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ARCH 2614/5614 Lecture notes

Jonathan Ochshorn

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Wall sections: Brick/stone veneer

This lecture covers brick veneers (two common cavity wall systems) and stone veneer. The two brick systems are as follows:

Brick veneer

Woody Harrelson, in Indecent Proposal, completely mangles the legendary speech given by Louis Kahn to students at Pratt in 1973 ("You say to the brick, 'What do you want, brick?' And brick says to you, 'I like an arch.'") by conflating the plight of the brick with his own personal struggles ("Louis Kahn said, 'Even a brick wants to be something. [showing slides of mostly stone architecture...] A brick wants to be something. Aspires. And a common ordinary brick wants to something more than it is, wants to be something better than this [holding a lowly brick in his hand]. That is what we must be.")

BV/SS

The following diagram illustrates the system, using steel studs as a back-up wall. The purpose of the back-up wall is to provide lateral support for the single wythe of brick that acts as the cladding. It accomplishes this task as follows: metal wall ties are inserted into the mortar joints of the brick courses (at a spacing of approximately 1 tie per 4 square feet of wall surface area, or about two feet apart in each direction), which then span the cavity and fasten to the stud wall. Some early steel stud back-up walls, using light-gauge metal studs, were not stiff enough to prevent cracking of the brick veneer during high winds; heavy=gauge studs are needed to provide adequate stiffness in the back-up wall. If the cavity is insulated, the ties must penetrate the insulation. In any case, they are fastened to the studs themselves, and not to the sheathing, although they penetrate the sheathing to get into the studs. Flashing is shown beginning at the back up wall (possibly as an extension of the air barrier material) and coming over the shelf angle, where it should protrude as a "drip edge" over the joint. Flashing material is traditionally made of corrosion-resistant metals, but can also be fabricated as "fabric flashing" consisting of rubberized membranes. In the latter case, a metal drip edge should still be adhered to the fabric flashing where it extends beyond the surface of the cladding.

diagram of SS/BV cavity wall showing shelf angle, flashing, wall ties, brick veneer, and steel stud back-up wall

Note that in the case shown above, the back-up wall is supported directly on the structural slab. It is also possible for the steel stud back-up wall to bypass the structure, as is shown in the image below (left). Case (a) shows the back-up wall cantilevered from the structure and bypassing the structure; while case (b) shows the back-up wall spanning from one slab to the underside of the structural girder above. Note that in the latter case, the top support for the back-up wall must permit "sliding" of the wall up and down relative to the position of the structure, i.e., only supporting it laterally. The photo on the right shows the addition to Lincoln Hall at Cornell University during construction of the steel stud back-up wall.

diagram of alternate SS/BV cavity wall systems, with one having the steel stud wall in front of the slab, and the other with the steel stud wall directly on the slabLincoln Hall Addition, Cornell University, under construction, showing steel stud back-up wall

Metal wall ties can be purchased that are coordinated with the insulation within the cavity; that is, they simultaneously hold the insulation in place and provide a lateral tie to the brick. In the proprietary system shown below (X-Seal), the tie can move vertically to accommodate differential movement between cladding and structure, but resists lateral movement of the brick veneer. Note how the tie is embedded within the brick mortar joint.

advertisement for X_Seal showing wall tie system for brick veneer

BV/CMU

The more traditional use of concrete masonry units (CMU) to back up brick veneer in a cavity wall is similar in section to the use of steel studs. The CMU wall is typically constructed on the edge of the structural slab. Special wall ties provide horizontal reinforcement in the courses of the CMU wall, while also "reaching out" across the cavity to tie the brick veneer to the backup wall. For that reason, the course elevations of the CMU must be coordinated with those of the brick, both systems using an 8" vertical module. An example of such a coordinated system is shown below (left). A more routine example of brick veneer being installed over a concrete and CMU wall (right) is shown on College Avenue, Ithaca, NY (photo by J. Ochshorn). Note the steel shelf angle fastened to the reinforced concrete wall and girder.
example of CMU-brick tie systemphoto of BV/CMU system being constructed


narrator image
See National Lime Association video excerpt.


End dams

Where windows are inserted into a cavity wall, flashing covers the cavity over the window, so that water cannot enter the building at that point. Additionally, flashing is typically placed under the window sill, for the same reason. In this latter case, the ends of the flashing are turned up, forming a dam, so that water is prevented from moving horizontally across the flashing and entering the building through the window assembly. Note that the idea of flashing across the cavity is problematic, as water may travel horizontally on the flashing, finding seams or other openings, and in that way get into the building. Poorly detailed or installed flashing, or drip edge details, can also lead to such building failures (see image below)
comparison of
"Ideal" detail from Architectural Graphic Standards (1981) without any drip edge compared with actual, poorly installed, application of drip edge and sealant (Addition to Statler Hall, Cornell University, photo by J. Ochshorn)

See Masonry Detailing Series drawings produced by the International Masonry Institute.

Stone veneer

Thin stone can be used as a veneer over a back-up wall. The primary differences between the use of stone and brick as a veneer (cladding) are as follows:

schematic stone fastening strategies

freedom of movement at corners of typical cladding panel

Case study: Milstein Hall Stone Veneer (and aluminum soffit panels)

Milstein Hall detail section at fascia


video link