I had water/insect damage to a wall under a window. I believe I have solved the water problem and have replaced the studs, sill plate etc. When the new insulation is in place can I/should I cover it with plastic before I put up sheetrock - or will that make moisture retention worse?

Is this wall above or below grade? Fopr above grade installation no plastic is recommended but the insulation should have a good vapor barrier facing toward the heated room. Plastic is not going to wreck your job, its just not needed.

Can I install sheet rock directly over existing tile in a bathroom?

Marylou, you can start your own post by clicking ASK. This will be less confusing for usbecause we can't have two topics going at the same time. And no you should not.