Dry rot is not inevitable, but it is common in many homes, apartments, and other structures with wood siding and trims.
The first key to avoiding dry rot is to select quality wood. But a second vital component is proper priming, sealing, painting, and flashing when applicable.
Unfortunately, the quest to maximize profits on the part of builders, especially spec builders, often tempts them to use materials (such as exterior wood trim) that are vulnerable to dry rot.
Not to mention eventual twisting, warping, and cupping – that also enhances the potential for dry rot.
A common oversight in the installation process of any exterior wood trim is when the painter fails to back prime (in addition to the edges and front surfaces) before the installation of the trim.
Back priming limits, the intrusion of moisture through the wood, which lessons the progression of dry rot and serves to equalize the penetration of moisture, which will subsequently lessen the wood’s propensity to warp or cup.
More on back priming
Wood is most susceptible to dry rot when a moist condition continues for extended periods.
Since the inside face of the wood trim is sandwiched firmly against the wood siding, the space between the two surfaces remains moist long after a rainstorm has passed – becoming the perfect breeding ground for not only dry rot but mold and fungus.
In addition to wood trim, the same potential happens anytime two exterior wood surfaces are tightly abutted.
If your exterior trim has not yet developed dry rot, you can preserve and protect the existing wood trim by the application of elastomeric caulking along all vertical and horizontal edges, followed by repainting with high-quality exterior paint.