Wood Rot

Wood rot is fungal growth in the cellular structure of wood. It is caused by placing wood in locations where moisture is present for long periods.

Wood rot can develop undetected in enclosed, poorly ventilated areas such as crawl spaces. The subsequent deterioration can lower the load bearing capacity of framing and, if not arrested early, wood rot can completely consume the wood members. Any wood surface with long-term moisture contact may develop the fungal growth, but the end grain, where cut wood cells are exposed, is the most susceptible.

Whereas the elimination of the moisture source will arrest further growth of the wood rot, prevention is by far the best remedy. This article addresses several problem areas and the appropriate preventive details.

Wood Stair Treads Should Not Be Buried in Stucco

  • Option 1: A stucco screed could be used to provide vertical separation between the wood stair tread and the stucco.
  • Option 2: A wood stringer held away from the stucco will allow water to flow through the assembly.

Finish Grade Too Close to Wood Structures

Uniform Building code, Section 2516(c)7, requires a six-inch minimum separation between finish grade and wood structures. Less separation poses a potential termite as well as wood rot problem.

Wood Star Stringer Deterioration

Untreated Douglas fir is commonly used for stair stringers that are placed directly on a concrete slab, and often this practice develops wood rot if exposed to moisture. The Uniform Building Code, Section 2516(c)7, requires a decay-resistant, or pressure- treated, wood for stair stringers placed on a concrete slab on grade.

Wood Balcony Railings Often Leak into the Building Frame

Railings often split and warp, generally offering little protection for the wall below.

An additional layer of barrier paper, or a product such as “Jiffy Sea,” should be installed over the standard building paper at the top of the wall. the barrier paper should lap down six inches on each side over the building paper.

Slope the top railing member to alleviate standing water.

All railing and trim members should be painted on all sides to reduce warpage and splits in the wood, including fresh end cuts.

Caulking and flashing should be used at intersections to prevent water entry.

Note: This article addresses concerns that relate to some common wood rot problems. There are a multitude of other conditions that can lead to wood rot damage.