Keep Moisture Out of Your Buildings

March 23, 2009

Good moisture-management practices will help stave off mold infestation

Anyone searching for information about mold in buildings will be overwhelmed by the sheer volume of sources. A recent Google check turned up more than 40 million sites that deal with mold.

Given the amount of information available, it's hard to gain a clear understanding of what's important and what's not, or to discern what's accurate and what isn't. As a result, the Responsible Solutions to Mold Coalition (RSMC), based in Chicago, set out to identify simple steps that can be taken during the design, construction, and maintenance phases of a building to keep moisture - and, therefore, mold - at bay.

The RSMC's premise is simple: If you keep moisture out of a building, you'll likely keep mold out as well, since mold requires a moist environment. Other factors come into play, like the presence of mold spores (which are ubiquitous), the addition of a food source, and temperature - but moisture gets priority because it can (and must) be controlled for many reasons. A dry building not only prevents mold outbreaks, but also creates a more pleasant, healthier environment. And, dry buildings are more durable, and will have fewer maintenance problems - so controlling moisture is truly a win-win for builders, owners, and occupants.

Based on keeping moisture out of a building, the RSMC developed Guiding Principles for Mold and Moisture Control. While the principles are based on science, they're clear and easy to follow. No one can guarantee a mold-free building (and it's impossible to condense every relevant factor into such a compact list of principles), but if everyone involved in the design, building, and maintenance of a building remains aware of - and follows - these principles, the vast majority of moisture-intrusion problems will be solved.

Before going through the list of principles, a word should be said about mold-resistant products. There are many excellent products in this category, from mold-resistant gypsum board to mold-resistant paints and finishes. All of them play a role in fighting mold, but they're no substitute for good design, good building practices, and good maintenance. Too often, these products are sold as the silver bullet that will prevent mold - even when proper moisture-management principles are ignored. These products should be viewed as an insurance policy to add robustness to the structure, but not as the first line of defense against mold in the absence of good moisture-management practices. The products are designed to help when the unexpected happens, and moisture enters the building.

The Principles
Building materials must be kept dry. They should be protected from the weather before they're installed; ideally, they should be covered with tarp and raised off the ground. In the case of drywall, it should be delivered to the jobsite close to the time of installation. In addition, there should be sufficient time built into the construction schedule so that wallboard can dry after it rains and before joint compound is applied, or the surface is painted.

SCHEDULE TRADES IN A MANNER THAT PROMOTES MOISTURE CONTROL. A good example of this is the scheduling of the trades that install the roof and cladding. If they're not scheduled properly, you could end up with a leak at the junction of these two planes. Also, keep an eye out for penetrations through walls and ceilings left by plumbers or electricians who must create these holes as they do their jobs. They need to be sealed almost immediately so they don't become a ready source of water intrusion.

ON ROOFS, PROVIDE A CLEAR PATH FOR WATER TO EXIT. Flat roofs need to slope toward a drain. In addition, roof drains need to be kept clear to provide a path for the removal of literally tons of water that can collect on a flat roof. In addition, the roof design needs to accommodate the significant weight of HVAC units and other equipment placed on the roof in order to avoid the creation of water-collecting valleys.

INSTALL PROPER INSULATION WITHIN WALL CAVITIES. Exterior wall cavities should be properly insulated - insulation should completely fill the cavity to prevent the formation of convection cells within the wall that can negatively affect moisture and energy management. Before insulation is installed, it's an excellent idea to vacuum or blow clear all debris that may have collected - when debris combines with moisture, it's an invitation for mold growth. Wet spray-on cavity insulation must be allowed to dry before wallboard installation.

AVOID PLACING PIPES IN EXTERIOR WALLS. There is the obvious concern that pipes in exterior walls, particularly in northern climates, may freeze, but the issue of condensation is equally important. Pipes in exterior walls may generate condensation that can be trapped in insulated walls that can't adequately drain. If pipes must be placed in exterior walls, the insulation should go on the outside of the pipes and wall cavity.

INSTALL WATER-RESISTIVE BARRIERS BEHIND SHOWER INSTALLATIONS. In commercial settings, such as health clubs, water-resistive barriers should be installed behind the shower installation. Water will pass through tile grout; therefore, a water-resistive barrier behind the tile that drains into the shower pan is an important feature, unless specifically recommended to the contrary by the backerboard manufacturer.

SHOWER PANS NEED TO DRAIN. It's important to pay special attention to the grade of any shower-floor installation. If it's not sloped toward the drain, water will pool and could drain toward the wall framing, which, if left continually damp, will induce mold growth.

INSTALL WALLBOARD ONLY AFTER THE BUILDING IS CLOSED IN. Wallboard should only be installed during the controlled phase of construction when the building envelope is enclosed. It's never acceptable to install wallboard before the roof has been installed - and, ideally, it should be installed after the windows and doors are in place. Wallboard should be installed one-quarter-inch off the floor so that minor spills don't come in contact with it. Fill in the resulting space with a sealant to keep the wallboard airtight at its base for energy, comfort, and acoustical control.

