Dry Rot vs Wet Rot – Essential Differences for Property Owners
 

Understanding the difference between Dry Rot (Serpula lacrymans) and Wet Rot (Typically Coniophora puteana) is crucial when diagnosing timber decay in UK buildings. Each fungus behaves differently, spreads differently, and requires a different remediation approach.

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Dry Rot: The Most Destructive Timber Fungus in the UK

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Dry rot begins when timber becomes damp, but once active it can:

• Survive at relatively low moisture levels (20–30%)

• Spread through masonry using thick, grey “strands”

• Transport moisture as it grows

• Decay timber rapidly, leading to serious structural compromise
   

Key Identification Features:

• White/grey cotton-like mycelium

• Rust-red spore dust

• Strong mushroom odour

• Timber breaking into large rectangular “cuboidal” cracks
   

Because dry rot can travel through masonry, it often affects areas far beyond the original leak or damp source.
 

Wet Rot: Localised Timber Decay Caused by Continuous Moisture

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Wet rot occurs where timber has remained persistently wet—typically due to leaks, defective pointing, rising damp or poor ventilation.

Unlike dry rot, wet rot:

• Requires high moisture (40%+)

• Cannot travel through masonry

• Remains confined to the damp area

• Causes the timber to soften and darken rather than shrink and crack into cubes
   

Key Identification Features:

• Soft, crumbly or spongy wood

• Damp, earthy smell

• Localised damage rather than widespread spread

• Fibrous cracking rather than cuboidal cracking
   

Wet rot is less destructive but still a significant issue if affecting structural members like joists or lintels.

 

 

Image Credits: By Mätes II. - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3905756

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By Michel Langeveld - https://www.inaturalist.org/photos/107161014, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=97568122

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