Termites in sill plates (C) Daniel Friedman Structural Wood Damage Probing
Wood structural member assessment for rot, insect or fire damage

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Wood damage assessment in buildings:

This article describes methods for inspecting, probing, and otherwise assessing wood structures and wood components (floors, trim, sheathing) for damage by insects or rot.

We describe when, where, & how to inspect & probe wood components on buildings when damage (carpenter bees, carpenter ants, termites, powder post beetles, fungal damage, rot damage) is seen, known, or suspected.

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How to assess the extent of structural damage from wood destroying insects

Collapsing barn (C) Daniel Friedman powder post beetle damage (C) Daniel Friedman

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Article Contents

Assessing the extent of structural damage to wood framing members in a conventional building inspection involves the following phases and procedures:

Visual inspection to locate evidence of insect damage or structural rot

Watch out: Don't assume only one kind of insect damage will be present as the same conditions that invite one insect into a wood structure may invite others. We have found termite damage, carpenter ant activity, and powder post beetle damage all in the same structure, on occasion even in the same wood beam or joist.

Our photo (above right) illustrates wood rot found in the same floor joist where there was extensive termite damage.

Selection & use of probing tools to test wood components for insect damage or rot

Using an appropriately-chosen instrument (see below) probe suspect or visibly damaged wood beams, joists, rim joists, sill plates, even flooring or subflooring; we start this step in basements and crawl spaces but may find evidence to justify probing finished materials such as interior trim or wood floors.

Wood probe using screwdriver (C) Daniel Friedman powder post beetle damage (C) Daniel Friedman

Professionals use a wide variety of wood probing instruments of different end-diameters, sharpness, and, importantly, length, as it can be difficult to reach some surfaces that really should be examined. Our photo (above left) illustrates using a simple screwdriver, (my dad's), to probe an area of visible termite damage. And at above right, our pen is probing suspected rot damage at wood siding.

An example of probing a finished hardwood floor is at TERMITE INSPECTION & DAMAGE.

Watch out: building inspectors and PCOs should never probe nor use destructive inspection methods without permission of the building owner. Make certain that you have explained the justification for any inspection techniques that involve risk of damage, even just cosmetic damage to the structure. However, in our OPINION, if your finger or pen easily penetrate insect or rot damaged trim, flooring, or other indoor finished surfaces, you have not caused actional damage to that component; rather, you have disclosed it.

We arbitrated an ugly case in which a novice home inspector left screwdriver blade jam marks throughout the finished area of a new home. Don't do that.

The depth to which a wood probing instrument will penetrate wood depends on these factors

Micro Drilling in-situ timber test - Incodo, Tauranga New Zealand powder post beetle damage (C) Daniel Friedman
  • The hardness of the wood being tested. At above left our photo illustrates micro-drilling (explained at WOOD STRUCTURE ASSESSMENT), courtesy of Paul Probett, Incodo Forensic Building Specialists [1].

    At above right you can see the butt end of our screwdriver, buried to the hilt in a termite-damaged sill plate located at the base of an interior partition in the basement of a New York home. The screwdriver penetrated this sill with virtually no effort. Probett calls this traditional wood inspection and probing method "Visual and Chisel" (WOOD BEAM VISUAL INSPECTION) - an approach that in our opinion is perfectly adequate in many circumstances.
Termites in sill plates (C) Daniel Friedman
  • The condition of the wood: water content, and most significantly the extent and depth of insect damage (or rot) nto the wood. This step is key in assessing powder post beetle damage as it is difficult to know before probing whether the damage is superficial ("topical") or much more extensive.

    Our screwdriver penetrating the floor joist (photo at left) confirmed extensive termite damage in this joist that formed the ceiling over a basement utility room whose partition wall sills were also termite infested (photo above right). Finding damage in both floors and ceilings of this home continued the trail of disclosure of a very extensively damaged structure.

    Many inspectors and some engineers use rules of thumb about probe entry depth to form an opinion about the remaining strength of the structural member and whether or not it needs replacement.
  • The cross section and area of the tip of the probe. Using a sharp pointed ice pick to probe wood is ridiculous as the pointed tip will penetrate just about any wood and will make unnecessary holes and damage.

