I am looking into building a new house with a woodburning fireplace, and trying to sketch out a design for cost workup that substitutes, for the all-masonry arrangement shown on the drawings, a zero clearance unit with framed outside chimney chase, veneered in real stone. Take a peek at my design, attached. Here are my questions.
1. My stone guy tells me to figure on a 6″ thickness of stone out from the plywood face of the chimney box. Does this sound about right?
2. It looks like the house framing will have the gable wall studded and framed and sheathed as if there is a big door opening where the fireplace unit goes. Do we do the opening, frame and sheathe, then do the chimney framing and attach to the house? Do we place blocking inside to pick up the chimney box walls where they tie in?
3. Note the one skew side of the chimney. I am thinking we’ll frame the straight side and chimney face in 2x4s, and use 2x6s on the skew wall. Any concerns about the skew wall with its 6″ veneer of stone?
4. I want this thing to look like the real thing, and am thinking we want to do the stone chimney cap and topcap like shown. The outside facewall bears down to a foundation, but the inside wall-over-roof (the stone facing shown as “area on roof side”) bears on roof. I’ll put another truss under it if I have to. At 2″ thickness, those caps and the 4 columns come to between 800 and 900 pounds. Any concerns?
5. For waterproofing, is shingle-lapped 15# felt, over the plywood sheathing, under the stone veneer, OK? It is going to be penetrated anywhere we attach the curly fry sheet metal ties.
6. I know, I know, “your codes may vary,” but how much of this chase will need to be rocked with 5/8″ gypboard on the inside? Only the side common to the house? Up to the roof line?