June, 2017
Inspection News and Views from the American Society of Home Inspectors

Stucco Revisited


Publisher’s Note: We’ve published articles about the topic of stucco in the
Reporter in the recent past, but this one, written by ASHI Past. President David Tamny, offers a unique perspective and technique that sets it apart.

The problems with exterior insulation and finish systems (EIFS) have been well documented for years. Now we know that traditional three-coat plaster stucco, one-coat stucco and cultured stone systems all have had similar problems. I used to believe that traditional three-coat stucco systems were immune from these issues, but I’ve learned through experience that this is not the case. The problem for home inspectors is that many problematic conditions are not readily discernable by visual inspection, and I would contend that it can be hard to determine the extent of these problems by using most of the noninvasive or minimally invasive methods available to inspectors.

A stucco cladding system depends on each of its component parts, which often are installed by specialists from different trades, to work together to drain water. Water, whether in the form of liquid or vapor, can be extremely destructive to homes if it is not allowed to discharge from the building envelope.

Opinions about whether the exterior cladding should function as a barrier or as a rain screen have changed over time. Building scientists, such as Joe Lstiburek of the Building Science Corporation, advocate for the rain screen, which allows water entering the system to drain out. The rationale is that barriers will fail and water eventually will penetrate the building envelope. If water doesn’t have an exit path, it will cause damage. Although sealants have a role to play, caulking the house is rarely the solution when it comes to stucco problems, but this is the most common recommendation from stucco contractors and those seeking low-cost solutions. For home inspectors who want to understand more about moisture and buildings, Joe Lstiburek’s work is mandatory reading (visit https://buildingscience.com/ for more information).

Infrared Images
Because window flashings and water-resistive barriers are not visible after the house has been completed, the inspector cannot verify whether flashings have been properly installed. The infrared camera has been promoted as an almost magical device that can help inspectors discover all manner of problems that cannot be seen with the naked eye. My experience using infrared cameras to discover conditions hidden within the wall cavity has shown me that it is a haphazard option at best. The infrared camera photographs an image that depicts the surface temperature of the wall. The theory is that evaporative cooling will cause wet surfaces to appear cooler than dry surfaces; however, objects can appear cooler for many reasons that often are unrelated to water damage. If the surface is wet enough to show up as a cool surface in an image taken by an infrared camera, the surface is also probably wet to the touch or visibly wet to the naked eye. Mold and rot, on the other hand, may be concealed within a wall cavity and may not be detectable in infrared images at all.

The notion of using a method that can find problems deep within a wall cavity without having to destructively open the wall is appealing because you don’t have to damage the interior or exterior to determine if water intrusion has occurred. However, I would never communicate to a buyer, who is relying on my opinion to decide whether to buy a home, that the home does not have hidden damage on the basis of infrared images alone.

Invasive Testing
A major hurdle to overcome when inspecting a home with stucco is obtaining permission from the seller to do invasive testing. Even if testing is only minimally invasive, it can be very difficult to repair the test areas to make them look exactly as they did before the test. Also, the seller may not want to know whether there is damage. If a prospective buyer decides not to buy the house and the seller knows that the house has stucco problems, the seller must disclose that information to the next prospective buyer or possibly spend tens of thousands of dollars to make repairs. There is little incentive, from the seller’s perspective, to allow invasive testing.

Moisture Mapping
Many inspectors use a testing methodology that had its beginnings in the EIFS failures of the 1980s. In addition to conducting a visual inspection of the critical details to ensure conformance to industry standards, the inspector could use the method of moisture mapping to determine whether there is damage behind the cladding. Moisture mapping involves taking specific moisture content readings of the wood sheathing at control locations and in areas where damage is suspected, such as beneath windows and at roof-wall connections. Then, the inspector maps the façade to show areas of probable damage. The following case study, however, calls into question whether moisture mapping is sufficient to determine whether there is hidden damage.

