Masonry Design: Not-Quite-Through-Wall Flashing

Through-wall flashing is a common water management feature of masonry cavity wall and veneer construction. It is most effective if its outer edge is beyond the outer face of the wall and is turned down to form a drip edge and help water fall away from the joint under the flashing. It can be ineffective and result in leaks into a building if the outer edge of the flashing is concealed within the wall. In at least one case, a leak was attributed to flashing that stopped above the core holes of extruded brick. The design relied on the through-wall flashing to protect the building interior, but water which was intended to be conveyed out of the wall by the through-wall flashing was instead allowed to re-enter the wall and subsequently find its way to the building interior. Apparently, someone did not want to see the edge of the flashing coming out through the wall. At the time of construction it was common for the flashing to be coated with asphalt, and the asphalt coating - not especially attractive in any case - would melt under sunlight and over time it would drip and stain the face of the wall below. More attractive materials are widely used today, including drip edges of proprietary compositions or even stainless steel. The more attractive materials are likely to be more expensive. However, stopping the flashing within the wall may be the most expensive option of all, considering the possible costs of leak remediation.

Masonry Design: Separate hung masonry from foundation-supported masonry

When drawing up elevations for masonry walls, in addition to locating control joints (arguably "expansion joints") to accommodate expansion and contraction related to temperature and moisture, it is important to consider how masonry supported on lintels hung directly from deflecting structural steel will move differently from masonry that is supported directly by the building foundation. While "loose" lintels supporting masonry over openings usually rest on foundation-supported masonry at the ends of the spanned opening, hung lintels should be isolated from foundation-supported masonry in a way that allows for independent vertical movement related to deflection of structural steel. If the hung lintel overlaps the foundation-supported masonry, a soft joint similar to that below a relieving angle may be appropriate below the end of the hung lintel. And the control joint above the lintel should also be located to allow for independent movement of the two masonry conditions. Determining the location of the ends of the hung lintel is important for construction that will properly respect the different needs of the two conditions. It gets more complicated for hung lintel assemblies suspended from beams that are interrupted by columns. In any case, careful consideration should be given to the locations of control joints within the wall area that is supported by the hung lintels.

In some cases the best control joint locations for wall performance will not be the best locations for aesthetic intent. But, then, cracks are not usually attractive in appearance.

Masonry Design: A subtle difference in brick sizes

It may come as no surprise that bricks are available in different shapes and sizes. But, in at least one situation, the difference in size may be too subtle to notice until you see an area of infill that does not match the rest in coursing or joint thickness.

"Hey! Look at that small area of bricks with the fat mortar joints. What happened?"

Many U.S. buildings that are decades old were constructed of "standard" brick, each unit with an actual length of 8 inches. Today's "standard modular" brick of similar height and depth typically has a nominal length of 8 inches including the mortar head joint and an actual length of 7.625 inches, allowing for a .375 inch mortar head joint. (An actual length of 7.5 inches may also be available to accommodate a .5 inch head joint.) If you are renovating or adding to an existing brick building, it's a good idea to measure the existing brick. And, if you can't get a matching size, you may want to consider that in designing areas of infill.

(Similar issues can apply to matching existing brick color and bond. It may take a close look to spot a Flemish bond, a possible indication of underlying construction that differs from today's typical cavity wall or brick veneer construction.)