Cracks in stone veneer over a garage door: lintel sag, heat movement or foundation?

The question, posted on Reddit's r/Construction, describes cracking on a southwest-facing wall above a wide garage opening. Stone veneer over an opening like that usually rests on a loose steel angle. The International Residential Code requires at least 4 inches of bearing at each end of a veneer lintel and allows prescriptive spans up to 18 feet 3 inches, using a 5 x 3 1/2 x 5/16-inch angle shored for 7 days.

The Brick Industry Association's Technical Note 18 says deflection and settlement cracks taper. A sagging lintel leaves a crack widest at the steel that narrows to nothing as it climbs. BIA's lintel guide, TN 31B, caps deflection at 1/600 of the span and 0.3 inch, so over a 16-foot door the 0.3-inch limit governs. Settlement shows as diagonal, stepped cracking that starts near the foundation. Engineer Buck Durham, writing on the JADE Engineering blog, ranks sagging double-garage lintels second among causes of veneer cracks and says no rolled angle spans 16 to 18 feet under several feet of masonry without sagging.

Sun adds a third suspect. BIA says a dark wall facing the sun can reach 140°F at the surface while the air stays under 100°F. Its tables put structural steel at 6.5 millionths of an inch per inch per degree Fahrenheit and limestone at 4.4. Over a 100°F swing, a 16-foot angle changes length by about 1/8 inch. If its ends are packed tight in mortar, Durham says, the result is cracking at the upper corners of the opening. Rust is worse: BIA says corrosion products take up to 10 times the volume of the steel.

Before anyone caulks, mark the ends of each crack, date it and photograph it through a summer and a winter. Sealant over a joint that is still moving hides the pattern an engineer needs to read. Durham treats sticking doors, sloping floors or matching drywall cracks inside as signs of real foundation movement. Check the weep holes at the lintel and the angle for rust scale; the IRC spaces veneer weeps no more than 33 inches apart.