What is the Difference Between Wet Rot and Dry Rot

The key difference between wet rot and dry rot is that wet rot is a fungal decay that requires a higher moisture content to grow, while dry rot is fungal decay that does not require a higher moisture content to grow.

Wet rot and dry rot are two common forms of fungal decay found in timbers. These fungal decays tend to affect the quality of timber. Both forms of fungal decays are caused by fungal spores already present in the timber. These fungal spores grow and spread when enough moisture is present in the area. Since both forms of fungal decays cause significant structural issues in timbers, they should not be left untreated. Hence, it is very important to identify them correctly in advance.

CONTENTS

1. Overview and Key Difference
2. What is Wet Rot 
3. What is Dry Rot
4. Similarities – Wet Rot and Dry Rot
5. Wet Rot vs Dry Rot in Tabular Form
6. Summary

What is Wet Rot?

Wet rot is one of the two forms of fungal decays found in timber. Wet rot requires a high moisture content to grow. The causative agent of wet rot is the fungal spores of Coniophora puteana. The growth of wet rot requires higher moisture content than dry rot in timber. The wet rot will begin to grow in the timber or other permeable surface when the moisture content reaches around 50%. Normally, this high moisture content comes from an external leak or water ingress from guttering, plumbing, and stone pointing.

Soon after the identification of wet rot, any water leak should be repaired to prevent recurrence before treating the wet rot condition. Once the high moisture content is removed, the wet rot stops growing. In addition, it’s necessary to replace the timber in the affected area to control wet rot. The common signs of wet rot are damp, musty smell, softened timber, cracking timber, discoloured timber, weakened timber or black-brown fungal growths.

What is Dry Rot?

Dry rot is the second common form of fungal decay found in timber. Dry rot does not require a higher moisture content to grow in comparison to wet rot. Dry rot is due to the fungal spores of Serpula lacrymans. Dry rot requires only 20% moisture content in the timber to begin growth. However, dry rot will not grow in dry conditions. Often, homes with high humidity and poor ventilation are susceptible to dry rot. One early warning sign for dry rot is condensations on windows. If people live in a wet or humid area, they should take care to ventilate their homes properly. This will prevent moisture build-ups.

It is important to identify and remove the source of moisture before treating the specific fungus. Usually, dry rot is found in hidden areas such as floorboards or behind walls. Dry rot should be identified very early; otherwise, it can cause severe damage to timber and spread to other regions of the home. Moreover, fungicides can control dry rot. The common signs of dry rot are damaged timber, damp, musty smell, deep cracks in the timber, brittle timber, orange-brown spore dust, grey strands on timber or fruiting bodies like mushrooms in the timber.

What are the Similarities Between Wet Rot and Dry Rot?

• Wet rot and dry rot are common forms of fungal decay found in timbers.
• Both forms are due to fungal spores.
• These forms of rot need moisture content to grow and spread.
• Both forms of rot cause damage to the timbers.

What is the Difference Between Wet Rot and Dry Rot?

Wet rot is a form of fungal decay that requires a higher moisture content to grow, while dry rot is a form of fungal decay that does not require a higher moisture content to grow. So, this is the key difference between wet rot and dry rot. Furthermore, wet rot is due to the fungal spores of Coniophora puteana, whereas dry rot is due to the fungal spores of Serpula lacrymans.

The below infographic lists the differences between wet rot and dry rot in tabular form for side by side comparison.

Summary – Wet Rot vs Dry Rot

Timber is widely used in houses and buildings that can be vulnerable to decays. One of the main threats to structural timber is wet rot and dry rot. Wet rot and dry rot are common forms of fungal decay found in timbers. Wet rot requires a higher moisture content to grow, while dry rot does not require a higher moisture content to grow. Thus this is the key difference between wet rot and dry rot.

Reference:

1.“How to: Identify and Treat Dry Rot and Wet Rot: Find a Surveyor.” RICS, 17 Aug. 2017.
2. “Causes of Rot: Help & Advice: Rentokil Property Care.” Causes of Rot | Help & Advice | Rentokil Property Care.

Image Courtesy:

1. “Wet Rot (995020497)” By Jason Hollinger – Wet RotUploaded by Amada44 (CC BY 2.0) via Commons Wikimedia
2. “Deck beam dry rot” By SFW Construction – www.sfwconstruction.com (CC BY-SA 4.0) via Commons Wikimedia