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There is a BIG difference between a "fun guy" and a "fungi". And though "fungi" are considered a culinary delicacy, when found in your building framing, siding and trim, they cause dryrot, a form of wood "cancer". This kind of "fungi" is no fun. And like cancer, it's best to avoid the conditions that cause it. In the case of structures, the culprits are improper materials, flashing and design.

Dryrot’s name is a misnomer because the rot occurs in wet conditions, not dry. It occurs when water is allowed to penetrate wood in places and in a way where it won't dry out. Wood destroying fungi require a food source, oxygen and favorable temperature in order to survive. It’s a vicious circle: Moisture promotes fungi which increases wood permeability which allows moisture to penetrate further which encourages more decay, etc. etc.

There are three classes of dryrot:

  • Brown Rot Wood decayed by brown rot looks like dry leather and breaks easily into small cubical pieces. Wood strength decreases as the growth spreads. Most of the damage to structures is caused by brown rot.
  • White Rot Wood decayed by white rot often assumes a bleached appearance, frequently has black lines through it and feels spongy. Wood strength decreases gradually. If caught soon enough, white rot may be treated by bleach spray and scraped away. It is important to correct the moisture problem that caused the wet wood in the first place.
  • Soft Rot This looks like brown rot but the affected wood softens gradually from the surface inward developing cavities (invisible to the naked eye) within the wood cell walls.

In the fight against dryrot there are four prevention principles.

1. Build with properly seasoned wood. 2. Keep wood dry. 3. Break contact of wood and soil. 4. Where soil must contact wood, use properly pressure treated lumber.

The odor of mold and mildew inside the home is a sure sign of condensation and dryrot. Warm weather condensation can be reduced with fans and by decreasing the humidity of crawl spaces with adequate ventilation.

When mold and decay occur, the problem is either water conducting dryrot or dryrot growing on wet wood. Water conducting dryrot feels leathery and can often be peeled off in sheets. The other form of dryrot feels powdery or stringy. The only way to get rid of molds and decay fungi embedded in wood is to remove the piece. Frequently extracting a rotted structural piece can be an expensive proposition. Prevention is far cheaper. continued...

A common source of dryrot is wood decks. Decks themselves should be made of either cedar, redwood, sunwood or pressure treated lumber which all resist dryrot. The deck should have at least a 1/2" air gap between it and the siding that allows water to run down between. The deck should have positive drainage away from the building. The deck door should have proper flashing to prevent water intrusion. Indoor/outdoor carpet should be removed from the deck during the rainy or winter season since it traps moisture and promotes dryrot.

Windows and doors are a prime location for dryrot due to improper flashing and caulking. They all should have drip flashing over the top edge and proper caulking around all edges. Where there is more than a 1/4" gap, backer rod (flexible foam rope) should be laid into the gap and then sealed with a high quality silicon caulk.

Another major source of water intrusion that promotes dryrot is improper "kick-out" flashing. Kick-out flashing is found near the rain gutter where the roof meets a vertical wall. It "kicks out" rain water which runs along the vertical wall that would often miss the gutter and run behind the siding and get trapped in the wall. Missing kick-out flashing can cause huge dryrot damage. Have a competent roofing contractor check your roofs for proper flashing.

Avoid EIFS-Exterior Insulation Finishing System (also called "synthetic stucco" or "dryvit") like the plague. It is the siding that uses a foam board and specialty shapes followed by a plastic mesh and finally a coating that resembles stucco. It has a long history of trapping moisture in the walls and causing dryrot. If your buildings have EIFS, it should be inspected annually by a qualified EIFS inspection service using moisture scanning equipment. For more, see The EIFS Institute at https://www.eifsinfo.net.

Finally, do an annual inspection of all siding, trim and decks to detect dryrot in its early stages. Since it spreads like cancer, the sooner you remove it, the less costly the correction.

Deterrent is always the best policy when it comes to dryrot. But rather than watch your dryrot problem mushroom, declare war on the spores and never, never, never, never, NEVER give up.

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