A Brief Summary by S&A of:
APTI Article, Vol XXXVIII No. 2-3, 2007 Page 36, by Mr. Ronald W. Anthony.
3 Primary Reasons to Conduct a Wood Inspection
- Concerns about moisture and it’s effects.
- Deterioration, both physical and biological.
- Need to determine material properties.
Highly Variable Wood Behavior
- Different species.
- Rate of tree(Measured in Growth Rings per Inch).
- Age of tree.
- How the wood was cut from the log.
- Presence of defects.
- End use conditions.
Concerns About Moisture
- Paint peeling, stains, warping.
- Active leaks.
- Decay + insects associated with moisture.
- Moisture measurement.
Concerns About Deterioration (Weathing)
- Results of weathering, overload failure, mechanical failure, shrinkage.
- IMPORTANT: Checks can be o.k. Checks in structural members that “meet” are of concern.
- Differential shrinkage in mortise & tenon can lead to failure.
- Weathering of Wood: Cyclic wetting and drying, exposure to UV light & erosion by windblown debris.
Concerns About Deterioration (Biological)
- Fungal or insect attack.
- Bacteria degradation possible but not common in historic buildings because fungi + insects act more rapidly.
- During inspections – focus on fungus and insect activity.
- Be aware of moisture absporption through endgrain. Internal mositure retention causes decay, and not always visible.
- Inner growth rings better resist decay.
- Mildew: Grows on surface – does not damage wood.
- Stain Fungi: Propogates through wood but does not cause effect strength.
- Decay Fungi: (Alert Here) Breaks down wood composition. Types include: Brown Rot, White Rot, Dry Rot. It is important here to identify location and extent of rot.
- Incipient Decay: (Early stages of decay) Discoloration + initial loss of integrity of wood. Use an awl or screwdriver to discover soft or punky wood.
- Intermediate Decay: Small voids have developed.
- Advanced Decay: Tools to measure interior decay – Incriement borer, hand drill. More advanced technique – Resistance drilling, to determine extent of damage.
- Termites: Detection by presence of mud tubes.
- Wood Boring Beetles: Create holes packed with “frass.”
- Carpenter Ants + Bees: Leave large open holes.
- For both insect and damage and decay, effective cross section properties of the members can be determined and used for structural analysis.
- Determine wood species.
- Tools for Wood Inspection: 1. Visual inspection 2. Sharp probe 3. Moisture Meter 4. Telescoping mirror and flashlight.
- Visual ID’s: MIssing or broken pieces, fungal decay, moisture.
- Probe ID’s: Internal voids.
- Moisture meter: provides approximate values.
- Conductance meter (Resistance Moisture Meter): Used for heavy timbers. This method is useful for determining whether the wood is drying or taking up moisture.
Advanced Investigative Techniques
- Stress wave analysis: Location of advanced decay.
- Resistance drilling: Quantify loss of material.
- Digital Radioscopy: View hidden conditions.
Where to Look
- Wood in contact with the ground.
- Wood exhibiting moisture stains.
- Wood with visible decay.
- Roof penetrations.
- Attic sheathing, framing lumber and timbers.
- Sill beams and wall plates, particularly when in contact with masonry.
- Floor joists and girders, particularly where resting on exterior walls.
- Openings (doors and windows)
- Material interfaces.
- exterior woodwork.
- crawl space and basements.
- areas of structure that have been altered.