Q: Another question please. Our contractor is saying that spray foam insulation on the basement ceiling is more efficient. Do you have any thoughts about this recommendation?

A: Hi XXXXX, spray foam has R5 insulation per inch whereas fiberglass is R3, so in that sense spray foam is more efficient.
However, spray foam sticks to the joists like glue (that’s the idea) so you can’t get it out if you need to get access to a pipe or wire. For this reason I do not recommend spray foam for the ceiling of a basement. 
Also, spray foam is more expensive per inch and per R value than fiberglass. So, economically, sprayfoam is less efficient than fiberglass. 
And, finally, the gas used to blow the bubbles in spray foam is 1,000 times more potent than CO2 at causing global warming. 
And, finally finally, spray foam is flammable whereas fiberglass is not. 
For all these reasons, I prefer fiberglass to spray foam for insulating the ceiling of a basement. 

And, really finally, fiberglass is porous to air which means that if some water does get into the fiberglass (like from an overflowing bath) it will evaporate and dry out. Spray foam is water tight which means any water falling onto the spray foam from above will sit there like a puddle with no ventilation and hence will take much longer to evaporate and dry out. This is risk for mold, rot and asthma for the people in the house.