Technical Notes B on Brick Construction

1 21 BREVISEDA pril2002designed to stop any mortar droppings from blocking thecavity and allow water to flow around them. Use ofdrainage materials is not required, and in some casesmay contribute to water penetration problems within thewall. More information on drainage materials is pre-sented in Technical Notes21A of this series. Drip Edge/Flashing ExtensionWater that collects on flashing can re-enter the wallbelow if flashing terminates behind the face of the best performance, flashing should be extended 1 4in.(6 mm) beyond the wall plane and turned down at anangle of 45 degrees to form a drip. This forces wateraway from the wall protruding flashing is neither possible nor desirablein some cases.

2 For example, exposure to ultraviolet radi-ation may cause some flexible flashings to these cases, flashing should be cut flush with the faceof the wall. In cases where the flashing itself cannot beexposed, a non-corrosive metal drip edge may be used,see Fig. 1. Before specifying metal drips to be used inconjunction with steel shelf angles or lintels, the poten- Brick MASONRY CAVITY WALLSDETAILINGA bstract:This Technical Notescontains recommendations for the proper detailing ofbrick masonry cavity walls. Flashing, weep holes, and sealants are prescribed to control mois-ture penetration. Bond breaks, adequate bearing details, expansion and movement joints areshown.

3 Seismic detailing is also Words: bearing, cavity wall, expansion joints, flashing, sealants, parapets, and workmanship alone are not sufficient toensure adequate cavity wall performance. Unless prop-erly detailed, cavity walls constructed of the finest mate-rials by the most talented masons will suffer the conse-quences of poor detailing. This Technical Notespro-motes quality cavity walls by discussing and depictingpertinent is the third in a series of Technical Notesdevot-ed to Brick masonry cavity walls. Other Technical Notesin this series discuss cavity walls in general, including;properties, design, material selection, and Technical Notesaddresses proper detailing forbrick cavity AND WEEP HOLEST hrough-wall flashing and weep holes are installed inexterior masonry wall Construction to collect and divertmoisture that penetrates the exterior wythe of masonryto the outside of the wall.

4 Through-wall flashing mustbe provided at the base of the wall, at roof and chimneyintersections, at roof and wall intersections, and at thetop of parapets. Flashing is also needed over and underdoor and window openings, at shelf angles, and at otherhorizontal discontinuities in the cavity. Any penetrationsin the flashing membrane should be sealed to preventleakage. Sealants and flashing used together must becompatible so that staining does not occur and long-termperformance is maintained. For flashing and weep holes to perform as intended,the air space separating the masonry wythes must bekept clear of mortar droppings and other obstructionsthat may bridge the air space.

5 To achieve this end, pri-mary importance should be placed on good workman-ship. A secondary method of keeping the cavity clean isthrough the use of drainage materials specificallyMETAL DRIPFLASHINGSEALANT (OPTIONAL)SEALEDLAP SPLICESEALANTF lashing with Metal Drip EdgeFIG. 1 Technical Noteson Brick ConstructionBrick Industry Association11490 Commerce Park Drive, Reston, Virginia 201912tial for galvanic action between the metals should beconsidered. Flashing materials should overlap the metaldrip edge by a minimum of 1 in. (25 mm), and be fullybonded to the top surface of the drip edge with a masticor manufacturer-approved sealant.

6 Metal drip edgesshould be sealed at all laps and HolesWeep holes should be placed immediately above allflashing and be spaced no more than 24 in. (600 mm) oncenter when open head joints are used, and no more than16 in. (400 mm) on center when wick materials or roundtubes are used, see Fig. 2. Open head joints are preferredbecause they allow water to drain more quickly. Insectsdo not commonly enter working weep holes, but theycan be prevented from entering open head joints byusing louvered, vent-type weep inserts, stainless steelwool, or other drainage Dams Detailing and installation of end dams cannot beoveremphasized.

7 Their purpose is to ensure that collect-ed water is directed toward the weep holes where flash-ing is not continuous. Such areas occur above windows,doors and other openings and under sills beneath win-dows. End dams are also used in conjunction with trayflashing at arches, when flashing is stepped, and wherea lower sloping roof line intersects a wall. Without enddams the collected water may run off the ends of theflashing into the air space and saturate the brickworkbelow. To prevent this, each end of the flashing shouldextend beyond the opening and turn up into the headjoint a minimum of 1 in. (25 mm,) or a prefabricated enddam may be used, see Fig.

8 3. Foundations To prevent moisture penetration and promote cavitydrainage, place the bottom of the wall so that flashing isabove the finished grade. Care should to taken to ensurethat flashing and weep holes are placed far enough abovegrade, typically 8 in. (200 mm), so that they will not becovered by future grading or landscaping, see Fig. 4. Withbasement Construction , it is important to use through-wallflashing at the bottom of the cavity to prevent moisturefrom penetrating to the basement wall, see Fig. 5. Belowthe flashing, any cavity should be filled solid with mortaror grout. The flashing also prevents rising damp, groundwater drawn up into the brickwork by capillary reduces the potential for staining and flashing also serves as a bond break between the brickand the concrete foundation.

9 This permits differentialmovement between the materials and reduces the likeli-hood of cracking. In Construction without basements, theflashing may also serve as a termite HEAD JOINTS@ 24" (600 MM) TUBESOR WICKS@ 16" (400 MM) of Weep HolesFIG. 2 REINFORCEDCMU LINTELCONCRETEMASONRYWYTHE(INNER WYTHE)STEEL ANGLE\LINTELTROUGH WALLFLASHINGBRICKWYTHE(OUTERWYTHE)1 MIN.(25 mm)End DamFIG. 3 ColumnsIn some cases, vertical supports may make it neces-sary to cut, puncture or otherwise interrupt the this occurs, it is important to make sure that allopenings in the flashing are tightly sealed, and that theflashing is attached to these supports with mechanicalmeans or approved adhesives.

10 A common problem con-dition exists when the inside wythe of a cavity wallspans between steel columns, and the column flanges areperpendicular to the masonry. Fig. 7 illustrates one waythat this problem can be addressed. The flashing isformed into a tray and adhered to the column. Cut brick3 CornersIt is important to make sure flashing is continuousaround corners. Forming corners with conventionalflashing is a complicated process involving foldingand/or cutting, which increases the potential for flashingfailure. Specifying prefabricated corners eliminates theneed to cut, patch and fold flashing, thereby reducingsome of the potential for water penetration, see Fig.