b'WRB and exit the wall base at a weep screed or dissipate Weep Screeds are Recommendedthrough evaporation. There are limits, however, to theThe second component of the systems design requirementsvolume of water a stucco clad wall system can successfully is a weep screed at the bottom of the wall and at all soffits.handle.Wherever the vertical wall terminates and/or changesdirection, water that may collectStucco can be applied over block (typical CBS construction) behind the stucco veneer needsor over wood frame (often used for the upper story ofto be able to drain out. This neg-residential homes). In CBS construction, the block is the atively effects window and doorWater-Resistant-Barrier (WRB), and in wood frameopenings where the window unitapplications, stucco is placed over a WRB which is ais recessed from the plane of themembrane such as water-resistant building paper. wall. If no weep screed isIt is not the province of this manual to discuss variousinstalled, the water will beconstruction methods. However, the success of a windowdirected to the header of the or door installation is dependent on the successfulwindow unit, and this is oftenhandling of the water that will penetrate the stucco.the case. Therefore, water needsThese instructions are dependent on certain principlesto be directed away from theto accomplish just that. window/door header and backinto the drainage plane to beThe role of Concrete Block able to escape from the behindThe concrete block used in residential housing, whenthe veneer and not penetratecovered with stucco, becomes the water resistant barrier. into the interior of the building.What that means is that it retards the passage of the water Proper Sill Paninto the interior of the home.Many mistake that to mean, The third component of an effective stucco wall, is theno water should be absorbed into the block, when in reali- drainage of the sill ofty, the successful performance of the CBS wall depends on the window or door unit.a certain amount of absorption to handle the inevitable As the illustrationswater penetration of the stucco in severe weather. show, improper sillTwo ways water that gets behind stucco is handled shape, improper sillslope, and improper Drains toDrained Assembly drainage path for the sill Insidewill cause problems andnot allow the stuccowall to perform as it wasintended.The last consideration isMass Assembly the creation of the win-dow or door opening.Too often it is outDrains toof square, improperly Outsidesized, improperlybucked, and improperlyprepared to accept thewindow or door. Added to this is the reliance on other trades to prepare the opening before the window installer technicianarrives to fit the product.When stucco claddings leak, the penetrating water is traditionally managed in two fundamental ways. The first is These instructions will assume that the window fitter hasdirection to a water resistant barrier such as in a drained examined the opening and has assured that the rough sillassembly where the water exits the wall downward, and the is proper, and that the dimensions are accurate withinsecond is a mass assembly where the eater is absorbed in 1/8 in plumb, square and level. No fenestration productnon-water sensitive material and released to the interior should be installed in any other opening. In addition, theand exterior in a controlled way during drying periods.window fitter should fabricate and install the wood bucks,Concrete block serves this purpose well and it is expected and the sill pan or equivalent(s) and seal them adequatelyto do so in CBS construction. However, it is also expected before mounting the new window or door.that the rate of drying will not be exceeded by waterCredits: Photos and Artwork courtesy of Building Sciencecollection, so fenestration installation must limit possibility Corporation; TM Windows and Doors; Builder Magazine, Decemberof excess water getting inside the cavity. 2005; and AWDI Standards, version 1.3.Window Fitters Guide to Window Installation1262020 AWDI, LLC Do not reproduce without permission'