Every year a considerable sum of money is spent on repairing the structural damage caused by the fungal infestation commonly known and referred to as dry rot. Most of the damage is caused by a few species, but the dry rot fungus, Merulius Lacryman, is the most prevalent.

Dry rot fungus requires a constant condition of temperature and humidity. It thrives best in humid, unventilated places where the air is still and the wood is damp but not saturated. Dry rot spores will germinate on the surface of wood that has a moisture content slightly above 20% but is not really wet. The majority of fungi grow most rapidly at about 80-90 degrees F. Poor or improper ventilation in areas which can retain built-up heat often provide this ideal environment.

As with any fungus, the spores are ever present in the dormant stage, awaiting proper conditions to flourish. When germination occurs, a fine filament grows out from the spores. It subsequently gives rise to other similar filaments, which develop, into the vegetative portion of the fungus. At the same time, some of the filaments penetrate below the surface, first softening and then destroying the wood.

The appearance of the wood decayed by dry rot fungus depends on the stage of attack and the conditions under which the fungus has been growing. In a damp basement or crawl space, the fungus will produce masses of material resembling white fluffy cotton spread over the surface of the wood. In less humid atmospheres, the fungus forms a felted skin that may be pearly gray in color, with tinges of lilac or yellow.

Wood diseased by dry rot fungus has a scorched appearance, and in the final states, may readily break up into little square fragments or a dry powder. The parts of a house in which dry rot is most likely to be found are basements, crawl spaces, bathrooms, kitchens, and porches. Roof timbers may be attacked if there is persistent leakage.

To eradicate dry rot, the badly decayed wood should be removed and destroyed. Sound timber in the vicinity of the attack and timber used for replacements should always be treated with an efficient preservative. Finally and most important, the source of dampness responsible for the original attack should be eliminated.