What hearth extension means
The hearth extension is the noncombustible floor area in front of and beside the fireplace opening that catches sparks and embers.
Where it matters on a chimney job
Remodels that put wood flooring right up to the fireplace often break this rule. Check it before the flooring crew starts, so the fix is planned and not a surprise at inspection.
What the model code says
- The hearth extension runs at least 16 inches in front of and 8 inches beside the fireplace opening. (IRC 2021, Chapter 10)
- For openings of 6 square feet or more, it grows to 20 inches in front and 12 inches to each side. (IRC 2021, Chapter 10)
Check which code edition your building department enforces for hearth extension before you quote.
What it costs
Koira's fireplace installation cost guide puts a typical job at $2,400, with most between $940 to $4,400. The guide shows its sources and what moves the price. The fireplace installation cost calculator prices a job line by line.
Work it out
- Free calculator: Fireplace installation cost calculator
- Cost guide: Fireplace installation cost
- Tools, templates and guides: Free chimney resources
Sources: 2021 International Residential Code, Chapter 10, Chimneys and Fireplaces (ICC). Checked October 9, 2026.