Some parts of the country have been seeing problems with stucco-sided houses thrown up by developers during the housing boom. One remodeler in southeastern Pennsylvania has been hired to fix damaged homes that are as young as five years old. The symptoms were leaky doors and windows, and when he stripped the stucco he found considerable rot in the sheathing and framing around those windows.
In most cases, the culprit behind these problems is poorly detailed or inadequate flashing around windows and doors and along the edges of walls. At that Pennsylvania house, the windows had merely been set in the openings and taped to the sheathing. Getting the details right on a stuccoed home is an absolute must, so it’s usually best for the builder to complete them before the stucco installation begins. The builder also should oversee the stucco installation.
Here are the key details that deserve scrutiny.
One sign of a sloppy job is stucco applied tight against windows or doors, an indication that no casing bead has been installed. (See illustration.) Casing bead is crucial: It creates an expansion gap that lets the framing and sheathing expand and contract without cracking the stucco or the windows.
Lack of a casing bead is especially bad on a new home. As the framing lumber dries and shrinks, it can put a lot of stress on vinyl window frames and can even crack the window’s welded joints, opening a path for water to get into the wall.
There are two ways to detail a casing bead: With vinyl J-channel or with a product called E-Z Bead made just for this purpose. In both cases, the bead is separated from the casing by a 3/8-inch space that gets filled with a rubberized caulk applied over a flexible base. E-Z Bead has a built-in foam extrusion that serves as that base, while J-channel requires the use of foam backer rod.
It goes without saying that windows should be carefully flashed, but often they aren’t. They should also be detailed so that if they do leak, water can flow back outside. A good flashing job will have several overlapping layers. The sequence for applying those layers is as follows:
Bevel the sill. Though not often done, this is a worthwhile precaution. Before installing the 2x4 rough opening sill, run it through a table saw to create a 5-degree slope. That way, any water that makes it to the sill can more easily flow out through the bottom of the window.
Install the bottom spline. Fasten a strip of housewrap to the sheathing at the base of the window, cutting it in a U shape so that the ends extend a few inches up the sides of the window.
Tape the sill. Apply flashing tape to the sides and bottom of the window opening. The tape should cover the sill and extend 6 inches up the face of each jack stud. Fold the excess down over the strip of housewrap at the base of the opening.
Install side splines. Staple 18-inch-wide strips of housewrap to the 3 1/2-inch faces of the jack studs, and fold the excess over the sheathing, to act as splines. The stucco contractor can then tuck his stucco wrap under these splines as well as the spline at the base of the window.
Set the window. Set the window in the opening, bedding the flanges in sealant.
Tape the flanges. Put another layer of tape over the top and side flanges of the installed window.
Install head flashing. If the job calls for it, install head flashing at the top of the window.
The edges of walls also need attention. On homes with vented soffits, wind-driven rain has been known to blow up into the vents, then seep down behind the drainage plane. A good precaution is to install 18-inch strips of specialized stucco wrap at the top of each wall before putting the soffits on. (In a remodel, it can be worth the time to remove and reinstall the soffits). It’s also a good idea to put strips of stucco wrap behind rake boards on gable ends. These strips need to be wide enough that there is plenty of extra paper hanging down past the base of the finished soffits.
One common mistake is to put stucco directly over the stucco wrap. The problem is that the wrap has a grooved surface designed to serve as a drainage plane; applying stucco directly over it fills the grooves and defeats its ability to drain water. The correct approach is to put Grade D felt paper and metal lath over the wrap, then apply the three-coat stucco finish. This system provides a good bonding surface for the stucco and allows drainage.
The stucco wrap should be carefully tucked behind all the strips of housewrap around windows and doors, as well as at rakes and soffits. It should be lapped over the drip cap at the tops of windows and doors. All joints should be taped to seal out drafts. Make sure the stucco contractor installs weep screed—a metal flashing that’s placed at the base of a stucco wall to provide an exit path for any water that makes its way past the stucco to the drainage plane. Where a deck is flashed to the house, the weep screed goes over the top of the Z flashing and beneath the stucco wrap.
Getting good results on a stucco installation requires hands-on management by the builder. The builder and stucco contractor should review every detail beforehand, and agree on who is responsible for what. The builder or the builder’s job supervisor should be on site during critical phases such as the lapping and tucking of the paper, in order to ensure the details are done right.