If you peel off siding and the wood is dark brown and crumbly, what is the probable cause?

The indication of dark brown and crumbly wood after peeling off siding strongly suggests the presence of dry rot. Dry rot, caused by a specific type of fungus, thrives in damp environments where wood holds significant moisture. As the fungus breaks down the wood fibers, it weakens the structure, resulting in the dark discoloration and crumbling texture observed in the material.

In this scenario, while moisture damage is also a contributing factor to the initiation of dry rot, the specific condition of the wood being dark brown and crumbly aligns most closely with the distinct signs of dry rot. It's crucial to understand that dry rot doesn’t simply occur from any moisture exposure; it specifically relies on the presence of the fungi that consume the wood and lead to its deterioration.

Other options such as termite damage and pest infestation may cause structural issues, but they do not typically present in the same way as dry rot does. Termites create more visible tunnels and typically do not leave wood crumbling in the same manner, while general pest infestations would not specifically lead to the dark and crumbly appearance described. This distinction helps to pinpoint dry rot as the primary cause in this scenario.