Got Mold?

Choosing the right exterior details and installation techniques to avoid moisture and mold problems has become a science. Take control and reduce your risks with these first steps.

Source: TOOLS OF THE TRADE Magazine
Publication date: 2004-09-08

By By Mark Clement, Illustrations by Harry Whitver and Evan P

While mold often appears in buildings as a musty smell, it might as well show up wearing a lawsuit. According to the Insurance Information Institute, in 2002 U.S. insurers paid $3 billion in mold-related claims -- more than double the $1.3 billion figure in 2001. Forty state insurance departments have approved mold exclusions and/or limitations on homeowners' insurance policies. Before 2000, the few mold-related claims that occurred generally ranged between $3,000 and $4,000. Today, claims average between $15,000 and $30,000 and can exceed $100,000 each. Commercial claims can reach into the millions.

If your customer finds stained drywall or disintegrating siding and sheathing because of a plumbing leak or poorly detailed window flashing, guess whose phone will ring first? Complicating this is that some lawyers tack mold-related problems onto other construction defects claims, even when there is no evidence of mold, says attorney Russ Nassof, a principal at Environomics, a national environmental investigation company based in Bethesda, Md. This would be less worrisome if insurance underwriters were standing behind their contractor-customers in the face of moisture and mold-related claims, but they're not, so you're likely to be fighting these battles alone. According to Nassof, insurers are looking for ways to protect their own businesses and cover contractors simultaneously. One way they're trying to cover customers is by certifying training programs.

To protect yourself, you must act now. Step 1: Build a strong first line of defense against moisture intrusion into the building envelope. Learn as much as possible about the latest details and proper installation techniques for exterior systems, including sheathing, siding, windows, housewrap, and flashing. Step 2: Learn to build a second line of defense called a "drainage plane," and realize that drainage planes need to be different depending on each construction system and climate. Step 3: Determine what type of vapor barrier is best for your climate and where it needs to be installed.

The idea of prevention is easy to get your head around -- keep the water out -- but implementing sound practices may require re-evaluation of how you detail. And, there's one more thing to remember: No matter how hard you try to keep water out, it will probably get in anyway.

This is where a new specialty -- building science -- is playing a larger role on the jobsite than ever. Building scientists have concluded something many builders thought otherwise: Buildings -- no matter how conscientiously sided, papered, flashed, and caulked -- leak water. They always have, and they always will. But it's a more dangerous dilemma than it used to be because we demand more from a home than ever.

Wood frame wall with OSB and housewarp; modified "I" cut in housewrap

Older buildings that leaked have proven no real problem, historically, because those buildings also leaked air. For example, they had less insulation than today's homes or were sheathed with 1-by (skip-sheathing), which allowed air to circulate through stud cavities, drying them out. Since mold requires three things to exist -- a food source, warm temperatures, and moisture -- removing moisture from the picture effectively starves it to death. Houses, obviously, are tighter now and more thermally efficient than ever, which means far less air passes through the wall cavity. And, we're packing them with modern building materials that also provide a greater abundance of food for mold spores, such as organic paper-faced drywall instead of cementitious plaster. These materials, combined with heat flow reduction in tighter houses, changes the drying rates of buildings, according to Mark LaLiberte, a building scientist with Building Knowledge in Minneapolis. So, we're packing our buildings with more free food for the mold, then locking the doors until the smorgasbord is over.

Experts indicate that there are three distinct reasons buildings fail nationwide: lack of a proper drainage plane, improper placement and location of a vapor barrier, and trapping moisture in walls by using soaked materials.

Drainage Plane. Creating a proper drainage plane is the key element in managing moisture. And while most builders might mistake weatherboarding (or lapping) housewrap behind exterior cladding as a sufficient backup in case moisture gets past the flashing and siding, it's more involved than that. First, you've got to assume that moisture will get past exterior finishes. This means "designing a wall section that enables all nine parts of the section -- exterior paint, cladding, paper/wrap, sheathing, framing, vapor retarder, drywall, drywall mud, and interior finish -- to work together," says Peter Yost, a former builder and currently a researcher at The Building Science Corp. in Westford, Mass. "We have higher-performance wall systems than ever, but they're more complex and finicky. Part of the problem is that while building materials change constantly -- we don't. Builders must evolve their techniques to keep pace."

