I S S U E 1/2016 VOLUME 33 NUMBER 1 Journal of architectural technology published by Hoffmann Architects, Inc., specialists in the rehabilitation of building exteriors. Preventing and Treating Distress in Brick Veneer Cavity Walls Erin L. Kesegi, AIA and Robert A. Marsoli, Jr. M asonry construction is one of – clay brick – is actually a composite the oldest methods of creating built wall system, with materials ranging structures. However, the brick wall has from steel and concrete to flexible changed considerably since the first flashings and sealant, in addition to fired clay bricks were laid nearly 8,000 traditional brick-and-mortar elements. years ago. To address problems and How and where these materials come considerations with modern brick ma- together, and why they behave the sonry, it’s important to understand the way they do, is of critical importance components of the wall assembly, how to the weather protection, integrity, they behave, and what can go wrong. and longevity of the wall assembly. Today’s complex brick cavity walls As modern masonry construction has share little in common with the solid grown increasingly complex, so too masonry construction of Romanesque has the design, detailing, and installa- church towers or early load-bearing tion of brick cavity walls become more high-rises, with their thick, stout walls. demanding. Where once a skilled With multiple layers, or wythes, of mason was all it took to achieve a brick bonded together, these historic durable exterior wall, proper con- masonry walls relied on the unified struction now demands the efforts of structural capacity of the wall thick- multiple tradespeople working in col- ness to withstand horizontal and laboration with the design professional vertical forces and to provide weather to achieve a water-tight, structurally protection. stable, aesthetically appealing masonry In contrast, modern brick veneer exterior. Prevention of water infiltra- cavity walls anchor a single wythe of tion, structural failure, and other woes face brick across an air space, typically by means of appropriate design and two to four inches wide, to a back- meticulous workmanship is the ideal, Long, vertical cracks at building corners up material. Part of a drainage system but for existing buildings, the mission may indicate underlying structural distress. that includes flashings, drip edges, and becomes timely and accurate identi- weep holes, the air space creates a fication of emerging problems, with pathway for moisture to exit the wall repair strategies that provide lasting assembly, while a steel, concrete, or solutions. masonry back-up provides structural support. Design Basics What may seem on the outside to be As reinforced concrete and steel a wall composed of a single material framing have eliminated the need for Erin L. Kesegi, AIA, Project Architect, applies her expertise in building envelope remediation to addressing underlying causes of brick masonry distress. Project Manager Robert A. Marsoli, Jr. provides engineering services to resolve structural concerns for a range of building types, including brick masonry construction. JOURNAL load-bearing masonry, building design the brick veneer and the back-up, such flexible plastics, fabric, and composite in the twentieth and twenty-first cen- as at shelf angles, lintels, and the base metals. Given the projected lifespan turies has evolved new approaches to of the wall, flashing, a flexible, imper- of a modern wall assembly, it’s best to waterproofing protection. Early brick meable material, is used to collect wa- avoid materials that degrade quickly, walls relied on the mass and depth of ter and drain it to the exterior. Serving such as polyvinylchloride (PVC), which the masonry to absorb rainwater and both to direct water and protect the may last as few as five years. ambient moisture and to release it brick masonry from moisture dam- Water collected by the flashings is back into the atmosphere. Given the age, the flashing is in turn protected by drained to the exterior by means of nominal thickness of modern brick counter-flashings, which are attached weeps. While open head joints in the veneers, the mass of masonry is insuf- to or directly laid into the back-up. brick course above the flashings pro- ficient to absorb and release envi- At the face of the wall, drip edges, or vide a simple, effective weep system, ronmental moisture without allowing downward bends in rigid flashings, en- vents, screens, and other inserts may water penetration into the building courage water to form droplets that be used to disguise the open joints interior. Therefore, cavity wall design fall away from the wall surface, rather and prevent insect ingress. provides for a space between the back than travel back up under the flashing of the brick veneer and the face of the and into the wall assembly. Lateral Support back-up material, so that water that breaches the brick exterior can drain Copper, lead-coated copper, and stain- Masonry anchors secure the wall as- out of the wall system