THE MASONRY EDGE

FLASHING... Tying the loose endsINTRODUCTION

Masonry has proven itself to be one of themost durable building materials available.Three common types of masonry wallsystems are cavity walls, veneer walls,and composite (barrier) walls. The mainissue when designing a quality wallsystem is controlling water that penetratesthe wall system. A successful systemuses flashing to perform two functions: toprevent water penetration at copings andbelow openings, and to direct any waterthat has penetrated the wall back to theoutside above openings and at the wallbase. The flashing strategies herein aretried and true techniques which can helpcreate a long lasting, durable masonry wallsystem.

METHODS OF INSTALLATION

The proper detailing and installation offlashing is critical. A masonry wall’slongevity can be drastically compromisedif standard methods and procedures arenot applied. Unconventional flashingmethods, teamed with a designer’s over-sight, can produce detrimental results,such as: efflorescence, mortar deteriora-tion, spalling brick, excessive wall move-ment and interior moisture damage.

LOCATIONS

After a complete examination of the wall system, adesigner might consider flashing in numerous areas.Five of the most common areas are:

1. Above wall openings.

2. Below wall openings. (window sills, etc)

3. On shelf angles.

4. At the wall base, or where the wallstructure rests upon the foundation.

5. At the top of the wall / parapet.

The arrow indicates a properly installed, exposedmetal drip, hardly noticeable from a few feet away.

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If not properly flashed, all masonry wallopenings possess a potential moistureproblem. In brick veneer systems there

are two distinct methods for properlyinstalling the flashing membrane, asshown in Figures 1 & 2. In Figure 1the flashing membrane* is turnedup at the ends and placed insidethe head joint, forming a dam.This acts as a directional aid,

guiding water through the weepholes to the exterior surface of

the wall. In Figure 2 a self adhe-sive preformed end dam is placedunder the flashing membrane.(shown on top of flashing in thedrawing for clarity). Figures 3 & 4 showthe complex detail required to properlyflash a brick veneer bay window.Preformed end dams are used in a stair-

step fashion, culminating with aflashing tray and weep hole to

direct collected water outof harms way.

Preformed self-adhesive corners

are also avail-able for base-flashing asshown inFigure 5.

Installation OverWall Openings

FIG. 1

FIG. 2

FIG. 3

* To select the proper flashing material, consult BIA Technical note #7 Rev. February, 1985

FIG. 5

FIG. 4

Preformed insideand outside

corners

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Installation Over Wall OpeningsThe installation of the flashing for a sill conditionis similar in both cavity and veneer wall systems.See Figure 6 & 7. An end dam is used once

again to act as a moisture deterrent. Theflashing collects any entrant water, andthe end dam ensures that the water willbe directed to the exterior. Weepholes are installed to provide anavenue of egress for the moisture.Ideally the end dam would be placed

6” to 8” beyond jamb lines above allwall openings.

On Shelf AnglesShelf angles create a continuous hori-zontal break within the cavity, obstructingthe vertical flow of moisture through the airspace. If special attention is not given to thedetailing and installation of shelf angles, mois-ture infiltration, efflorescence and brick spallingcan occur. See Figure 8a. Due to the abovefactors, specifying the minimum amount of shelfangles will reduce the possibility of moisturedamage.If possible, an alternative method of design is toeliminate all shelf angles at all floor lines andbear the exterior wythe of masonry on the foun-dation as shown in Figure 8b. This eliminatespotential problems inherent in shelf angledesign. This wythe of masonry can supportits own weight for several stories, while wallties provide lateral stability.Another strategy is to bear the exteriorwythe directly on the floor slab. See Figure9. However, thermal bridging makes thistype of system less energy efficient, andmore reinforcement may be required in theslab to support the wall. Also, exposed slabsare susceptible to moisture infiltration, sospecial details must be developed to preventwind driven rain from penetrating beneath theflashing and into the building. Flashing must beset in a continuous bed of mastic, or a selfadhering flashing must be used to prevent thewind driven rain from entering beneath theflashing.

Below Wall Openings& On Shelf Angles

FIG. 9

FIG. 6

FIG. 7

FIG. 8a

FIG. 8b3

Installation at Wall Base

Installation at Wall BaseMoisture which does penetrate the wall, gradually travelsdownward. This makes the base the most vulnerablelocation for moisture accumulation. A continuousflashing must be properly installed above grade. Variousmethods of installation for both veneer and cavity wall

systems are shown in Figures 10 & 11. Properweeping to provide moisture drainage is crucial.

Weep holes MUST be used wherever flashing islocated. They must be placed directly on theflashing, and spaced no further than 24” oncenter. Weep holes can be created in severalways. Some of the most common methodsare: leaving head joints open, use of remov-able oiled rods, and installing plastic or metalvents (not tubes), in lieu of mortar in headjoint. Cotton sash cords placed 16” O.C. willalso serve as an excellent weep. There is no

universal method. Different situations willrequire different methods. The specific type of

weep hole is not critical as long as weep holesare properly installed at required locations in the

proper spacing, .

Keeping Cavity Walls CleanA cavity wall is a drainage-type wall system. In adrainage wall, some water will penetrate the exteriorwythe of masonry. The water then flows down the insideface of the masonry, is collected by properly installedflashing, and exits the wall through weep holes.Typically, the effective drainage space, or air spacevaries from system to system. The space should be 1”

for veneer work and cavity walls with closed cellinsulation, and 2” for veneer on steel studs, or

cavity walls without insulation. For properdrainage, it is important that this air

space is free of mortar droppings,which can trap water within the wall

system where it can causedamage. It requires a greatamount of effort for the mason tokeep mortar from dropping downinto the cavity. Various tech-niques such as beveling themortar bed away from the cavityand drawing a piece of wood upthe cavity to collect mortar drop-pings can help keep the cavityclean. One recent innovation is

the utilization of an insulateddrainage board. (Figure 12) This

system provides a narrower wall withan unobstructed drainage path, elimi-

nating the need for a clean airspace.

DISCLAIMER NOTICEThis guide contains technical information onmasonry wall systems. It provides some of thebasic information required to properly designand detail these systems. This booklet doesnot cover all designs or conditions. The infor-mation presented illustrates only the principlesthat are involved.

The information contained in this booklet isbased on the available data and experience ofthe technical staff of the Masonry AdvisoryCouncil. This information should be recognizedas suggestions which, if followed with goodjudgement, should produce positive results.

Final decisions on the use of information,details and materials as discussed in thisbooklet are not within the purview of theMasonry Advisory Council, and must rest withthe project designer, owner, or both.

Copyright© 1996. Masonry AdvisoryCouncil. All rights reserved including rights ofreproduction and use in any form or by means,including the making of copies by any photoprocess, or by any electronic or mechanicaldevice, printed, written, or oral, or recording forsound or visual reproduction or for use in anyknowledge or retrieval system or device, unlesspermission in writing is obtained from the copy-right proprietors.

Masonry Advisory Council1480 Renaissance Drive, Suite 401,

Park Ridge, Il 60068Phone: (847)297-6704 Fax: (847)297-8373

FIG. 11

FIG. 10

FIG. 12

Wall type Air space Veneer 1”

(wood frame)Veneer 2”

(steel frame)

Cavity Wall 1”(with rigid insulation)

Cavity Wall 2”(with no insulation)

Cavity Wall with insulation & 0 to3/8”drainage panel

Glazed brick veneer* 2”

*When using glazed brick veneer, providevents at top & bottom of wall

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