Stone and Synthetic Stone
A Traditional Look That Requires a Drainage Mat and Vapor-Impermeable Sheathing
Wood-frame walls can be veneered with stone
Facing a wood-framed building with stone or synthetic stone is a good way to get the look of traditional masonry at a lower cost than traditional construction methods. Both materials are fire and insect resistant, need very little maintenance, and are among the most durable wall claddings available — as long as flashing and moisture details are well thought out and executed.
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Use better masonry ties
Two-piece adjustable masonry ties are better for two reasons:
Masonry ties can be either galvanized or stainless steel. The stainless-steel ties cost more, but over time, galvanized types can corrode. This is particularly true in coastal areas.
Stone is natural and durable — but heavy
In many places, stone can be collected in fields and woodlands without completely disturbing the natural landscape. It will more often come from quarries that can greatly change landscapes and damage ecosystems. Because of the cost of transporting what is generally a very heavy material, it is usually sourced locally. This may make it easier to investigate how responsibly the stone was collected and processed.
You can't find a material much more durable than stone (although sedimentary rock like sandstone can suffer frost damage and other types of erosion). Other than pointing mortar joints, a well-built stone facade should be virtually maintenance free for decades, if not longer. If used to cover a foundation or even the entire first floor, it can really ground a house. The type of cut and installation can range from round and rustic to clean and contemporary.
Don't make it obvious that the stone is fake
One common design error with adhered manufactured stone veneer is to install the siding on walls where traditional stone would not work. The classic error is to put stone veneer on the sides of a cantilevered bay window or on dormer cheeks. With no apparent foundation to support the load of the "stone" wall, such installations look ridiculous.
Following manufacturers' instructions will not guarantee success
Because of liability concerns, the problem of oriented strand board (OSB) rot behind adhered manufactured stone veneer has not yet been fully acknowledged by producers of manufactured stone. Builders should not assume that manufacturers' installation instructions adequately protect sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. from rot.
The proper installation of masonry veneer is covered in IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code. Section 703.7, with common installation details shown in accompanying Figure 703.7. All masonry veneer must be over an approved water-resistant barrier and anchored to the underlying substrate with corrosion-resistant metal ties spaced a maximum of 24 inches vertically and horizontally (703.7.4). Additional ties are required around window and door openings (703.7.4.1.1). The veneer should be separated from the sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. with a 1-inch to 4 1/2-inch air space (703.7.4.2), or alternatively, the space can be filled with mortar or grout (703.7.4.3).
Flashing directs infiltrated water
Corrosion-resistant flashing must be installed between any means of support and the first course of brick or stone above it (703.7.5) and include 3/16-inch weep holes every 33 inches immediately above the flashing (703.7.6). Flashing must also be installed over windows and doors, over projecting wood trim, above roof intersections, and anywhere that wood framing interrupts or attaches to the veneer, including porches, decks, and exterior stairs (section 703.8). Seismic activity in the area and the percentage of exterior walls covered by structural sheathing may limit the veneer's height and weight (Table 703.7).
Rules differ for manufactured stone
The installation methods for manufactured stone veneer varies by product, so code officials will likely refer to the manufacturer's printed instructions.
ABOUT STONE AND SYNTHETIC STONE
Stone veneer that is 8 inches thick weighs 6 tons or more per 100 square feet. Stone veneers must be set on a solid masonry ledge built into the concrete footing, which means more concrete than for an unveneered foundation. Setting stone is labor-intensive, and skilled masons may not be as easy to find as carpenters who can install other types of siding.
Manufactured stone is lightweight concrete that has been molded and colored to look like building stone. It costs one-third to one-half as much as real stone veneer, and it’s light enough to adhere to a wall without any special footing for support.
Manufactured stone is made in a variety of colors and patterns but, unlike natural stone, the coloration is only on the surface, so cut edges must be concealed in the mortar joint.
MORE ABOUT STONE AND SYNTHETIC STONE
Many unwary builders have been plagued by callbacks after installing natural or manufactured stone veneer over OSB sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. . Installers typically apply wire lath over two layers of #30 felt and adhere the natural or manufactured stone to the wall with mortar. This installation method, however, has been associated with a rash of catastrophic failures, especially on walls with OSB sheathing. Unless a three-dimensional drainage mat or dimple mat is included between the two layers, little drainage may result.
Stone veneer and manufactured stone are reservoir claddings, meaning that they absorb and hold water after a rainstorm. Once the sun comes out, the wet cladding tries to dry in both directions, which can push moisture into the building, a process called inward solar vapor drive.
A well-detailed stone veneer installation requires vapor-impermeable sheathing to slow inward solar vapor drive. In most cases, extruded polystyrene or polyisocyanurate foam are the best sheathings to use under stone veneer. Vapor-permeable sheathings like Celotex should never be used behind stone veneer.
The best installations will include a rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. gap between the manufactured stone veneer and the wall sheathing. NAHBNational Association of Home Builders, which awards a Model Green Home Certification. has published an excellent resource with details on this type of installation; the document is titled "Improving Drainage and Drying Features in Certain Conditions: Rain Screen Designs for Absorptive Claddings."
Building scientist Joseph Lstiburek calls manufactured stone "lumpy stucco." After investigating many walls with failed installations of manufactured stone veneer, he wrote an article ("Stucco Woes: The Perfect Storm") detailing his installation recommendations. Lstiburek's colleague, building scientist John Straube, has written a valuable report on adhered manufactured stone installations: "Adhered Veneers and Inward Vapor Drives: Significance, Problems and Solutions."
See FHB #192, pp. 48-53, “Working with Manufactured Stone,” by Brendan Mostecki.
"Adhered Veneers and Inward Vapor Drives: Significance, Problems and Solutions," by Dr. John Straube.
- Dan Thornton/Fine Homebuilding #192
- Chris Ermides/Fine Homebuilding #192
- Justin Fink/Fine Homebuilding #192