Chimneys create a hazard when embers escape through the top. To prevent this, install spark
arrestors on all chimneys, stovepipes and vents for fuel-burning heaters. Use spark arrestors made of 12-gauge welded or woven wire mesh screen with openings 1/2 inch across. Ask your fire department for exact specifications.
If you’re building a chimney, use non-combustible materials and make sure the top of the chimney
is at least two feet higher than any obstruction within 10 feet of the chimney.