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San Jose Stucco Installation Advice to Prevent Wall Rot: Part 1

San Jose Stucco Installation Advice to Prevent Wall Rot: Part 1

One of the reasons people may avoid stucco installation in San Jose is reports of stucco-clad homes suffering from wall rot. Scientists are still wondering what exactly leads to the problem. What’s clear, however, is that the walls suffered from water damage for an extensive period of time.  

Does your stucco-coated home suffer from a wall rot? Here are the possible reasons: 

  1. Your house has OSB sheathing. This type of engineered board is prone to rot than plywood. 
  2. Your builder installed just a single layer of asphalt felt or grade D paper under the stucco. 
  3. The building paper was installed poorly. For example, failure to secure a gap between the stucco and the sheathing leads to lack of ventilation. 
  4. You have plastic vapor barrier in your wall. Condensation may build up on the barrier and cause wall rot. 
  5. The humidity in your house is high, and you have a poorly installed air barrier. 

 Do you still want to install stucco on your wood-framed wall? If you’re afraid to deal with wood rot that can happen with bad stucco installation or simply bad construction in general, then you should continue reading.  

 Rotting walls in homes with stucco installed over wood framing are a common problem in the United States. I have seen so many stucco-clad homes with decaying walls. These are not old homes. They are relatively new homes. Are builders failing to follow standard construction methods to prevent premature decaying of walls? I don’t think so. Builders, at least the licensed ones, receive complete education and training. So something else is at play here. 

 When half of the homes with stucco walls are suffering from rotting wood, stucco installation then receives a bad rep. It is a problem in Minnesota, and according to Ron Glubka, wet walls are a big construction defect in local history. The chief building official in Woodbury also noted that the building department has issued wall repair work permits for half of 670 homes constructed with stucco walls in the 1990s. We’re not talking about minor repairs. We’ve read reports of insurance companies paying more than $170,000 for stucco wall repairs, and that’s just about a quarter of the worst wall repair jobs in Minnesota.   

 But builders screw up the repair job! 

 If you thought the repairs had fixed rotting walls, you would be disappointed to know that repairs didn’t fix the problem. Some of those houses in Minnesota whose walls were repaired suffered problems. I saw several photos, and I’ve even visited houses of some of the so-called “failed rebuilds,” and I saw the reason the repair jobs failed. They rebuilt the walls by doing exactly what failed in the first place. Some rebuilds are even haphazardly done. I’ve seen taped window fins without pan flashing!  

 You can ask building diagnosticians about why fixing rotting stucco walls doesn’t work, and they will most likely tell you the reason: builders fail to address the culprits. Without an appropriate inspection, it’s impossible to catch the exact cause of wall rot. Repairmen may suspect anything without making a thorough examination; thus, important but often inconspicuous causes are ruled out. One of the culprits that are hard to notice is high indoor humidity. Poor ventilation and high humidity make walls damp.  

 It’s happening across the country. 

Rotting wood in stucco walls is a problem everywhere in the country, and we’re seeing it usually in stucco walls with water resistant building paper, oriented strand board (OSB), and polyethylene. You can reduce the risk of wall rot by using two layers of water resistant paper and using plywood instead of OSB. You can also keep moisture from the dry wood by eliminating polyethylene barrier. However, none of these techniques guarantees zero damage. 

So how can I keep my stucco wall from decaying from within?

Tip #1: Install two or more layers of building wrap. 

Okay, we now are swamped with enough proof that one layer of Grade D building paper or asphalt felt isn’t enough to protect the wood underneath from succumbing to moisture. Building codes already require a water-resistive and vapor-permeable barrier that performs just as good as, if not better than, two layers of Grade D building paper.  

Tip #2: Install ventilated rainscreen cladding. 

The common practice in San Jose stucco installation includes two layers of asphalt felt or Grade D paper, which are thought to create a drainage gap between the layers. In theory, the wet stucco applied onto the metal lathing souses the outer layer of paper. The paper wrinkles, and it stays wrinkled when it dries. The wrinkles purportedly create the gap.  

However, the theory doesn’t work in real-life situations. The incredible number of stucco-clad homes with rotting wood frames is a testament to the ineffectiveness of the theory. The wrinkles don’t prevent moisture from invading the OSB. Stucco loves water. When it rains, it absorbs water. Worse, it dries quite slowly.  

It seems that water resistant building paper isn’t doing what it’s supposed to do. Thus, we need a rain-screen gap that actually works.   

In the next article, we will introduce you to the true rain-screen gap that should keep water from getting into the wood frame.  

We at Stucco San Jose & Plastering follow the best practices in stucco installation that are guaranteed to last for a long time. If you need residential stucco repair in San Jose, call us at 408-290-1546.  

