I am about to have a zero clearance gas fireplace installed. I thought I would need to coordinate my sheetrocking of the wall with his framing for the wall thimble. When I called to ask him about it he said to go ahead and sheetrock the entire wall and that the wall thimble didn't need to be framed. I was skeptical and asked him a few times in different ways but he insisted and so I figured he knew what he was talking about. Is it acceptable to use the wallboard and sheathing for support? Could he have meant that it would be framed after the fact and that it didn't need to be framed prior to sheetrocking?