Dry rot damage to sub-floor.

Dry rot damage to sub-floor. QBIS. Condensation is occuring to the underside of this timber floor from evaporation of water that has ponded on the soil below. This is causing the timber to decay.

Dry rot damage to sub-floor of house

Dry rot to timber of a sub-floor area.


Dry rot is caused without direct water contact.

  • From evaporation of water in or on the soil.
  • Ponding of water to the sub-floor area from seepage, surface water and/or leaking plumbing.
  • Main cause is from condensation of moisture on timber occurring consistently, over a long period of time.
  • Insufficient clearances between timber and the soil.
  • Inadequate cross flow ventilation (from all sides of the sub-floor) not allowing proper flow of the air to remove water droplets forming on the timber.

Combination of these problems causes fungal decay of the timber over a period of time.


Without removing all affected timber and creating appropriate ventilation and ground clearances, there is no effective long term rectification.

  • Fitting an appropriate drainage system, this may cause problems with movement.
  • Fit more ventilation to sub-floor area of the house to allow cross flow of air.
  • Fit mechanical ventilation system, not recommended.
  • Lower outside paving and soil levels, around the house.
  • Create required clearances between all timber and soil.

In most cases, an effective, economical rectification cannot be achieved without major reconstruction, at a great expense.

Dry rot damage to sub-floor

Important notes: 

  • Dry rot is often confused by the uninformed, with wet rot. Wet rot is caused from leaking as opposed to condensation from ponding of water below.

Dry rot can cause health problems with inhabitants of buildings, especially if they already have a breathing problem.

Related Information:

Wikipedia Dry Rot

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