I live in an older house. I need to replace what I thought was just drywall under my bedroom window. When I tore out the damaged section, it looks like there is a sheet of drywall behind a sheet of cement board. I am a DIY novice, so I have stopped my project until I have a better understanding of what I need to do. Does this sound familiar to anyone? I now am wondering if I need to install some sort of backer board then drywall, or just install a 3/4 inch sheet of drywall. Any info would be greatly appreciated. Thanks and Have A Great Day!
Unless this is a tiled wall there's no need for cement board.
If I had to guess I'd say that window has been leaking for a while and it's been repaired before.
If the other walls are plaster and lath they may have used the drywall as a shim to get the wall to come out even.
There is no 3/4 drywall that I've ever seen. May just have to shim out the studs and use 1/2" drywall.
It would be great if you could post a picture.
I'd be checking why that widows leaking, cheaking all over behind the walls for wood rot, fixing all that before messing with the drywall.