Understanding Chimney Construction
Proper chimney design and construction ensures safety and efficiency.
- Brick Requirements Standard brick: 3.5"×2.25"×7.5". Fire brick: 4.5"×2.5"×9". 7 bricks/ft² for single wythe. Double wythe: 14 bricks/ft². Add 10% waste factor.
- Sizing Guidelines Height: 3ft above roof penetration. Cross-section: 4"×8" minimum flue. Chase: 4" clearance to combustibles. Crown: 3" thick with 2" overhang.
- Material Specifications Mortar: Type N for exterior, Type S below grade. Fire clay mortar for firebox. Portland cement crown. Stainless steel flue liner: 0.019" minimum.
- Code Requirements UL 103 listing for factory-built. NFPA 211 clearances. ICC-ES evaluation. Local height requirements vary. Seismic bracing above roofline.
Construction Guide
Foundation Requirements
Footing: 12" thick minimum. 6" larger than chimney. 12" below frost line. 2500 psi concrete. Rebar: #4 at 12" O.C. each way.
Flashing Details
Base: 8" up wall, 4" on roof. Step flashing each course. Counter flash into mortar joint. Cricket required above 30" wide chimney.
Cost Analysis
Bricks: $0.75-1.50 each. Fire brick: $3-5 each. Mortar: $10/bag. Flue liner: $15-20/ft. Labor: $25-40/ft height. Permits: $200-500.
Maintenance Schedule
Inspect annually. Clean every 50 fires or yearly. Check crown every 3 years. Repoint mortar every 20-25 years. Replace liner if cracked.