VENTILATE DURING CONSTRUCTION. During construction in warmer weather, doors and windows should be kept open to allow for natural drying of joint compound, tile grout, and, eventually, paint. Avoid the use of portable kerosene or propane heaters - they actually introduce moisture into the air. Where warranted, mechanical drying equipment specifically intended to introduce low-humidity air should be considered.

DRY THE CONCRETE FLOORS BEFORE COVERING. Floorcoverings should not be installed over a concrete slab until the floor has dried sufficiently. Uncured concrete introduces gallons of moisture into a new building. It must be allowed to dry through ventilation or mechanical drying.

INTERIOR CONDITIONED SPACES NEED TO BE BALANCED FOR EVEN TEMPERATURE. HVAC systems must be balanced throughout the building to avoid overcooling interior rooms. For example, storage rooms that are used infrequently may become overly cool, which may cause condensation on the walls and ceilings, leading to mold growth.

VENT MOIST SPACES TO THE OUTSIDE. Commercial lavatories and shower facilities require special attention to avoid moisture build-up, which results in mold growth. This includes extra ventilation to the outdoors and the use of an approved tile backerboard around showers. Conventional wallboard is fine to use in the rest of commercial lavatories, but a mold-resistant board will offer greater protection.

COVER MASONRY BLOCK. Because masonry block absorbs water, it should be covered with OSB or other sheathing materials before EIFSs or other siding materials are applied. If there has been a significant amount of recent rain, be sure to allow enough time for the block to dry before being covered with OSB.

DRAIN EXTERIOR WALLS. Exterior walls must be designed to incorporate a water-resistant barrier behind the cladding system, as well as an air barrier and thermal insulation. The barrier must be configured to drain out of the wall, not into the wall assembly. Flashing and overlap details around windows and doors are particularly susceptible to water leakage. Water-resistant and air-barrier designs must be carefully integrated into the wall and joint systems to maintain their functional integrity and durability for the life of the building.

INSTALL ROOF, WINDOW AND DOOR FLASHINGS. Flashings should be installed around all roof lines, windows, and doors, ensuring that the water flows out of the building. Flashings must drain the water onto the water-resistant barrier and to the exterior of the building - not into the building. This requires careful attention to the overlap, gasketing, and sealing details to make sure that gravity and wind-driven rain don't drain into the structure.

PROPERLY FLASH ALL PIPE PENETRATIONS THROUGH THE ROOF. All roof penetrations, such as vent pipes and other HVAC-related piping, should be properly flashed and drained to ensure that water drains to a roof drain or sump, and away from the building - not into the building structure.

GRADE AWAY FROM THE FOUNDATION. The grade around all buildings should slope away from the foundation. The first 10 feet of soil extending outward from the building should be pitched at a 5-percent grade, or 6 inches of fall in the first 10 feet. The slope should be checked every few years to make sure that the backfill has not settled.

INSTALL PERIMITER DRAINS. By ringing the foundation both inside and out with perimeter drains, water will be taken away from the base of the foundation, thereby keeping the foundation and basement dry. It's important that these drains be installed so they eventually reach daylight or enter a sanitary sewer, if code allows.

DIRECT NEAR-FOUNDATION IRRIGATION AWAY FROM THE BUILDING. Irrigation poses three water-intrusion risks: 1) daily presence of water near the foundation increases the chance that water will enter the building through cracks in the foundation, 2) a broken spray head can place massive amounts of unwanted water near the foundation, and 3) an incorrect spray head or a misdirected water arc may result in water being sprayed upward against the walls and windows.

COAT VERTICAL FOUNDATION WALLS ON THE OUTSIDE WITH A VAPOR BARRIER. Cement is porous and, without the protection of this type of barrier, water moving down the side of the foundation may be absorbed and make its way into the basement.

There are myriad steps that building owners can take to keep their buildings dry once they're completed. The details for these steps are included on the RSMC website (www.responsiblemoldsolutions.org). Building owners and managers need to be on the lookout for standing water or slow water leaks caused by blocked drains, broken pipes, or excessive humidity (among other things). The RSMC highly recommends that, four times per year, someone performs an inspection of all spaces within the building, looking for the presence of water. Once the water is identified, it's important to try to find out where the water is coming from, and where it goes. Steps should be taken to curtail the water intrusion; once the site is dry, building materials should be evaluated for replacement.

Keeping buildings dry, healthy, and safe isn't a complicated process. It requires attention to detail and constant vigilance so that small problems don't become large ones. Download Guiding Principles for Mold and Moisture Control, and keep the document handy on the jobsite as a checklist to make sure these simple steps are taken to protect your buildings.

Christopher D. Pinckney is a member of the Chicago-based Responsible Solutions to Mold Coalition's Technical Committee.

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