Q A brick masonry veneer wall has a little less than half the brick depth supported by shelf angles in some locations. The bearing on the shelf angle varies from 1½-in. to 2½ in. The support is less than 2 in. in about 75 % of the building. We cannot find any indications of distress on the three-year-old building.
Do the walls need to be torn down and rebuilt with longer shelf angles that support at least half of the exterior wythe of brick masonry?
A If there are no other signs of distress, I would not remove the brick masonry just to increase the bearing of the masonry on the shelf angle. In reality, the masonry in most of these walls is primarily supported by just the back portion of the angle anyway.
The angles deflect as the masonry walls are built and the loads are applied. As the masonry load is applied to the angle, its tip moves down away from the underside of the brick and flashing above as it deflects. The brick masonry wall above sets up, is stiff, and is unable to follow the rotation of the angle. Without contact, there is no load transfer. Therefore, in most cases, only the back portion of the brick is supported by the shelf angle.
The biggest problem with having less than half the brick supported by the shelf angle occurs during construction. It is difficult to install the brick since they will fall off the angle. Wood shims can be used to temporarily support the new brick veneer off the top of the masonry wall below until the masonry is set. As long as these shims are eventually removed, the expansion joints still function properly.
Unfortunately, I have also seen buildings where mortar was used to support brick units above the shelf angle with less than half bearing. In these cases, the mortar was not removed. The mortar bridges the horizontal expansion joints beneath the shelf angles, which leads to problems associated with differential movement.
If there was considerable damage to the masonry due to minimal support, it may be possible to replace the shelf angles without rebuilding all the brick. Brackets or shear pins can be installed to support the masonry above the shelf angle. The shelf angle and flashing is then replaced and the load of the masonry above transferred back into the new shelf angle when the brackets or shear pins are removed.
One obvious problem with this approach is that the band of replaced masonry may not match the remaining brick. This result is sometimes the case even if the same brick and mortar type are used.
Q My company is designing a cavity wall with brick veneer and 6-in. concrete masonry back-up. The wall system will have a 4-in. to 4½-in. cavity space filled with 2-in. rigid insulation. At the window openings, the brick returns to the exterior face of the CMU to allow the aluminum windows to be set back 7-in. from the face of the masonry. Obviously, the insulation will be disrupted at these brick masonry returns.
Will the thermal short created by the brick returns at the window jambs be enough to cause any problems?