I was driving by this restaurant remodel the other day and slammed on my brakes!
I made friends with the Project Manager and he allowed me full access to the site. The first and most immediate failure you see is that the parapet walls & caps had huge failures. I climbed up to the roof for a better look. Luckily, the demo crew wasn't quite finished so I got to see some of the layers behind the stucco. The flat tops of the parapet walls had stucco on them. Stucco is basically a porous cement product so any water that hits stucco will get through to the layers behind in no time. These flat tops had 2 layers of tar paper behind them with little effort paid to sealing the joints and horizontal/vertical connections. OUCH.
These rotted parapet caps present three lessons.
Lesson #1 Don't stucco over a Parapet Cap. Stucco is porous and any water that sits on the stucco WILL get through. Parapet caps should have some type of waterproof cap to prevent water from sitting on this horizontal area and leaking behind the WRB (weather resistive barrier).
Lesson #2 If you MUST do a stucco cap then you'd better waterproof behind the stucco. Tar paper is not a waterproofing product. It does resist water, but it's not waterproof. It's paper that's been impregnated with tar. Paper is not waterproof. Tar impregnated paper is also not waterproof.
The last photo above is particularly interesting. You see that sprinkler head in the foreground? That's the only pipe or penetration I could find anywhere near this massive wall rot area. There was no rot above 4' so the leak wasn't coming from above. Remember that this building is only 10 years old. I think this is a perfect example of why I think Tar paper is a terrible product to use for a WRB. That sprinkler was wetting the wall 2-3x per week at 4 AM and no one realized it. The porous stucco soaked up the water, the tar paper got soaked and eventually the sheathing behind got wet. There was no opportunity for this wall to do to the inside our outside with that volume of water. ( See this video I made about a stone veneer failure to learn more about Reservoir Claddings including Stucco and Vapor Drive.)
Lesson #3 Plywood rocks. I realize these photos are pretty horrific, but if this sheathing would have been OSB I think this failure would have been even worse. The plywood and 2x walls were able to soak up a ton of water and eventually rot happened. However, if these leaks would have been smaller I think the real plywood and 2x's would have been able to soak up the moisture and slow dry without incident. Also, in all these photos I never saw any mold growth. Mold loves the most broken down forms of wood. Mold loves paper & OSB, but it has a harder time harnessing the food in solid lumber or plywood.
Stay tuned for a post later this week on Stucco Best Practices and how you can prevent these failures. I'm building a house right now with stucco parapet caps and I'll show you the details to do this assembly the right way!
Risinger Homes is a custom builder and whole house remodeling contractor that specializes in Architect driven and fine craftsmanship work. We utilize an in-house carpentry staff and the latest building science research to build dramatically more efficient, healthy and durable homes.