Wood Rot

Wood rot is one of the most damaging forces on household wood in the world. Approximately 20 billion board feet of timber is destroyed by wood rot in the United States each year– far more than is damaged annually by fire! Replacement wood used to repair damage caused by wood rot accounts for almost 10 percent of the annual wood production in the U.S. alone.

What is Wood Rot?

Wood rot, also known as dry rot or brown rot, is wood decay caused by fungi.  When rot occurs, the fungi break down the components which give the wood strength and resilience. The wood is left weakened and brittle, often with a blocky appearance. Rot will only affect timber that is damp, typically with a moisture content in excess of 20 percent.

Basic Information

While it’s caused by tiny organisms, wood rot can cause large amounts of damage if not promptly repaired or replaced. The following information is a brief overview of wood rot and how it can affect you.

  • Although rot can occur in many places, the most common include bathrooms, decks, siding, crawlspaces, poorly designed and/or installed roofs, and around windows, sliding glass doors, and areas that contact soil.
  • We live in an area with extreme climactic variations, this can damage wood and create an ideal breeding ground for the fungi.
  • Failing to remove the rot-infested wood will result in the fungus spreading and causing additional damage. It could even provide an ideal habitat for pests that will compound the damage.
  • Damage can be confused with that caused by carpenter ants or termites. You can spot the former by the presence of clean cavities where the pests have removed wood and/or by spotting the insects themselves.


As you inspect your house, you should actively look for rot. It’s not always obvious; rot may occur below the outer surface of wood and underneath intact layers of paint.

If you suspect rot, use your fingers to press on wood surfaces and see if they feel soft or crumble easily. Use an awl or a knife to probe wood framing members. Typical trouble spots include:

  • Where two pieces of trim meet.
  • Siding butt joints, and where siding meets trim.
  • Horizontal surfaces, such as window sills, door thresholds, and railings.
  • Deck support posts.
  • Exterior stair stringers that support steps.
  • Fascia behind leaking gutters.


Preventing rot is simple. Do your best to limit exposure of wood in your home to moisture with these steps:

  • Siding – Have wood siding sealed properly.
  • Painting – Make sure any wood for outdoor use is primed on all 6 sides before painting.
  • Roofing – Have your roof checked once a year to identify and prevent and potential water damage, mold, or dry rot. Install gutters to direct rainwater away from your home’s walls and foundation.
  • Plumbing – Dry rot is commonly caused by plumbing leaks. Check underneath vanities and cabinets and around toilets for leaks. If you find any, have them repaired ASAP.
  • Ventilation – Make sure your bathrooms, attic, and kitchen have proper ventilation installed to remove excess moisture from the air.
  • Deck – Have your deck properly sealed. If you build your deck, have it built at a slight slope so water will shed easily.
  • Landscaping – Position lawn sprinklers so that they do not spray onto your home’s exterior trim.

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