without reach- less steel are the traditional materials sembly to the building structure, while ing the building interior. for flashings, and they remain the most masonry ties connect multiple wythes durable and reliable options. However, of masonry together or join a mason- Flashing System and Waterproofing these materials are expensive, so flash- ry veneer to a back-up wall composed Where transitions must exist between ing now tends to be composed of of another material, such as concrete Typical Masonry Cavity Wall Wall tie Rigid insulation Air space Vertical reinforcing bar Brick Grout Mortar joint Moisture/air/vapor barrier membrane Concrete masonry unit Termination bar Horizontal joint reinforcement Mortar joint Flexible flashing membrane Cavity drainage net Weep vent / weep hole Metal drip edge Sealant bed Concrete foundation Illustration: David S. Obrizzo (adapted from the International Masonry Institute Masonry Detailing Series) 2 VOLUME 33 NUMBER 1 masonry units (CMU) or metal studs and shelf angles, along with adjustable walls is characterized by the type with sheathing. All of the metal acces- veneer anchors that allow the two and dimensions of the brick units, the sories for a masonry cavity wall should materials to move differentially within mortar type and tooling profile of be stainless steel and spaced at ap- their planes, while still providing an- the joints, and the coursing, or pattern, propriate intervals, as determined by chorage to resist out-of-plane forces, of the brick layout. In contemporary building codes, industry standards, and including wind and seismic pressures. brick cavity walls, the brick veneer is secured with metal wall ties to the the design professional. To accommodate vertical movement, back-up material. However, facade To control shrinkage cracks in ma- steel shelf angles (also known as reliev- designs may incorporate false headers sonry, as well as to tie multiple wythes ing angles) may be installed at intervals in the veneer to simulate traditional of masonry together and to anchor along the wall elevation, typically at coursing patterns. masonry veneers, horizontal joint re- each floor, to support the masonry inforcement is incorporated into the above a horizontal expansion joint, Brick size is standardized according to exterior wall system. Two or more allowing for vertical expansion of the “nominal dimensions,” which account longitudinal wires with perpendicular brickwork. Use of shelf angles depends not only for the size of the brick unit (ladder type) or angled (truss type) upon the type of structure, height itself, but for the completed assembly cross wires are laid in the mortar joint, of the building, size and location of in the wall system, including mortar with the longitudinal wires parallel to windows, type of masonry anchorage, joints. Bear in mind that openings, cor- the face of the wall. and a variety of other factors, including ners, and wall heights must take into building code requirements. account the dimensions and cours- Provisions for Movement ing using brick module, or increments Along with shelf angles, vertical and Building materials expand or contract based on the size of the brick. horizontal expansion joints are used to when exposed to external stresses, separate the masonry wall into seg- Mortar Joints such as changes in temperature (ther- ments and thereby prevent cracking. mal movement), moisture/humidity Regardless of the type of masonry As dissimilar materials in the assembly (moisture movement), dead and live construction, all brick units are held change in response to temperature, loads and external lateral forces (elas- together using mortar, a mixture of ce- moisture expansion, elastic deforma- tic deformation/creep). As brick draws ment, aggregate, and water that is but- tion, settlement, and creep, each will in moisture from its environment, it tered, or spread, between bricks during move according to its own tenden- will increase in size over an extended stacking. There is no single best mortar cies. Horizontal expansion joints are period of time. Most of the expansion type for all structures and situations, particularly important for masonry typically occurs in the first few months but a good maxim is to select the veneers attached to a reinforced con- after the brick is fired but continues at weakest mortar that will do the job. crete frame, as the concrete back-up a lower rate over the following years. Mortar that is too hard does not per- tends to shrink while the brick tends mit movement of adjacent brick and Another main contributor to move- to expand, a phenomenon known as can cause cracks and spalls, in which ment of brick is thermal expansion frame shortening. Composed of flexible pieces of the brick face are forced off. and contraction. Because both thermal materials, expansion joints can close Different joint types provide different and moisture volume changes are and stretch as building components weathering capabilities, with concave, related to the height of the wall as- shrink or expand.