Because the key to understanding moisture control is twofold (first, you must keep the moisture out; second, you must evacuate the moisture that gets in anyway), the drainage plane is as important as cladding in defending against mold-related callbacks. A proper drainage plane creates a gap between the exterior cladding and the wall sheathing. An extreme example is vertical strapping nailed under horizontal lap siding. That gap allows water to course down, out, and away from the building envelope before it does damage; it also enables air to circulate. A proper drainage plane also means properly and thoroughly detailing every building penetration, even light fixtures, electrical boxes, and dryer vents. Despite what many crews do, caulk is simply not enough to do this. But how you detail your wall sections depends on where you build–climate impacts protocol, so check out "Resources for Success" for climate-specific information.

Housewrap folded in; head alternatively tucked under; install wood backdam

Vapor Barrier. The vapor barrier problem is often the question of whether and where to put a vapor barrier on the wall. So first, throw out all old assumptions about vapor barriers; it's time to update your approach. For example, facing studs with polyethylene is common practice for builders using gypsum sheathing, but the "Mold & Moisture Intrusion Case Study Report" prepared for the National Center for Housing and the Environment in Washington, D.C., by the NAHB Research Center states: "In some structures located in a mixed cooling and heating environment, a polyethylene vapor retarder installed on the interior face of the framing may be improperly placed on the cool surface, which can result in a moisture buildup in the wall cavity. The use of Kraft paper-faced insulation may be advisable in lieu of polyethylene to prevent this."

The report also cites numerous case studies of improperly installed vapor barriers where the sites were inspected, but there were no building code violations. Codes haven't caught up with many modern building practices for mold prevention, indicating that builders must rely on their own initiative to research best practices and manage moisture movement through a building. While locating the barrier and specifying the type is a complex -- and critical -- decision, there may be a simpler solution. "Because moisture moves from warm to cold (toward air-conditioned spaces in summer; toward cold exterior air in winter), we do not recommend a traditional plastic (or impermeable) interior vapor barrier in all but the coldest climates," says LaLiberte. "However, there are semi-permeable vapor barriers that may be appropriate for your climate and building system." While this isn't a cure-all (keep in mind you still need an exterior barrier), it can eliminate variables at a place where many buildings fail. "The goal is to build forgiving buildings, buildings that react to events in their life cycles," says LaLiberte. "In other words, buildings that get the opportunity to dry out if they get wet."

But walls aren't the only place requiring vapor protection. Contractor Bob Rudd, who owns Rudd Inspections and Environmental Services, is principal at the Construction and Environmental Training Institute International, both in Las Vegas, and works with builders investigating moisture incursions, developing prevention protocols, and consulting on remediation techniques, cites that slabs and crawl spaces are huge sources of water vapor that penetrates the living space. If the concrete guys fail to install the proper vapor barrier under the slab, the house is likely doomed before the framing package gets dropped, so double check that the vapor barrier is in place correctly. For crawl spaces, while venting them has been status quo until recently, best practice now is to treat them as conditioned space. LaLiberte's rule of thumb is this: "Any space physically attached to a house must be comfortable enough to take a nap in."

Dry Materials. A simple thing that can help keep buildings safe and customers happy is keeping your stuff dry. "I've seen framing packages slide off the truck with a moisture content as high as 20 percent," says Rudd. "You can build with it, but since mold grows at 16 percent moisture content, you must let the lumber dry out before you close it in." Add to that the umpteen gallons of water in the joint compound (there are 5 gallons of water per 25 pounds of dry mix, says Rudd) and you might as well bring a lake inside.

Install adhesive-backed sill flashing strips. Install corner flashing patches at sill; apply sealant at windo jambs and head or to back of flange.

If your framing arrives dry, cover it. Often drywall hits the site damp -- or even with mold already growing on it. Store it in a dry place and install it dry. This may have a minor impact on a breakneck schedule, but fixing an avoidable problem later -- or getting sued -- takes much more time. The best and quickest way to determine if materials are dry enough to install or close-in is to use a moisture meter.

Tight houses and changes in building materials are only the beginning. Understanding how all the components in your buildings work is also essential to preventing mold -- including HVAC systems, cladding, lawn sprinklers, and grading, depending upon climate.

