NASCLA Accredited Commercial General ContractorWoodMedium
A contractor is evaluating the condition of existing wood framing in an older commercial building for a renovation project. Signs of powdery residue and small exit holes are observed in several floor joists. What is the most likely cause of this damage?
- APowderpost beetle infestation
- BDry rot fungus
- CTermite infestation
- DCarpenter ant activity
Show answer & explanationAnswer & explanation
Correct answer: A. Powderpost beetle infestation
Powderpost beetles are known for producing fine, flour-like powdery sawdust (frass) as they tunnel through wood, and their exit holes are typically small and round, about 1/16 to 1/8 inch in diameter. This description perfectly matches the scenario. Dry rot causes cracking and crumbling, termites leave mud tubes, and carpenter ants excavate tunnels but leave coarser sawdust.
Why the other options are wrong
- B. Dry rot causes wood to become dry and crumbly, often with deep cracks, but typically no powdery residue or distinct exit holes from insects.
- C. Termites consume wood internally and typically leave behind mud tubes and galleries, not fine powdery residue and small exit holes.
- D. Carpenter ants excavate galleries in wood, leaving behind coarser sawdust (frass) that often contains insect body parts, and their tunnels are smooth, not filled with fine powder.
Powderpost Beetle Damage
Damage to wood characterized by small, round exit holes and fine, powdery sawdust (frass) left by the larvae of powderpost beetles as they tunnel.
- Frass resembles talcum powder or flour.
- Exit holes are typically 1/16" to 1/8" in diameter.
- Infest hardwoods primarily, but some species attack softwoods.
Memory trick: Powderpost beetles leave dust like flour, and tiny holes that show their power.