Masonry Fireplace: How It's Built, Code Clearances and Upkeep
Updated · By the Roof to Footing editors
A masonry fireplace is a fireplace built on site from brick, block or stone, with a firebox lined in firebrick and a masonry chimney above it. It's the traditional wood-burning fireplace, and it's different from a factory-built (prefab) fireplace, which is a metal box with a metal flue that comes as a tested, listed unit. A well-built masonry fireplace can outlast the house; a neglected one is a fire and water hazard.
Parts of a masonry fireplace
From the bottom up:
- Foundation and hearth slab: concrete footing that carries the fireplace's weight, which can be many tons.
- Hearth and hearth extension: the noncombustible floor inside the firebox and in front of it.
- Firebox: the burning chamber, lined with firebrick set in refractory mortar.
- Throat and damper: the narrow opening above the fire, with a chimney damper.
- Smoke shelf and smoke chamber: where smoke slows and turns into the flue.
- Flue liner: clay tile, cast-in-place or stainless liner inside the chimney.
- Chimney, crown and cap: the masonry stack, its chimney crown and a cap over the flue.
Key code dimensions (2021 IRC)
| Item | Requirement (summary) |
|---|---|
| Firebox depth | At least 20 inches (Rumford fireplaces have their own rules) |
| Hearth extension, opening under 6 sq ft | At least 16 inches in front and 8 inches beyond each side |
| Hearth extension, opening 6 sq ft or more | At least 20 inches in front and 12 inches beyond each side |
| Clearance to combustibles | Wood framing kept back from the masonry, with specific clearances for trim and mantels |
These come from IRC section R1001. Local codes may differ, and fireplace work usually needs a permit. A mason and the building inspector will work from the current local code.
Masonry vs. prefab
| Masonry | Factory-built (prefab) | |
|---|---|---|
| Construction | Built on site by a mason | Listed metal unit, installed per instructions |
| Weight | Very heavy; needs its own footing | Light; sits on the floor framing |
| Lifespan | Decades to a century with upkeep | Often 20 to 30 years |
| Heat | Masonry stores heat and radiates after the fire | Less thermal mass |
| Cost to build | Much higher | Lower |
| Chimney top | Concrete crown | Metal chase cover |
Annual upkeep
- Inspection and sweeping at least once a year, more if you burn often. Creosote buildup in the flue is what causes chimney fires.
- Check the crown and cap for cracks and damage.
- Look at the firebrick for cracked bricks and open mortar joints; repair with refractory mortar.
- Check the damper for rust and a good seal.
- Burn dry, seasoned hardwood. Wet wood makes more creosote and less heat.
Making one more efficient
An open masonry fireplace sends much of its heat up the chimney. Options to get more from it:
- Glass doors to cut room-air losses when the fire burns down
- A top-sealing damper to stop drafts when it's not in use
- A wood stove or fireplace insert with its own stainless liner, which can turn the fireplace into a real heat source
- Gas logs, as long as the damper is fixed open
If you're thinking about a fireplace open on more than one side, see three-sided fireplace; those are usually gas units for good reasons.