    Our fine wood probe (shown at below left) was made by grinding off the sharp point of the ice pick to a flat end. We use this probe delicately and in discrete locations such as at the bottom of wood trim in unobtrusive areas of suspected damage.
  • The force applied to the wood test probe. Except for the use of instrumented microdrillingv this step involves some subjectivity and is based on the experience and knowledge of the inspector.
  • See TIMBER ASSESSMENT for details about microdrilling, an engineering approach to assessing the strength of damage-suspect structural wood.

Examples of probing wood for structural damage

Clearly the ground-off ice pick wood probe (below right) is finding less-severe damage than the "to the hilt" stab of my dad's screwdriver demonstrated by our client (below left).

powder post beetle damage (C) Daniel Friedman Powder post beetle old house borere damage photographs (C) D Friedman D Grudzinski

Watch out: while we advise against unwarranted cosmetic damage at a building interior, strategic probing of wood sills, rim joists, or floor structures (or other wood members) can disclose severe structural damage that was otherwise not evident. At below left, even our pen was able to easily puncture this termite-damaged joist that had been "cosmetically-repaired" using wood putty

At below left we illustrate an appropriate use of our fine wood damage probe in an area of suspected cover-up of a termite damaged oak floor framed at ground level with no other access below.

When observing the termite damage at below right, probing adjacent wood members as well as along the length of the visibly attacked members is completely appropriate. This termite damaged floor that was "repaired" with wood putty is described in detail at TERMITE DAMAGE PROBING.

Termite damage case (C) Daniel Friedman Photograph of  termite damage to the floor structure of a 1920's home.

And at below left our termite damage photograph illustrates a serious risk: this floor joist looked "perfect" from its exterior, but probing disclosed that it was severely damaged - basically a "hollow skin" of wood. The light colored marks at the upper edge of the joist (and suspected termite activity from other site clues) led us to probe this joist bottom where it rested on the sill plate. Leverng the screwdriver disclosed the damage our photo illustrates.

Photograph of  termite damage to the floor structure of a 1920's home. Carpenter Ant Damage (C) Daniel Friedman

At above right,my pen, with its cap on, easily penetrated this severly-rotted joist end.

Demolition or removal of materials for further inspection for WDI damage: when is it justified?

Demolition or removal of materials for further inspection for insect damage may be justified and necessary. Usually powder post beetles have attacked wood beams, typically rough cut lumber or round "trees" used as joists or beams or sills in older homes. We don't usually need to remove flooring or siding to access and assess such damage, but there are cases where it may be needed.

  • Inaccessible crawl areas: In some cases such as where there is an inaccessible crawl space we may need to make inspection or access openings to the crawl area, either from outside the building or even from indoors.
  • Buckled, crushed building siding: siding buckled at ground level over an inaccessible crawl space or slab on grade (photo, below left) is a likely indicator of severe hidden rot or insect damage to the building's sills and floor structure. Further inspection from outside is usually justified. Even siding buckled atop a foundation wall above ground may indicate a risk of crushing sills that merits further investigation such as our cement asbestos siding photo (below right).
Buckled siding at ground level indicates sill crushing (C) Daniel Friedman Photograph of - damaged vinyl siding
  • Additional materials removal during building repairs can also be expected to disclose damage from insects, rot, or mold. In general we remove damaged materials until there is a suitable safe margin of clean un-damaged materials, extending that distance of removal of wood framing where necessary for structural reasons (replacement of an entire member for practical or cost reasons) or in special cases such as MERULIPORIA FUNGUS DAMAGE (photos shown just below) we remove wood for a larger safety margin, as much as two meters beyond visible damage due to hidden fungal infections.

Poria house eating fungus Meruliporia poria house eating fungus

Also see the FEAR-O-METER a promotion theory to convert risk of hidden defects & hazards into action thresholds, for a discussion of how an accumulation of inspection evidence leads to a rational decision to perform invasive or desctructive inspection measures.


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