Local fireplace installation in Nassau Village-Ratliff

Decorative tops need their own listing

A plain metal cap on a factory-built chimney can look out of place, and decorative shrouds are sold to dress it up. The code allows a shroud at the top of a factory-built chimney only when the shroud is listed and labeled for that specific chimney system and installed to the maker's instructions. A shroud that is not listed can trap heat or change the draft the system was tested with.

If you want a finished look at the top, we price a shroud from the chimney maker's list, or a chase finish that keeps the listed cap exposed. Anything else stays off the top.

Firebox depth and wall thickness

The firebox of a masonry fireplace is at least 20 inches deep under the code. Its back and side walls are 8 inches of solid masonry including a 2-inch firebrick lining, or 10 inches where there is no lining. Firebrick meets ASTM C27 or C1261, and the joints between the bricks, laid in medium-duty refractory mortar, stay no wider than a quarter inch. Those numbers are what keep the heat of the fire inside the masonry and away from the framing that sits a couple of inches beyond it. We lay the firebox before the smoke chamber, and the inspector can see the lining thickness at the opening.

The air space around a masonry fireplace

Framing lumber keeps a 2-inch gap at the face and sides of a masonry fireplace, and a 4-inch gap behind it. That air space has to stay open, except where fireblocking closes it at floors and ceilings. The code allows combustible trim and sheathing edges to meet the side walls and hearth extension only where they sit at least 12 inches from the inside of the firebox lining.

When we frame the wall around a new masonry fireplace, those gaps are measured before the drywall goes up, because they cannot be checked afterward. Where a gap is short, the fix is framing. Insulation or caulk will not do it.