While redesigning wall sections may sound like starting over, there's a lot of help out there. Thanks to energetic researchers and consultants, there is a nationwide network of experts tracking moisture incursion incidents and recommending solutions. "Builders tend to screw up the same way as each other around the country, pointing to which mistakes are made where," says Environomics' Nassof. He and other experts agree and strongly advise builders to carefully tailor their buildings to their climates. They also say it's essential to understand how all the materials you build with work -- and determine how they work best together as a system. Companies like Environomics, Building Science, and Building Knowledge, and Web outlets like the Energy & Environmental Building Association's www.eeba.org offer climate-specific training for builders. Research is available from the NAHB, too, and at other sites.

Yost points out that all the elements in a house are related and function in unison -- or in contrast -- to one another, and understanding this system is the key to building a house that'll stay dry. "There are very few bad building materials," he says, "but the permutations of bad applications are limitless," pointing to how complicated the detail-decision can be.

"We're asking more from our homes than ever," says Yost. In the recent past, homes were built more to keep water out than to keep heat in. Since then, air conditioning, better heating systems, and the 1970s OPEC crisis required us to build more thermally efficient, yet affordable, products. That's why Yost calls the modern home "high performance." A building does much more than we've ever asked of it in history. And, it often must be built faster with much more-specialized workers. Lightning-fast production schedules and untrained or highly compartmentalized employees lead to mistakes if properly detailing a building penetration requires patience and expertise. All of these forces combined in the last five or so years of record home starts and remodeling activity to create the unintended consequence of mold thriving inside the most advanced houses in history.

Install window; insall jamb flashing first, then head flashing; fold down head housewrap; apply corner patches at head.

As we change what houses do and how we live in them, controlling moisture and creating high-performance buildings you're proud to have your sign in front of is a complex process. It requires changing how we think about building and managing a lot more than water coming at the it from the outside.

Having a mold protocol in place will help you deal with customers' anxieties if they call with a moisture-related question or complaint. Experts Russ Nassof and Bob Rudd recommend the actions below as a preliminary checklist, but also recommend developing a relationship with a professional mold investigator so you can be ready with a quick remedy in case the worst happens.

• Response time is vital. If you don't answer the office phone directly, call back as soon as possible.
• Once the homeowner is on the phone, let them talk as much as possible. Don't interrupt their story. Take detailed notes.
• Document everything -- times, dates, locations, who you're on the phone with, and what they say.
• Get to the site pronto. Stop the water, then determine quickly if you can fix the problem or if it must be handled by a third-party professional.
• When fixing a defect, photograph all stages of the correction process: What it looked like when you got there, what actions you took, and what it looked like when you finished. Digital photography is often best because the camera can time- and date-stamp everything.
• Are there sensitive people on site? (Children under 4-years-old, elderly, immune-compromised.) For a large incursion (i.e. a burst water pipe) that has been there for more than 72 hours, suggest removing them from the site until an investigation can be completed.

Peter Yost at Building Science Corp. outlines the top 12 places his company finds moisture and mold in residential structures. Remedies vary per site.
1. Behind tubs on outside walls
2. Second floor cantilevers
3. Fireplace build-outs/cavities
4. Plumbing/electrical penetrations
5. Rough openings (chimney chases and windows)
6. Attic access -- scuttle holes and fold-down stairs
7. Intersecting inside/outside lines of interior walls and roofs
8. Interior soffits terminating against outside walls
9. Carrying beams extending from inside to outside space (in basements as well as in timber-framed structures)
10. Recessed can lights in thermal envelope
11. Assembly transitions (roof framing to top of second story wall, rim joists, slab to sill plate, etc.)
12. Sheltered spaces, most notably air sealing between attached/under garages and living space

Building Science Corp.: www.buildingscience.com
Building Knowledge Inc.: www.buildingbetterhomes.com
Construction and Environmental Training Institute: www.constructiontraining4u.com
Energy & Environmental Building Association: www.eeba.org
Environomics: www.environomics.com
The Journal of Light Construction: www.jlconline.com
The National Association of Home Builders (NAHB): www.nahb.org
The NAHB Research Center: www.nahbrc.org
National Center for Housing and the Environment: www.housingandenvironment.org
The Insurance Information Institute: www.iii.org
Dr. Fungus: www.doctorfungus.com

<i> -- Mark Clement is executive editor of Tools of the Trade. </i>