc or harm to consumers. The most egregious instrument snafu I've come across [DF] recently was a Hudson Valley New York "mold remediator" uses an IR camera to tell his clients where the hidden mold is located in their home - it was a modern version of the guy with the light meter who sold people replacement windows by showing clients where their heat loss was occurring - wherever there was light.

I did find areas of basement water entry and moldy insulation - in an area not addressed by the New York mold-thermographer.

Details about using thermal imaging to look for hidden mold are

at THERMAL IMAGING MOLD SCANS .

Also see FIBERGLASS INSULATION MOLD

Paul Probett adds: We had major problems with people buying thermal imagers, using ex military units and making ridiculous claims.

In 2008 I gave a power-point presentation [25] to a conference explaining how IR results can be fudged and I described the limitations of thermal imagers. 

(Our staff had been through the Infraspection Institute USA on-line course to level 2 the year before).

 

Visual Inspection Compared with Micro-drilling for Wood Structure Assessment

Article Contents:

• WOOD BEAM MICRO-DRILLING ASSESSMENT - Micro-Drilling: Resistance drill Methods for Wood Structural Member Assessment. Incodo Testing Program of Micro-Drilling for Wood Assessment
• WOOD BEAM MICRO-DRILLING PROCEDURES - details of how micro drilling is used to assess wood structural member condition
• WOOD BEAM MICRO-DRILLING EFFECTIVENES S - Incodo study of microdrilling for wood structure assessment

Micro-drilling measures drill resistance which is related to timber density and strength.

Visual /brashness testing supported with limited microbiological testing focuses on removal of all decayed timber as the critical element in decisions.

It is suggested that – as decayed frame replacement work is work undertaken under a building consent – testing or assessment should be based on compliance documents as far as possible.

This may involve a modification of current approaches to remediation practice by reference to existing building code documents as the preferred evaluation criteria for making timber retain or re frame type decisions.

How does Micro Drilling Timber Assessment Work?

Testing involves drilling a 2 mm hole in timber members up to 300mm

The drill is computer controlled with drill bit rotation rpms and linear penetration independent of each other and at pre-set levels applicable to the timber specie. This is a change from older generation microdrills that had rpm and penetration linked and power applied controlled by the operator.

Results are readable in real time via the onboard display as the graph is formed.

Typical testing for 100 mm p.rad framing is about 15 seconds.

Results are also processed according to developed timber specie parameters and appropriate standards (where applicable) so onboard software instantly gives a preliminary pass, fail or retest assessment of timber. Settings are adjustable to assist with the identifying of quality infractions, decay areas and splits or checks.

Information is then bluetoothed to a draft report and presented in a similar format to the following graphs and charts.

As highlighted in the 2010 RILEM State of the Art Report – In Situ Assessment of Structural Timber by Kasal and Tannert “ If strength values are require(d) the best drills available on the market are required as well as a high level of education and experience. This, proper education of the user is a critical point before applying resistance drilling” quote

Incodo endorse the above and suggest general usage, adjusting programmable settings interpretation and moderation of results is critical.

Micro-drilling In Situ Timber assessment

Test Results: Summary

• Base of studs where decay transmitted from wet bottom plate – timber frequently found to be sound within 150 - 200 mm possibly allowing splinting of studs rather than full replacement
• Double timbers joists and studs – frequently decay between members but sound outer faces.
• Some surface decay has limited penetration
• External corner studs behind direct fix cladding can have stepped clamping point decay

Test Results: Evaluation and Moderation

Test results indicate appreciable differences between sound and unsound timber. Noticeable anomalies on graphs indicative of issues include:

1. Partial or Full loss of all or some latewood peaks.
2. Smoothing of graphs along upper amplitude line affecting normal early wood and latewood norms (lower height of “saw teeth”).
3. Significant variation across a graph in different area.
4. General lowering of results in areas on same graph.
5. Sloping shoulders as graph drops to plateau or valley.
6. Sloping shoulder to graph at entry and exit points rather than near vertical step within 2-3mm of surfaces.
7. Acceptable anomalies which are readily identifiable include changes induced by splits, checks, knots, junction between two timber members and pithy cores.

