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Winds of change: storm damage uncovers some basic flaws in siding detailing.

THE 2004 HURRICANE season blew the cover off a weakness in the way stucco is usually installed, with a number of Central Florida homes springing leaks despite having suffered no wind damage. The problem led the Florida HBA to commission a forensic investigation of the homes in question. The investigation was led by Dr. Joseph Lstiburek, president of Building Science Corp. in Westford, Mass., and a national expert on water damage. His report outlines the sources of the leaks and suggests ways to prevent them in the future.

But stucco isn't the only siding that has been having problems. Leaks have been reported on homes with brick and stone veneer, vinyl, and other sidings. In every case, the underlying cause is similar: an assumption on the part of designers, builders, and installers that siding makes a house watertight. Not so, say the experts. "All sidings leak," says Steve Easley, a Danville, Calif.-based principal at Building Media who helps builders solve building science and moisture-related problems. "Walls have to be able to drain, and they have to be able to dry. The only way to make sure that happens is to make the building tight before the siding goes on and to give any water that gets past the siding a way to get out."


That was certainly the case with the Florida homes. Lstiburek's report points out that stucco is designed to naturally absorb moisture during a rainstorm, then gradually shed it into the atmosphere during dry periods. But in Florida, multiple storms with unprecedented amounts of rain overwhelmed the stucco's ability to hold moisture, causing it to shed excess water to the inside of the homes. The report suggests changes to wall assemblies and coatings that could limit or prevent such damage should a similar sequence of storms take place.

One change concerns secondary water barriers. Stucco is generally applied over a barrier layer of felt paper or building wrap. While one layer will keep the wall dry under normal conditions, if a barrier stays wet long enough (as was the case during the Florida hurricanes), moisture may eventually wick through it to the sheathing. Lstiburek's report advises installers to create a capillary water break by putting stucco over two layers of building paper or a layer of building paper and a layer of plastic housewrap.

Others recommend going further. Easley says you will get even more protection by using two different types of barrier: a layer of drainage wrap that's placed against the sheathing, then topped with a layer of felt or standard building wrap. The crinkles in the drainage wrap create small airspaces between the two layers, which serve the same purpose as the drainage plane behind brick veneer.

Most codes already require installers to use double barriers over wood sheathing. (The Florida homes were built with concrete block walls.) In California, it's common practice on all homes, regardless of sheathing type, according to Ron Webber, principal of Pro Coat Systems in Escondido, Calif., a stucco contractor with 30 years of experience who also acts as a consultant to builders. "The code only requires a m-minute weather barrier, but that is insufficient," says Webber. "Most good installers will create a 60-minute barrier, which means using two layers of Tyvek or other combinations of water barrier materials."

Water barriers are only half of the story, however. Webber has conducted thousands of water tests on stucco as part of his consulting practice. "Ninety percent of all intrusions occur where the stucco ends at doors, windows, and penetrations such as electrical boxes or vents," says Webber. These problems are making news in other parts of the country: a class action lawsuit by owners of Del Webb homes in Las Vegas charges that water damage was caused by the lack of weep screeds at the base of stucco wails, leading to cracked stucco, mold, and fungus growth. (See "Waterlogged," July, page 48.)

Lstiburek's report recognizes these problems as well. It recommends that installation details be developed that will better prevent water from leaking in and around doors and windows than standard practice, and that these new details be added to the Florida building code.


Stucco isn't the only material under scrutiny Growing water intrusion problems are leading to tougher installation requirements for all siding types. The 2006 version of the International Residential Code will require a secondary moisture barrier behind all sidings. But as with stucco, potential problems lie in other installation details. Easley reports that much of the water damage he sees is caused by sloppy installation and that builders may have to inspect their installers' work more closely Here are some things to look for on different types of siding.

Brick and Stone Veneer. Most problems with brick and stone are caused by clogged drainage planes. "The most common mistake I see is that installers slop a lot of mortar behind the brick, which ends up being a bridge that wicks moisture into the wall," says Easley The slop can also clog the weep holes at the base of the wall that are supposed to let trapped water drain out.

On brick siding, codes require weep holes every 24 inches along the bottom of the wall. Easley recommends putting a weep hole after every other brick, both at the base of the wall and over doors and windows. Weep holes need to be above grade. "Many times an installer will put weep holes at the brick ledge, then the landscaper will back fill over them," Easley says.

One traditional procedure is to put natural fiber rope in the weep holes. The rope will let water wick through to the outside but will also prevent the hole from filling with mortar during installation. And over time, the rope will eventually rot out, leaving a standard weep hole.

Synthetic mesh products, such as Mortar Net by Mortar Net USA, based in Gary; Ind., can be put inside the base of the wall to prevent small amounts of mortar slop from blocking lower weep holes.

Vinyl Siding. Vinyl siding has weep holes built into it. They are there for a good reason: Vinyl leaks, something a lot of installers don't consider, according to Easley. The most common mistake he sees is the lack of a good moisture barrier behind the siding. "Since vinyl siding leaks, why wouldn't you have a moisture barrier?" he asks. He says it's important to tape the joints on the building wrap and to make sure all penetrations are flashed and sealed before the vinyl goes on.

Other vinyl siding mistakes include improper detailing at joints, particularly where sections of J-channels meet around windows. But if a building is made tight before the vinyl goes on, it will rarely have problems. If the installer does no more than put J-mold on and try to seal it with caulk, water can easily be funneled into the window's nail fin.

Cultured Stone. Cultured stone has more in common with stucco than with stone. It is mortared to the wall without an airspace, and air pockets created in the material during manufacturing can make it porous. In addition, cultured stone has ledges that don't drain well. The fix is also the same as with stucco: a layer of drainage wrap followed by a layer of building wrap or building paper.

RELATED ARTICLE: Stucco's dirty secret.

Low-quality sand can guarantee long-term leaks.

Stucco is a mixture of sand, cementitious material, and water. How pure the sand is will have a long-term effect on how well the stucco manages water. Ron Webber, a stucco contractor and consultant and principal of Pro Coat Systems, says that the sand used on a lot of homes is dirty enough that the stucco can't do its job.

Webber says to ask for sand that has been through an ASTM D2419 test, which measures the amount of clay and silt it contains. High levels of clay and silt will make the stucco easier to spread, according to Webber, "but you will need more water to achieve the recommended slump. This water will evaporate out of the mixture when curing, leaving more air pockets in the stucco." These air pockets become tunnels that make it easier for water to work its way to the siding.

If ASTM test results are not available, Webber says that a simple alternative is a glass jar test he learned about in a 1937 stucco "bible" by Byron Dalton:

"Fill a one-quart mason jar halfway with sand, then fill it the rest of the way with water, screw on the top, and shake it up," Webber says. After 30 minutes, the larger aggregate will have settled to the bottom, and fine clay and silt will be on top of it. "Too many fines are not good. A high-quality sand will have about .25 inches of silt on top of 2.5 inches of aggregate," Webber says. Webber recently used Dalton's test on four random batches of sand. The worst quality sand required twice as much water as the best.
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Author:Wardell, Charles
Geographic Code:1U5FL
Date:Dec 1, 2005
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