What are the code requirements for installing manufactured stone on the exterior of the wood stud wall of a house?
Tuesday, January 22, 2019
It is called “adhered masonry veneer” at Section 1405.10 of the Florida Building Code (FBC), and the International Building Code (IBC) is similar. The water-resistive barrier and lath are the same as for stucco. But here are the specific differences with manufactured stone:
1) Flashing - Should comply with Section 1405.4, with the addition of the following.
1405.10.1.2.1 Flashing at foundation.
A corrosion-resistant screed or flashing of a minimum 0.019-inch (0.48 mm) or 26 gage galvanized or plastic with a minimum vertical attachment flange of 31/2 inches (89 mm) shall be installed to extend not lessthan 1 inch (25 mm) below the foundation plate line on exteriorstud walls in accordance with Section 1405.4. The water-resistive barrier shall lap over the exterior of the attachment flange of the screed or flashing.
2) Clearances - Minimum 4 inches above ground, 2 inches above paved surfaces, or 1/2 inch above exterior walking surface that is supported by same foundation as exterior wall.
On exterior stud walls, adhered masonry veneer shall be installed not less than 4 inches (102 mm) above the earth, or not less than 2 inches (51 mm) above paved areas, or not less than 1/2 inch (12.7 mm) above exterior walking surfaces that are supported by the same foundation that supports the exterior wall.
At some homes, we see that there once was 4” between the bottom of the stone and ground, but infill of soil and mulch for landscaping has reduced or eliminated it.
3) Scratch coat and adhering veneer - Minimum 1/2” scrach coat, completely covering the lathing and scored horizontally, followed by minimum 1/2” setting bed of mortar.
1405.10.1.4.2 Scratch coat.
A nominal 1/2-inch-thick (12.7 mm) layer of mortar complying with the material requirements of Sections 2103 and 2512.2 shall be applied, encapsulating the lathing. The surface of this mortar shall be scored horizontally, resulting in a scratch coat, with a minimum of 3/8” setting bed after manufactured stone is applied.
1405.10.1.4.3 Adhering veneer.
The masonry veneer units shall be adhered to the mortar scratch coat with a nominal 1/2-inch-thick (12.7 mm) setting bed of mortar complying with Sections 2103 and 2512.2 applied to create a full setting bed for the back of the masonry veneer units. The masonry veneer units shall be worked into the setting bed resulting in a nominal 3/8-inch (9.5 mm) setting bed after the masonry veneer units are applied.
Heres an example of an inadequate scratch coat and adhering veneer below.
The building science guru Joe Lstiburek likes to call manufactured stone veneers “lumpy stucco,” because it's really just stucco with stuff stuck into the second, setting bed layer. Once you think of it that way, all the code requirements begin to make sense.
Also, see our blog post What is the average life expectancy of manufactured stone?
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To learn more about exterior walls and structures, see these other blog posts:
Diagrams - Installation Guide and Detailing Options for Compliance with ASTM C1780 for Adhered Manufactured Stone Veneer, Masonry Veneer Manufacturer’s Association
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