While software is set to handle many of these factors, moderation of individual graphs is part of the testing process and recommendations are that all reports are moderated before being provided.

Test Protocols

Recommended testing involves checking bottom plates at 1.0m centres and as close as practicable to external corners. In addition testing focuses on high risk details such as window sill corners and points below, balcony to wall connections, base of apron flashings etc and wherever staining or other concern aspects are noted.

Inspection locations are plotted on a WIN 7 tablet using preloaded plans or elevations or on photos taken using the tablet’s main camera. Incodo have developed a suitable template for wirelessly transmitting data from the drill into an open report which can be prepared on the tablet or sent to the office for moderation and review.

Reports are comprehensive and targeted completion for reports is the same or following day after inspection.

Micro-drilling methodology testing for NZ timbers- A Basis

INCODO has undertaken substantial in-house testing to determine suitability of micro-drilling for assessment of low density plantation grown pinus radiata in particular.

Graph highlighting close correlations between X-ray density and resistance drill readings taken using a Resistograph micro-drill.

Quoting:

Profiles of radial X-ray density and drill resistance of the same larch sample.

Rilem - State of the Art Report In Situ Assessment of Structural Timber, Bohumil Kasal & Thomas Tannert, Springer 2010. [3][4][5][6]

 

In addition reliance has been based on studies by others* involving micro-drilling in Europe, USA and Australia related to structural timber in buildings and bridges.

The technology has been used for many years. The big difference is that the PD model is a new generation micro-drill with onboard firmware

*Ref www.printfu.org search “Resistograph” or “Sibtec”

Quote

“Wood density is the property which will be used as an example because of its’ close correlation with timber strength (Dadswell and Nicholls, 1959, Elliot 1970) …and because it is widely held by wood technologists to be the single most important wood variable (de Zeeuw 1965) According to Panshin et al (1963) the relationship between wood density and timber strength is expressed by

S = K (D)n

Where S is any of the strength properties, K is a constant, D is density and n is an exponent which depends on the strength property being considered”

- WOOD DENSITY OF RADIATA PINE: ITS VARIATION AND MANIPULATION – D J Cown, FRI

Incodo Testing Program of Micro-Drilling for Wood Assessment

Phase 1: Initial set up (completed)

Determining consistency of results using sound timber and establishing preliminary variable settings for software to determine Pass/Warning/Fail, Quality Infraction levels and identification of decay type voids.

Phase 2: Site testing and integration into report template (completed)

Initial site testing on buildings with wall framing exposed as part of remediation or demolition works. Three buildings – all in Auckland
Adjustment of settings for onboard software.

Build larger database of sound timber graphic levels to use as controls / base levels.

Phase 3: Outside consultant and further field testing (completed but ongoing consultation)

Consult ex FRI staff and engineers as to draft reports and use of terms.
Further testing on variety of common (and uncommon timbers incl. Matai, Pinus Syl. (Aus plantation), Pinus Rad. poles, Jarrah utility poles etc.

Determine further testing requirements.

Phase 4: Effect of moisture on consistency and reliability of test results (Completed – report at draft stage as at 05/12)

Assessment of impact of varied moisture levels on microdrilling results.

Undertake in-house testing using resistance moisture meter, H3.1 framing (to ensure no internal decay to skew results), Contherm drying oven, etc. Limited to 4 samples dried from 88-100%+MC to 12-14% Results (currently being tabulated)

Preliminary indications are that moisture level effects are limited and do not impact on micro-drilling assessments sufficiently to be of concern. (likely reason is considered to be that drill readings are a resistance reading and this is a combination reading of lateral penetrative resistance as well as shear loads required by the bit tip to slice through timber fibres at various angles to fibre orientation eg shearing occurs parallel and at random angles to timber fibre direction )

 

Sample 2 graph at left, at 88.0% Moisture Content (MC) indicated

 

 

and next graph (below) at indicated 14.4%MC.

