Collapsing building © Daniel FriedmanVisual Inspection Methods for Structural Wood Timber or Beam Damage Assessment
How experts assess the structural integrity of wood framing or wood timbers in-situ

  • WOOD BEAM VISUAL INSPECTION - CONTENTS: assessment of the effectiveness of visual assessment of the condition of wood beams & timbers or wood framing to detect wood rot & structural damage
  • 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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Using visual inspection methods for determining the soundness of wood structural members:

Here we describe a visual approach to inspecting the condition of wood structural members: beams, timbers, studs, joists, rafters in buildings & other structures. The authors describe the limitations of visual inspection, and in other sections of this article series they evaluate other approaches to evaluating wood structures for damage.

This article series describes the various 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.

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Visual Inspection Methods for Wood Structural Member Assessment

Micro Drilling in-situ timber test - Incodo, Tauranga New Zealand

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.

[Click to enlarge any image or illustration]

Expert eye (“visual n chisel”) Inspection for Wood Structure Damage

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. Details are

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:

Timber frame rot (C) Daniel Friedman
  • 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 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.

    Note [DF opinion]: wood sample coring or micro-drilling technology has evolved from methods used by arborists to assess the condition of standing timber - trees. If you have observed the rotted or insect-damaged hollow core of a cut or fallen tree you will understand the more extreme damaged condition being sought by the arborist in evaluating standing timbers. In contrast, the rot damage found on timbers and beams used in buildings usually develops from the outside-in as water leaking into a structure is more likely to first wet the exterior surface of a structural member than its interior. For this reason, surface inspection and manual probing can be useful and, with thought, reliable.

    Watch out: however not all structural beam and timber damage occurs from the outside in. As we demonstrate
    at STRUCTURAL DAMAGE PROBING, wood destroying insects often attack the interior of a wood structural member and particularly in the case of termite damage, may leave the beam or timber exterior surface looking intact.
  • 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.



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 added these comments.

Also see ADVANCED INSPECTION METHODS "Developing your X-Ray Vision" - DF

Rotting timber frame sketch (C) Journal of Light Construction, Steven Bliss

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.

At STRUCTURAL DAMAGE PROBING we demonstrate successful use of manual probing combined with visual inspection to find and assess rot and insect damage in visually accessible wood framing members. - 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 series , 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.

V4a 06/12 - ####

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



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