Masonry Veneer: Using Masonry Veneer with Multi-Story Wood Framed Construction

Podium-style building: 2 stories reinforced concrete and steel construction, with 5 stories wood framing above – all to be clad in masonry veneer.

Building codes have changed in recent years to allow use of wood-framed construction on mid-rise buildings. For many years this type of construction was predominately concrete frame or reinforced masonry construction, and masonry veneer was anchored to the concrete masonry backup, supported at each floor line with a steel shelf angle.

Designers are stretching the limits of what the code allows, and now it is common to see 4, 5, or 6 story buildings having steel framing or a reinforced concrete podium at the first floor (and sometimes also at the 2nd floor), with up to 5 stories of stick framing above. This form of construction is gaining favor as being cost-effective, but there are several challenges to making the masonry veneer work in harmony with the wood framing. If you are hired to lay up a masonry veneer over several stories of wood framing, make sure the design incorporates these ideas.

Shelf Angles

TMS 402, Building Code Requirements for Masonry Structures (Chapter 12), prohibits supporting more than 12 feet of veneer on wood construction. To get around this requirement some designers are supporting up to 45 feet of veneer on a shelf angle connected to steel/concrete at the top of the podium level. This means using a very heavy angle to meet code deflection requirements.

The building code also prohibits supporting more than 30 feet of veneer on a shelf angle, but there are some building code officials that permit this practice if “alternative design” can prove that structural and differential movement considerations are satisfied.

This 3rd floor brick sill was installed with a slope. Over time, the window moves downward along with the shrinking wood framing, and the brick veneer expands, pushing upward. Bricks that were tucked up under the window frame are rotate and crack in response to this movement.

Differential Movement

Brick veneer always moves relative to the structural stud wall. Clay bricks expand as they absorb moisture after firing, and brick masonry expands with an increase in temperature. Adding these two effects together, you can expect each 10-foot story of brick masonry to expand about 1/8 inch.

Wood framing also responds to variations in moisture content, swelling in high humidity and shrinking at times of low humidity. Most shrinkage actually occurs as cross-grain shrinkage at sill plates, with less shrinkage parallel to the length of wall studs. Wood framing shrinkage can be in the range of 0.08 to 0.15 inch over a typical 10-foot story height.

With brick expanding and the wood framing shrinking, you can expect to see differential movement between the two materials in the range of 1/8” to ¼” for each 10-foot story height. That doesn’t sound like much, but there are some designers supporting 4 stories of veneer off a shelf angle at the podium level. Over the 40-foot height of brickwork, you will see as much as 1 inch of differential movement between the wood stud wall and brick veneer.

Special details will be needed at windows, doors, vents, and other penetrations to accommodate this movement. Windows will move downward as wood framing shrinks, and surrounding brick veneer will be expanding upwards. Sealants cannot handle this much deformation and special cover plates are needed to maintain weather resistance at joints around windows.

ore problematic are brick sills installed to butt up against window sills. Rowlock sills will crack and rotate as the veneer moves upward relative to window framing (Figure).

A completed mid-rise building with CMU and brick veneer over wood framing.

Structural Deformations

Similar movement will occur as wood framing deflects under structural loads. Stud walls deform much more than CMU backups, particularly under lateral wind and seismic loads. Movement joints have to accommodate this movement in addition to brick moisture and thermal expansion, and expansion joints may need to be as wide as 1 to 2 inches, depending on the structural layout. Again, this means architects need to design special movement joints with cover plates to maintain the weather enclosure. Expansion joints should be designed to be 4” off the building corners for best performance.

Veneer Anchors

All of this differential movement also means the you have to use adjustable veneer anchors throughout the façade. A standard hook-and-pintle anchor will work well for most situations, but they have to be placed with most of the hook extending down through the pintle. This will ensure that as the veneer expands, and the framing shrinks, the hook will not disengage from the pintle. Submit an RFI to the design team to make sure you are using a veneer anchor with a vertical leg that meets their design calculations for differential movement.

Construction Tolerances

There are no code-mandated tolerances for wood framing. On some recent projects the wood stud walls were 1” out per floor, resulting in highly variable cavity widths because the brick must be held plumb. Make sure this is discussed at the pre-construction meeting. Wood framing on these mid-rise buildings must be held to brick tolerances of ± ½-inch.