Is it advisable to scrape remove all existing popcorn texture from ceiling before installing new sheetrock ? Some of the texture got wet and fell to the floor and some of the existing ceiling (about 30% of the area) deteriorated from being wet. Do not want to remove and patch replace the damaged areas. Would rather just put up new sheets, tap and bed the joints and finish texture the whole room. The room is 11' x 12'. The sheets will run the 12' length. I will use 1/2" x 4' x 12' to do the job. Thanks for your advice.

Drywall can cover a world of woes.

If the popcorn stipple is not too deep, then just go over top of it... assuming that there is only the one layer of drywall there already.

Three things to do first:
1) move any lights that you want moved... or install new boxes or pots. If you leave them where they are, then you can get box extenders to make the existing boxes flush with your new ceiling.
2) locate and then mark with a pencil on your stipple ceiling where the joists are.
3) use screws that are long enough to go through the existing ceiling into the joists.

I would scrape off as much popcorn material as possible. We use 3/8 sheet rock. Make sure you find straping at eash end then snap lines across as a ref. to install screws.

Have fun phil

I'd scrape as much as possible with a long handled floor scraper, don't have to be neat about it. I would also be concerned with mold, is the old stuff 100% dry and without mold.

Not an expert in this area.

We soaked the popcorn ceiling (1950's home) using a 2 gal pressure sprayer with hot water and a little fabric softener added, and then scraped it down. Not too tough at all.

Worked fine... the more it was soaked and let set, the more it practically fell off by itself.