HomeSmith LLC - Home Inspection, Remodeling & Construction Consulting Services
"From The Inspector"
Common Sense Advice & Technical Tid-Bits of Interest
Decay Fungi or "Rot" & "Dry Rot"
Wood products used in the construction of a home are susceptible to decay or "rot". However, if the materials are properly maintained, they can last for hundreds of years.
Wood rot is caused by the attack of  three basic types of fungi:
  • Stain
  • Mold
  • Decay
Stain and mold fungi mainly grow on the surface of the wood causing discoloration. By themselves, they do not weaken the wood, but their presence does indicate a moisture problem exists and warns of conditions which are favorable for the growth of the decay fungi. Decay fungi are microscopic threadlike plants that grow in the wood and attack the wood's cellular makeup. 
Physical changes in the wood may sometimes not be apparent on the surface. The changes can be detected by probing the wood with a screwdriver or ice pick. If the wood is in good condition the probe will not penetrate much farther than the surface. If the wood has deteriorated the probe will easily penetrate into the wood.
Wood that has been attacked by the decay fungus may be discolored, white and spongy or brownish and crumbly. The decay greatly reduces the strength and structural integrity of the wood. In the final deterioration stage the brownish crumbly rotted sections are often very dry. Some people will refer to this stage as "dry rot".
HomeSmith LLC
Gordon L. Smith
Home Inspector / Contractor
BTR# 50280 • ROC# 269134
The term "dry rot" is actually misleading. Rotten wood is often found in a dry condition and so it is called "dry rot", but the wood had to have once been wet for the decay to occur. More accurately it is the decay of seasoned wood caused by certain fungi capable of carrying water into wood they infest.
Unless the avenue of the moisture intrusion is sealed off and the infested wood removed, the deterioration will continue. 
Common Wood Rot Causes: 
  • close wood-to-earth contact
  • maladjusted irrigation system
  • excessive foliage against building
  • drain pipes splashing water onto framing
  • leaking plumbing
  • inadequate ventilation in crawl spaces
  • excessive ground water under the building
  • poor drainage 
Dehumidification Basics
Reducing and/or removing moisture from the air in the home is just as necessary as fixing a water leak. It is imperative in  preventing the growth of mildew and mold. Cool air will hold less moisture than warm air. Whenever the outside air is warmer than the inside air (especially if the air outside is humid) condensation issues are likely to arise. In order to eliminate condensation the air either needs to be heated or the moisture removed effectively and efficiently.
Dehumidifying Methods:
  • Cool the air. In a cooling system the humidity is reduced by cooling the air below the dew point.
  • Absorption of water vapor in the air. In one type of absorption system, the humidity is reduced with an absorbent material such as silica gel or a calcium chloride solution.
  • Desiccants are materials that are initially dry and will draw out moisture from the air and then release the moisture under controlled conditions which typically take place when the desiccant materials are heated.  
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommend "keeping the relative humidity in a home between  30-60%  to limit the effect of many unwanted conditions and harmful household particles". Also the Journal of Allergy and Clinical Immunology recommends "keeping relative humidity below 51% in order to deter dust mites and boost overall comfort of the home".
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