Structural Wood Is Rotting

Problem: Excessive moisture is causing wood in home to deteriorate.

Background: Decaying wood is more permeable to moisture, and therefore, is more subject to further damage and decay. Discoloration on wood may be mold (see Mold and Mildew Inside Home); however, symptoms of wood decay are also often recognized by color. Both white and brown rot are serious and deserve treatment or war rant replacement of the wood.

• White rot, the most difficult damage to recognize, is probably the worst form of wood decay. Wood with white rot appears somewhat whiter than normal, and sometimes has dark lines bordering the light discoloration. Though affected wood doesn’t always shrink or collapse, in advanced stages, some cracking occurs across the grain.

• Brown rot appears as a brown color or brown streaks on the face of the wood or end grains. In advanced stages, the wood looks very damaged, with the surface shrinking and collapsing and with cracks across the grain.

• Soft rot and blue stain are less damaging, slower-acting forms of wood decay that tend to be more active on the surface. With soft rot, the wood surface appears soft and profusely cracked, resembling driftwood in color. A blue stain indicates somewhat weakened wood, with blue, brownish black, or steel gray staining. The discoloration is not a surface stain; it penetrates the wood cells.

What to do: The most common method of detecting external decay is the pick test, using a sharp, pointed metal tool. An icepick, small chisel, or small screwdriver can be jabbed into wood and used to pry or lift wood slivers. A splintering break of wetted wood indicates sound ness, while a sharp break across the wood grain suggests decay. Decayed wood breaks out with less resistance, is easily penetrated by a pick, and may have a rough or fibrous surface. When cut with a saw, wood affected with even early stages of decay produces a rougher finish cut than wood that is not infected. When jabbing wood with a pick, start at ground level or below and work up. Check whether areas that look soft have other symptoms of decay, such as color and texture changes.

Special advice: Another test is to tap the wood’s surface; good, dry wood produces a sharp, clear, almost ringing sound and wet or decaying wood produces a dull, dead, soft sound.

Helpful hint: If you detect wood rot caused by excess moisture, try to correct the source of the problem, whether it is moisture from inside the house or moisture leakage into the house. You also may need to take steps to reduce humidity movement by stopping air leakage into wall, ceiling, and window cavities and by reducing high humidity with ventilation and membrane vapor retarders installed in crawl spaces, below ground walls, and basement areas.