I hate crawl spaces! They are my least favorite place to go. Dark, dirty, often wet, sometimes so dry you can't breathe for the dust clouds. And they're usually filled with ducts, pipes, fallen insulation and electrical wires that I have to crawl over, under or around. At the same time they are one of, if not the most, critical components of a home inspection. Everything about the house relies on the foundation for support. If it fails, the whole house fails. I have to pay special attention to conditions because working in the dark can lead to missed clues and conditions.
A crawl space shows me the condition of the foundation. One of the most important things I'm looking for is moisture intrusion that can lead to rotting or warping of the wood structures like the sub floor, joists and the bottom plate (the wood laid on top of the foundation and to which the walls are attached). I also check the condition of piers and pilasters, the concrete or wood columns that support the center of the floors and the outer walls of the foundation. I will routinely take a carpenter's level with me to check for tilting piers or outer walls that may indicate a shifting foundation. Water intrusion can cause their soil to soften so they shift or tilt, producing a sloped or unstable floor, cracked walls and other bad stuff. If you see cracks at the corners of a doorway or window it could mean the foundation is shifting.
My routine is to crawl around the outside edges of the foundation looking for water trails and efflorescence (white mineral deposits) associated with moisture intrusion. At the same time, I examine wood surfaces for water trails, moisture stains and decay. Next I move into the center of the crawl space to examine pipe penetrations under the kitchen and baths. I've found more rotted and unsafe floors from leaks in those areas than I care to count. One was so bad that I beat a hasty retreat out of the crawl space for fear that the floor of was going to collapse. In another, the house itself appeared to be in good shape until I found the base of a brick fireplace in a state of near complete collapse from water damage.
I also check the condition of the floor insulation, usually fiberglass batts stuffed between the floor joists. These are important to the efficiency of heating and cooling system. Good ventilation and a plastic vapor barrier covering the soil are also essential to moisture control.
Except for a powerful light, my most useful tool is a simple screw driver for poking wet or water stained wood to see if it is firm and solid. I try to determine where the moisture is coming from and whether it is old, new or active. I routinely photograph the crawl space to give the client an idea of the conditions and to highlight specific issues I think are important. For safety reasons I wear a cap to protect my head from ever present nails, coveralls, gloves, eye protection, knee protectors and a respirator to protect me from dust, fungus spores and strands of fiberglass from the insulation.
I went to college. I have an MBA and lots of other education. I've learned something; there places I shouldn't go. I do not go into crawl spaces with standing water, especially if they have electric wires laying in them or If there are ducts, pipes or cables that I might damage or that might damage me. I've never come across a snake or other critter in a crawl space but if I did, I wouldn't go in until a snake chaser cleared it out.