 

Readings taken from new SG8 pinus radiata using Protimeter resistance meter.

Readings taken from points at 20mm centres, along plane of timber grain to ensure minimal impact to test in regard to variance of earlywood and latewood.

Net result indicates minimal graphical difference values between high and EMC (equilibrium moisture content) approximated moisture levels.

Phase 5: Fractometer comparison with micro-drilling including relationship to compliance documents. (Equipment sourced)

Comparison between test results and timber testing properties in accord with NZS: 3622:2004.

Further testing involving taking samples from critical points in sample(s) identified by test graphs, where there is a transition from sound to decayed wood and determining the degree of correlation to timber strength when tested for compression, bending and tension using an IML Fractometer Mark

Programmed testing also involves the same methodology being applied to other timber species as samples become available and demand and demand for micro-drilling testing is required.

Specific testing involves has involved sourcing dendochronological level dry wood core drills capable of extracting parallel to grain cores to test bending stiffness.

Phase 6: Microbiological comparison with micro-drill test results in timber transitioning from sound to decayed. (Possible test methodology)

Microbiological comparison of samples and phase 5 results by independent laboratory such as Biodet.

NOTE: The value of this testing is being considered and is not currently scheduled.

Arguably the decision to retain or replace building elements in leaky homes should be driven by timber meeting or failing the requirements of NZS:3602, :3603, :3604 and :3622. These are “strength” related criteria – not decay presence criteria.

As micro-drilling is considered to evaluate strength – it becomes a moot point whether decay impact is a Building Consent / Safe & Sanitary criteria that warrants consideration.

[Click to enlarge any image]

Argument in simple terms is - if the timber meets Building Code requirements, that is all that is required to meet for compliance.

This is the same for supplied timber for remediation which is tested for strength only.

Presence of incipient, surface or minor decay is irrelevant to decisions to retain or replace as effective remediation practice should ensure future moisture levels remain at or below 18% at which level any remaining timber decay fungi reportedly cannot thrive.

Current best practice remediation also includes in situ preservative treatment and removal of decayed timber which severely limits opportunities for framing to become structurally non-compliant at a later date. (If this was not the case complete exterior frame replacement should be the norm)

Phase 7: Blind test of hidden framing (Possible Test)

Assess building ready for extensive remediation and reclad using NDT moisture meter to help determine focus points from inside only and using micro-drill to test largely through external wall skirtings and or window liners etc

Note drill used in concert with metal detector/ stud finder for safety etc

Compare report(s) with actuals after cladding removed

Watch out: for moisture meter limitations: we [DF] have tested and demonstrated that while moisture meters are an invaluable tool in assessing building conditions, none of the moisture meter designs presently on the market can reliably detect all wet or leak in conditions in all sorts of building structures and cavities.

• Moisture meters only detect current or recent leaks or moisture traps that have not dried out; past leaks and concomitant rot or insect damage in areas now dry will not be detected by a moisture meter
• Moisture meters vary in the depth to which they can sense water or moisture in a structure, depending on sensing pin length, depth to which pins are inserted into a material, or depending on the circuit design of electronic moisture meters.
  
  A short pin moisture meter will not reliably detect moisture deeper in the wall cavity such as in the wall insulation or on the cavity side of exterior wall sheathing. Even a long pin moisture meter, probing through drywall and into wall or ceiling cavity insulation, may not detect water on the surface of exterior sheathing nor even soaking wet water rivulets running down a portion of the side of a vertical stud or timber.
  
  It's "hit or miss" using a moisture meter as a leak screening device without the accompaniment of an expert visual inspection.
  
  Details are at MOISTURE METER STUDY . - DF

Note: Above information is copyright, commercially sensitive and is yet to be peer reviewed. It is not to be copied or circulated without the express and written permission of Incodo Limited. Adapted here by InspectaPedia.com, with permission from Incodo 8/5/2012, technical review is in process.

V4a 06/12 - ####

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Continue reading at WOOD STRUCTURE ASSESSMENT or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX .

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