San Jose Stucco Installation Advice to Prevent Wall Rot: Part 2

In the previous article, we discussed how prevalent wall rot is in stucco homes. We also tackled the common reasons wood frames underneath stucco decays. Now, let’s talk about how you can prevent your OSB sheathing or plywood from getting wet and then turning into a rotten mess.  

Your stucco installer in San Jose should make sure that that gap about 3/8 inch thick exists between the OSB or plywood and the stucco. But that’s just the minor detail of the ventilated rain-screen gap between the stucco and the wood frame. A good rain-screen gap doesn’t just consist of two water resistive building papers, which are way deficient.  

Anatomy of a True Rain-screen Gap

First, you need a housewrap or Grade D building paper. Yes, you start with it because that’s your water-resistive barrier. Your builder should install it over the OSB sheathing or plywood. The next layer is the three-dimensional plastic drainage mat over the initial barrier. If you’re doing the job yourself, consider products like WaterWay rain-screen drainage mat or Mortairvent mortar deflection and ventilation system. Then put another layer of Grade D paper or ashphalt felt, after which you install a fiberglass lath or galvanized lath. All together, these comprise an effective rain screen.  

For those installing stucco over foam, the ventilated rain-screen gap may have to be a bit different. You need to secure vertical strapping before attaching the paper-backed metal lath. Once both are securely attached, you may proceed with stucco installation. As you don’t want to run into issues with your local building inspector, especially with details as trivial as the number and sizes of screws used for your 1×3 or 1×4 strapping, you can ask an engineer to go over the details. You can also give us a call. Your local building department shouldn’t have any objections as long as it sees your engineer’s stamp. 

Keeping Moisture at Bay

Moisture that gets into the wall is always a bad thing. It invites mold and pests that destroy your wall. If there’s wood there, you’ll soon find out that you need an expensive home repair. It’s true not just for stucco-clad homes. All houses need suitable flashing and moisture management features, but builders sometimes fail to install them — and if they do install them, they don’t install them properly. In addition, homeowners may not notice the problem, especially when other features of the house hide the problem. For instance, houses with overhanging roof edges are so well protected from rain that they don’t suffer from inadequate flashing, at least not after a major thunderstorm.  

Houses with poor roof overhangs and exterior walls made of stucco or other moisture absorbing materials are not going to fare well, especially when the rainy months set in. But aren’t walls supposed to protect your house from the weather. For the most part, yes, but any type of wall can have a problem with rain. Water can seep into wood, brick, stucco, or vinyl sidings. It’s not just the material. The joints and connections serve as entry points for water. Wind-driven rain makes things worse.  

Also, it doesn’t matter what material you use. At some point, water gets into the wood and causes it to grow mold and then rot. Even steel rusts when exposed to water. Tight construction is ideal. However, construction has become more of a business than an engineering feat. Builders are racing to gain more clients and getting in cash, leaving homes with defective walls. We’re not just talking about stucco-clad homes here.  

In the case of stucco walls, a rain screen is almost always necessary. But a vented rain screen is expensive and unconventional. You will find very few stucco contractors in San Jose who implement proper rain screen installation. For instance, flashing must be installed carefully under the housewrap. Roof overhangs should be extended to cover as much of the outer wall as possible. These are just some of the things to take into consideration, and even the minor details require labor and materials. Some contractors find such tasks so trivial that they don’t bother adding those little details.  

Proper Grading Around Your House

The ground should slope downwards away from the house. The slope keeps water from pooling around the house and possibly flooding your basement on a rainy day. However, we’ve seen people overdo this. This is terrible for homes with stucco walls. Because stucco looks like cement, people think it’s okay to raise the grade around the house well above the wood framing. So when it rains, the surrounding soil gets wet. The stucco gets wet, too, and because it absorbs water, the OSB sheathing gets drenched as well. You can verify with home inspectors to ask how common this problem is.  

Modern Stucco Walls

Some contractors suggest one-coat stucco, a shift from the traditional three-coat stucco, to avoid wall rot. Also called exterior insulation and finish system (EIFS), one-coat stucco involves a layer of Portland cement. A thin layer of finish coat is laid over it. The formulation includes polypropylene fibers and polymers. Installers find the single coating convenient. They only have to install a rigid foam, a plastic mesh over the foam, and then stucco over the foam.  

However, some inspectors still discover wall rot in EIFS. This setback prompted the EIFS industry to modify installation details to include a drainage layer between the foam and the OSB or plywood. This modification seemed to minimize wall rot issues.  

What we’re learning here is that lack of drainage gap between the stucco and the wood framing or OSB sheathing is the primary cause of wall rot, regardless of the type of stucco installation.  

Do you have questions regarding stucco? Call us at 408-290-1546. 

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