Below-grade space in Huntsville
Full basements are less common in Huntsville than crawlspaces and slabs, but where they exist, and in every crawlspace, the same forces apply: water from heavy rain, humid air, the ground itself, and radon.
Radon
The Alabama Department of Public Health lists Madison County among 15 Alabama counties with the highest potential for elevated radon. It also notes that levels can differ greatly even between neighboring houses, recommends that every home be tested, and points to fixing homes at or above 4 pCi/L. If you're finishing a basement, test before you start; a radon system is easier to install before the walls and ceiling go up. A typical system uses a pipe and fan to pull soil gas from under the slab and vent it above the roof.
Limestone ground
The Geological Survey of Alabama notes that much of north Alabama sits on limestone and other carbonate rock that can dissolve and form caves and sinkholes, and it lists drainage problems and heavy rainfall among the things that can trigger a sinkhole. For a basement, that means water handling is more than a comfort issue. Downspouts and surface water should be carried well away from the house rather than dumped beside the foundation. If you notice a depression forming in the yard near the house, have it looked at before you add a drain or regrade.
Heavy rain
NOAA's engineering weather data for the Huntsville airport station lists a 100-year rainfall rate of 3.5 inches per hour. A sump pump sized for ordinary storms can fall behind in rain like that, and a power failure during a storm stops it entirely. Ask the contractor about pump capacity, a backup pump or battery backup, and where the discharge line ends; it should drain away from the house, not back toward it.
Humidity
NOAA counts about 935 hours a year in Huntsville with the wet-bulb temperature above 73°F. Warm, humid outdoor air coming into a cool basement or crawlspace condenses on cold surfaces, which is why so many have musty smells in summer. Venting a crawlspace to outdoor air in July can make it wetter, not drier. Ask what the contractor recommends: a sealed crawlspace with a vapor barrier and dehumidification, or another approach, and why.
Before you hire
Ask for a written scope that separates drainage, waterproofing, vapor control and radon work, so you can compare bids line by line. Ask who handles permits for any finishing work, and ask for references from jobs at least a few years old, since water problems take time to show.