A Case Study
Recently, a buyer who was entering a contract to purchase a home consulted me for advice. The buyer had already received the results of a home inspection and the inspection report did not list any suspected stucco problems. The home had three-coat traditional Portland cement plaster stucco on wire lath, a single layer of 15# felt paper, functioning as the water-resistant barrier, and OSB sheathing. The home was constructed by a major homebuilder in 1999 and it met the building codes at the time. With the seller’s permission, the buyers decided to begin kitchen renovations before closing on the house.

Photos 1 and 2 show what the interior and the exterior of the home looked like at the location where the kitchen cabinets and drywall had been removed. It’s easy to see why a home inspector who performed a visual inspection of the exterior of this home would not report that the cladding was defective. The stucco was free of stains and cracks, both of which can indicate water intrusion.

When I visited the home, the stucco contractors were on site and ready to make the repairs to which the seller had agreed. The buyers wanted me to determine whether the planned repairs were sufficient and whether there was additional water damage. The seller had not given permission to conduct additional invasive tests and the closing of the home sale was scheduled for the next day.

Photo 3 shows what the exterior sheathing looked like after the stucco was removed. It was apparent, by direct observation, that the windows were not flashed properly. The original builder had installed the windows and trim around the windows without placing flashings before installing the stucco. The felt-paper, water-resistive barrier terminated below the trim and the barrier did not extend beneath the window nailing flange, as is now the proper practice. Water was collecting along the window frame, running behind the trim and entering behind the water-resistive barrier beneath the window. The damage began at the line at which the felt paper terminated.

  I tested the moisture content of the damaged wood and found it to be an acceptable 10.8% wood-moisture equivalent (WME) (Photo 4). The stucco had been removed just minutes before I did this testing, so the wood did not have an opportunity to dry out. My point is that if no one knew there was a problem and had drilled holes into the stucco to allow for the insertion of moisture meter probes, an inspector could have concluded incorrectly that there was no problem. At this location, the wood was firm, although clearly damaged by water.

The buyers’ question about this home was whether other locations also had damage. The stucco contractor, believing that stucco is a barrier system, thought that the damage was limited to this one area because the wood trim was tight at the other windows and he didn’t see any gaps that would allow water infiltration. I disagreed, based on the assumption that the original contractor would have installed all of the windows similarly and, therefore, all of these areas could have problems.

Unfortunately, this was a question that we could not answer adequately through moisture mapping unless the weather conditions had been such that the sheathing was wet or soft enough that we could detect damage by probing. In this case, it had rained approximately 1 inch during the week before this site visit. The sheathing obviously had been damaged by chronic water infiltration, but had dried sufficiently to avoid detection with moisture meters. It was not soft enough at all areas to be obvious when probing, although in this case, the area under the right side of the window was rotted enough to be detected by probing.

The upper story window had damage as well, but the area was not rotted sufficiently to be detected by probing and it was not wet (Photo 5). This is an example of why inspectors should choose carefully where to insert moisture probes, because conceivably, you could miss detecting significant damage by inches.

In lieu of cutting more stucco at every location of potential damage, a contractor could remove the drywall under each window on the interior of the home so that an inspector could assess for mold and damage within the wall cavity. Drywall removal is an invasive technique, but it is far less costly to repair and match drywall than it is to remove and replace stucco. I have found this strategy to be a straightforward way to determine quickly whether OSB sheathing has rotted. You also can determine whether there are problems related to condensation, which could be the case if the original contractor used older, polyethylene vapor barriers.

Complications and Costs
These are complicated issues for home inspectors. If a home inspector recommends performing costly, invasive inspections on every home that has stucco, that inspector will not be very popular, to say the least. But on the other hand, what inspector wants to have a client who later discovers extensive damage they “missed” during the inspection? Moisture mapping by probing the sheathing at vulnerable locations is probably one of the best methods to determine whether there is damage and this is the accepted standard for stucco testing. My point, however, is that this method is hardly foolproof and, as an example, the cost for the repairs to the limited area in the kitchen described in this case study was $12,000. The full cost of all of the repairs has yet to be determined.

David Tamny is an ASHI Certified Inspector and owner of Professional Property Inspection Consultants (http://www.worryfreeinspections.com/) in Columbus, OH. Tamny, a registered architect, was ASHI President in 2010. He has been performing home and commercial inspections since 1992.