Timber pathology — understanding dry rot In timber used for construction, “dry rot” most characteristically causes which outcome over time if unchecked?

Introduction / Context:
Dry rot is a serious fungal decay of timber. Despite the name, it requires moisture to initiate, but it can continue at relatively low moisture levels once established. Recognizing its hallmark effects is essential for building maintenance and preservation.

Given Data / Assumptions:

• Timber has been exposed to damp conditions sufficient to start fungal growth.
• Poor ventilation and hidden leaks may be present.
• No remedial treatment has yet been applied.

Concept / Approach:
Dry rot fungi digest the cellulose and hemicellulose, leaving weakened, brittle wood. As decay progresses, the timber loses cohesion and can crumble or powder under light pressure. This represents a severe loss of cross-section and mechanical capacity.

Step-by-Step Solution:

Verification / Alternative check:
Laboratory identification of fungal species and moisture mapping confirm diagnosis; structural assessment quantifies residual capacity.

Why Other Options Are Wrong:

• Cracking only (A) and shrinkage only (D) ignore biochemical degradation.
• Minor strength reduction (B) understates the severity.
• Surface staining (E) may indicate mildew or superficial mold, not destructive dry rot.

Common Pitfalls:
Assuming “dry” rot occurs without moisture; failing to remove moisture sources; treating only the surface without replacing severely degraded members.

Final Answer: