Extreme Condensation

On an inspection today, the home has a concrete front patio that was completely dry on top. The basement was extended under the patio. The under side of the concrete had so much condensation on it that it looked like it was raining in the basement. the steel beam supports were completely rusted and starting to crumble. Again there was no puddling or wetness on the top side of the concrete. Could all this rust and damage and moisture be caused by the cold weather outside and the heat in the basement. It was about 30 degrees today outside and about 70 degrees in the basement

Yes it can. Basic dew point scenario. That storage space needs to be sealed off and not heated or insulated to stop the mess.

How about a dehumidifier to lower the humidity . It also would add some heat . Put a drain hose to a floor drain so you never need to dump the holding tank…

The area has a sump pump installed. I just thought it was a lot of damage for condensation to cause. The steel beam had a lot of mineral build up and a ton of rust…

Iron will rust without condensation. Add in condensation and the process will speed up. How old is this iron? Very likely that the iron had a bit of rust before it was even installed. They store those things in the “yard” until used.

Why is it so hot in the basement?

What can hold more moisture, hot air or cold air?

The warmer the air, the higher the dew point. Which means condensation will form at higher outside wall temperatures.

No wall insulation and the metal beams conduct heat to the exterior cause your rain.

BTW: You control this by controlling the air, not adding insulation.